Vitamin D and calcium go hand-in-hand for promoting good bone health. While most people are attuned to calcium, vitamin D is another story. You probably know what your cholesterol is, or at least you have had it checked. But do you know what your vitamin D level is?
The majority of Americans have not had their vitamin D level checked. If you are among those who have not, you may have compelling reasons by the end of this chapter to have vitamin D included with your next blood tests. On the other hand, if you have had a recent vitamin D level, have your number handy while reading the chapter.
The evidence for bone health, based on calcium absorption and its skeletal effects, sets 30 ng/ml as the minimum level of vitamin D. I start my lectures on vitamin D with the number 30. Remember: 30 is key to your bone health. That guidance may change in the future, as new research emerges about the influence of vitamin D in other areas beyond bone and muscle health. For now, 30 is the number to keep in mind, and there is a very good chance your vitamin D is below this minimum level.
VITAMIN D BLOOD LEVELS
The barometer for your vitamin D status is a measurement of your blood level of “25-hydroxyvitamin D3” (also written as “25(OH)D,” which is descriptive of its structure). For vitamin D levels, this is what is actually measured in the laboratory, and it is what you may see written on your laboratory results. The “ng/ml” is just the unit of measurement most common in the US. In your reading, you may also come across another unit of measurement: nmol/L. To convert to ng/ml, divide this number by 2.5. (Example: 80 nmol/L 2.5 = 32 ng/ml)
Just as the cutoff for high cholesterol has changed, the definition of low vitamin D has been a moving target as well. There is controversy and plenty of debate over what is the correct minimum level of vitamin D. In the scientific community, the debate revolves around the minimum level of 20 versus 30 ng/ml. The Institute of Medicine committee that updated the vitamin D dietary reference intakes in 2010 chose the level of 20 ng/ml.
However, other experts who have examined the same evidence conclude that 30 ng/ml is the minimum level based on calcium absorption, bone health, and muscle function. I share this opinion. In addition, what is established as public health policy may not apply to a particular individual's situation.
If identifying the minimum level of vitamin D seems difficult, pinpointing the optimal level is an even trickier subject. Vitamin D is used by practically every tissue in the body, and it is difficult to know what might work best for one area and what may not be enough for another. The Institute of Medicine committee suggests an upper level of 50 ng/ml. Using “reasonable extrapolations” from the data for maximum reduction of multiple diseases, other experts recommend an optimal vitamin D range of 40 to 60 ng/ml. Considering that the typical American's vitamin D level is quite a bit less than 30 ng/ml, this range is a lofty goal.
Laboratories typically give values between 30 and 70 ng/ml as the normal value range. Don't be alarmed if your laboratory lists different numbers. This variability just demonstrates the problem: lack of standardization of categories. These levels will continue to be a source of debate in the medical community, since more research is needed to fill in the knowledge gaps.
ARE YOU AT RISK FOR LOW VITAMIN D?
Yes, you are, and so is everyone else. Vitamin D deficiency is at epidemic proportions, despite the common use of vitamin D supplements. National data from the National Health and Nutrition Examination Survey (NHANES) show a marked decrease in vitamin D levels since the 1980s. Numerous factors play a role, such as your exposure to sunshine, body size, skin color, where you live, and your age.
In our modern era of healthcare, vitamin D deficiency was previously thought to be primarily a problem for older adults, particularly those confined to home or living in nursing homes. Recently, study after study has shown that low vitamin D is a worldwide problem, regardless of one's location, age, sex, or ethnicity. It is pervasive in the US, even in places with plenty of sunshine. Even among women taking prescription medicines for osteoporosis, who would be expected to have increased awareness of the importance of calcium and vitamin D, more than half in a study of more than 1,500 women from across North America had low vitamin D levels. It is not just a problem in women, but affects men, women, and children alike.
Clearly, what the average American is doing is not enough. Dr. Michael Holick, a leading vitamin D researcher based at Boston University School of Medicine, said, “It is inconceivable with all the advances in modern medicine that vitamin D deficiency should be a health concern in the United States.”
ABC…WHERE IS D?
Sunshine
The majority of vitamin D results from your skin being exposed to the sun. Actually, this exposure is the first step that sets in motion the chain of events that produce vitamin D. All you need is ten to fifteen minutes of sunlight two or three days a week. If you have a darker skin color, it will take longer. On average, it takes only fifteen minutes a day in the midday hours to get enough sunlight. Dr. Robert Heaney, a distinguished professor at Creighton University School of Medicine, estimates that the average person gets 2,000 IU of vitamin D from the sun each day (IU is a standardized unit of measurement short for International Units; one IU of vitamin D is equivalent to 0.025 micrograms). But—there is always the fine print—multiple factors determine whether sunlight will actually provide you with enough vitamin D.
You need to be outside in the middle of the day, and you need to have enough skin exposed—at least your face, arms, and hands. At noontime, two or three days a week, I used to shed my white coat and go up on the rooftop of our research building with my brown bag lunch to get my quick fifteen minutes of “vitamin D therapy.” Beyond your vitamin D therapy time, you will need to prevent sunburn and potentially long-term skin damage from excessive sun exposure.
YOUR STORIES…
Sarah, age fifty-five, anesthesiologist in North Carolina:
“I leave and come home in the dark. I was not taking any supplements. Even one of the orthopedic surgeons told me he had low vitamin D, too.”
Sarah does not see the “light of day.” She leaves for work in the dark, works in operating rooms devoid of any natural light, and returns home long after peak sun-exposure time. Her vitamin D level was quite low, 16 ng/ml, when it was first checked after Sarah experienced rapid bone loss.
Like Sarah, you may rarely be outside during peak ultraviolet light to have a chance to make vitamin D. Natural light inside the building would not have helped her either. Glass filters out too much of the ultraviolet light that is needed for production of vitamin D. You might feel better having a window, but you need to be outside to get the benefit of nature's vitamin D therapy.
A note of caution: Dermatologists warn anyone who has a skin type that burns easily or has a history of skin cancer that they should not have casual, unprotected sun exposure. If you are in that situation, use sun precautions and make sure you are getting vitamin D from other sources.
Peak ultraviolet light is needed to have a chance to make vitamin D. But wait! You might not need to rush outside just now.
What Time of Year Is It?
Time of year makes a difference since sunlight varies seasonally.
In Boston, Dr. Holick placed a photometer on the roof of Boston University Hospital to monitor the level of ultraviolet radiation. He measured adequate sunlight for making vitamin D during only four months of the year, from May to September. Dr. Holick also drew blood samples once a month from volunteers. Their vitamin D levels showed a seasonal pattern. The levels were highest at the end of the summer, then drifted down and were lowest at the end of winter.
Summer may be the only time you can count on sunshine as your source of vitamin D, and the effectiveness also depends on how much sunlight is available. Different weather patterns or atmospheric conditions may even sabotage that time of year.
Where Do You Live?
Location, location, location.
Okay, so sunshine is not a dependable source of vitamin D in Boston except during the four summer months out of the year. What about other parts of the country? Since San Diego has more apparent sun, you would not expect any problems with getting vitamin D there.
In 1993, Dr. Clifford Rosen, an endocrinologist and research scientist at Maine Medical Center, and I compared older women from San Diego with women from Maine over a period of one year, from one summer to the next. Dr. Rosen was based in Bangor, Maine, and expected to see vitamin D levels highest at the end of summer and lowest in the winter. We did not expect to see the same pattern in the San Diegans. Contrary to our predictions, the seasonal changes in vitamin D levels were identical for both groups.
As you can see, the graph plotting the change in vitamin D levels for each group looked like superimposed Vs. The graph started at the first summer, the bottom of the “V” was the winter, and the second summer reverted to the same levels as the first summer. What struck me on rereading this paper is that none of the Maine or San Diego women had vitamin D levels above 30! The average summertime highs for both groups were 25 ng/ml. At the time this study was performed, the lower end of the normal reference range was 10 ng/ml. We have come a long way in our understanding of vitamin D and bone health since the early 1990s.
One more important point was made from this comparison. The seasonal changes in vitamin D and corresponding changes in higher parathyroid hormone translated into seasonal bone loss. This study demonstrated for the first time that wintertime bone loss was not exclusive to people living in northern latitudes. In addition, it might explain the observation that hip fractures are more common during winter months, even in places with no snow or ice. So I may be able to gloat about the sunny seventy-degree day in January, but San Diegans do not appear to be getting enough wintertime vitamin D, either.
Let us look at another state with sun: Florida. In the “Sunshine State,” you'd think you would be more likely to have adequate sunlight throughout the year.
After a few reports had shown remarkably high occurrence of inadequate vitamin D levels in different parts of the country and the world, University of Miami endocrinologist Dr. Silvina Levis decided to perform a study of her patients in the Miami area. Dr. Levis and her associates recruited about two hundred men and women from the general medicine outpatient clinic. Vitamin D levels were checked at the end of winter and rechecked at the end of summer. The majority of vitamin D levels were lower than 30 ng/mg regardless of season.
Dr. Levis explained, “We thought that because of our southern, sunny location this would not be the case in Miami. Our results proved us wrong. We stay away from the sun, we use sunscreen, and we walk on the shady side of the street. Therefore, we have rates of low vitamin D that are pretty close to what has been found in locations farther away from the equator.”
Low vitamin D occurs even in places with abundant sunshine.
Do You Use Sunscreen?
Dr. Levis mentioned sunscreen as a contributing factor for seeing more people with low vitamin D. You have probably been admonished by your dermatologist to wear sunscreen, wear a hat, and cover up. Sunscreens block the production of vitamin D because sunscreen does its job by blocking ultraviolet light. So, if you use sunscreen you have little chance of activating the vitamin D precursor that starts the cascade of events that results in the production of active vitamin D. Unfortunately, there is no sunscreen that lets in some of the “good stuff.”
In some studies, sunscreen users tend to have higher vitamin D levels. It may be that sunscreen users end up with more overall exposure to the sun. Other studies, like the Maine versus San Diego study, showed opposite results. When we looked at sunscreen use among San Diego women, there were no differences in vitamin D levels during the summer. In winter, sunscreen users showed greater declines in vitamin D levels and increases in parathyroid hormone compared with the group that did not use sunscreen.
Dermatologists have been effective in delivering their message to use sunscreen and protective clothing. Sunscreen is just another reason you cannot count on sun for maintaining healthy vitamin D levels.
What Do You Wear?
The specialty sun protection clothing market has made its way into mainstream clothiers and stores. You may notice clothing with UPF ratings. Ultraviolet Protection Factor (UPF) is like the sun protective factor (SPF) used on sunscreen lotion bottles. However, clothing does not need to be specially made to block ultraviolet rays. Even normal daily clothing effectively blocks the ultraviolet radiation needed for producing vitamin D. Because clothing and sunscreen work so effectively, you will need to have another source of vitamin D.
What Is Your Skin Color?
The darker your skin, the longer you need to expose yourself to sunlight to produce adequate levels of vitamin D. Increased skin pigment (melanin) reduces the capacity of the skin to make vitamin D. The melanin in the skin acts as a natural sunscreen.
Lower vitamin D levels are observed in African Americans compared with Caucasians; Mexican Americans are in between. These studies have included children, adolescents, and younger and older adult men and women. Lower vitamin D levels are common in anyone with darker skin pigmentation.
However, African Americans have a much lower risk of osteoporosis and fractures. Reasons for this paradox are not entirely clear. It appears that the body adapts to low levels of vitamin D and bone loss does not seem to occur. It is thought that the kidney may compensate by not allowing as much calcium to end up in the urine.
Researchers are trying to explain this genetically programmed advantage. Because of the adaptations by bone and kidney, vitamin D may not be as important for maintenance of African Americans' bone health. However, the benefits of maintaining adequate vitamin D may have a role in other diseases.
Darker skin, regardless of your ethnic or racial background, predisposes you to vitamin D deficiency. If you have darker skin, longer sun exposure is needed to achieve adequate vitamin D levels. So, compared to fair-skinned individuals, you will need to pay attention to getting an even higher amount of daily vitamin D combined from all sources.
Low Vitamin D Levels in Girls
In a nationally representative sample of girls and young women, the likelihood of low vitamin D increased with age. The striking finding was that the majority of all girls, except young Caucasian girls, had low vitamin D. Nearly 100 percent of the African American teens and young women had inadequate levels. All children, and particularly those with darker skin color, urgently need to be targeted for supplementation.
Is It in Your Genes?
Beyond skin color, is there something else you inherited that may contribute to your vitamin D levels? Recent genetic research suggests that vitamin D genes may make a difference in how you respond to sunshine.
What Is Your Body Size?
One size does not fit all. The larger you are, the more vitamin D you need. Even though large or overweight people may not be at as a high a risk for fracture as thinner individuals they are at high risk for low vitamin D. Think about it as having to fill up a small car versus a large car at the gas station. The larger car is going to require more gallons than the small car. A larger person requires more vitamin D to get a “full tank.”
What Is Your Age?
For years, it was thought that older people were the only group who required more vitamin D than everyone else because of their inability to get enough vitamin D through casual sunlight. As you age, your skin tends to get thinner, with a decrease in both the top skin layer (epidermis) and the fat layer of skin (dermis). This results in less precursor vitamin D available to start the cascade of vitamin D production. Even with adequate sunlight, older skin cannot produce enough vitamin D. Therefore, you need to compensate by getting more vitamin D from sources other than the sun. If you are older, the second strike against your ability to make active vitamin D is a decrease in the efficiency of your kidneys, which results in lower production of the active form of vitamin D.
What Is the Bottom Line about Sun as a Source of Your Vitamin D?
As you have just read, many factors modify the intensity of sunlight, including season of the year, weather, atmospheric conditions, and geographic location. The ability of ultraviolet rays to penetrate the top layer of skin to start the production of vitamin D is modified by skin pigmentation, aging, clothing, and the use of sunscreen. Therefore, it is quite difficult to count on sunlight to keep your vitamin D at a healthy level. So count out the sun as a source, at least for eight months of the year. During the summer months you might have a fighting chance, but you are probably inside during the midday when the sunlight is best for making vitamin D. Even if you are outside, use of sunscreen and many other factors are working against you. There are just too many barriers that prevent you from counting on casual sunlight as your main source of vitamin D.
What are you to do now? Where else are you getting vitamin D? Let us look at food sources.
FOOD
You may be thinking, “I am getting it in my food. I eat a healthy, balanced diet most of the time, so food must be my source of vitamin D.” Well, probably not.
What food can you eat for vitamin D?
Interestingly, few foods naturally contain vitamin D. The main food sources of vitamin D are oily fish, such as salmon, mackerel, and sardines, and eel. Other foods, such as egg yolks and liver, contain only small amounts of vitamin D. While the Eskimos' diet of fatty fish compensated for their lack of sunlight exposure, the diets of most Americans are not adequate to supply the majority of our vitamin D needs.
Although salmon is one of the most consumed fish in the US, unfortunately, eating salmon does not guarantee that you are actually getting vitamin D. You need to pay attention to whether the salmon is farm-raised or wild. The nutrient-poor diets of farm-raised salmon translate into little available vitamin D. Also, compared with salmon caught in the wild, farm-raised salmon contain much lower quantities of the good omega-3 fatty acids.
You may have been given cod liver oil as a child or have seen pictures of kids being given a teaspoon filled with it. One teaspoon of cod liver oil contained about 400 IU of vitamin D, which was enough to prevent rickets. It was advertised as “Bottled Sunlight,” rich in sunshine vitamin D. It is not used now because of its high content of vitamin A, which is detrimental to bone health—not to mention its intense, fishy smell and taste.
In the past, many more foods were fortified with vitamin D. For example, the Joseph Schlitz Brewing Company, producers of Schlitz, known as “The Beer That Made Milwaukee Famous,” fortified their beer with vitamin D for three years from 1935 to 1938. A magazine ad page from 1936 proclaimed: “Keep Sunny Summer Health—Drink Schlitz All Winter.”
Today, few foods are fortified with vitamin D. The most common fortified product is milk. An eight-ounce glass (one cup) of milk contains 100 IU of vitamin D3. On your milk bottle or carton, the Percent Daily Value (DV) is listed for a one-cup serving as 25 percent vitamin D—meaning 25 percent of 400 IU RDA. A shortened calculation is to multiply % DV times 4 (for milk example, 25 × 4 = 100).
Other fortified foods include cereals, some brands of orange juice, and other dairy products. Generally, cheese and ice cream are not fortified but yogurt may be. You must check the labels. Take a look at the foods listed on the following table. There are not many available sources rich in vitamin D.
| Vitamin D Food Sources | ||
| Food | Serving Size | Approximate Content (IU) |
| Fish | ||
| Halibut | 3 ounces | 200–300 |
| Herring | 3 ounces | 96 |
| Perch | 3 ounces | 49 |
| Salmon, wild, filet | 3 ounces | 350–800 |
| Sardines with bones | 3 ounces | 160 |
| Trout | 3 ounces | 600 |
| Tuna, canned | 3 ounces | 154 |
| Other Natural Sources | ||
| Egg | 1 large | 41 |
| Liver, beef | 3 ounces | 42 |
| Vitamin D-Fortified Foods (check labels) | ||
| Bread | 1 slice | variable |
| Cereals | ¾ to 1 cup | variable plus add milk |
| Margarine | 1 tablespoon | variable |
| Milk, all types | 1 cup | 100 |
| Orange juice | 1 cup | 100 |
| Yogurt, plain nonfat | 1 cup | variable |
So in reality, fortified foods are not an efficient way of raising or maintaining your vitamin D level. It is difficult to get enough vitamin D from your diet alone, even if you eat four to five servings of oily fish each week. The assumption has been that foods fortified with vitamin D will help you meet your daily requirements, but clearly, that is not the case. Data from a nationally representative sample (NHANES), collected in 2005 to 2006, showed that less than 10 percent of all adults age fifty-one to seventy were getting 400 IU of vitamin D from diet alone and less than one percent of those age seventy-one and older had diets containing 600 IU.
Sun is a negligible source, except during the summer. Food is not adding much, unless you drink a lot of milk or eat wild salmon for most of your meals. What is left to do? It boils down to supplements.
Dietary Reference Values for Vitamin D 2010
| Daily Recommended Dietary Allowance Vitamin D Intake | ||
| Age in Years | Amount in International Units (IU/day) | Upper Level Intake IU/day) |
| Infants 0 to 6 months | 400 | 1000 |
| Infants 6 to 12 months | 400 | 1500 |
| Children ages 1 to 3 | 600 | 2500 |
| Children ages 4 to 8 | 600 | 3000 |
| Children ages 9 to 18 | 600 | 4000 |
| Adults ages 19 to 50 | 600 | 4000 |
| Adults ages 51 to 70 | 600 | 4000 |
| Adults ages 71 and older | 800 | 4000 |
Updated Dietary Reference Intakes (DRIs) for vitamin D were released by a committee of the Institute of Medicine in 2010. Despite the plethora of new evidence that has emerged since values were first set in 1997, the evidence supports vitamin D for bone health but not for other diseases or conditions. Even for bone health, there are few studies using supplementation above 800 IU per day. Note that these recommended values support a blood level of 20 ng/ml.
There are still many unanswered questions. Clinical trials using higher supplementation are currently being conducted, but it will be years before definitive results from these studies will be available.
The recommended dietary allowances are public health recommendations that serve as general guidance, and they are safe and reasonable. For individual care, assess your needs in the context of your personal health with your doctor.
SOURCE: Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
Supplements
How Much Vitamin D Do You Need?
The recommended values work as a whole for a public health message, but they may not necessarily meet an individual's specific needs. You can take 600 to 800 IU a day and still be under the minimum vitamin D level of 30 ng/ml.
The best approach is to know your starting vitamin D levels to determine the amount you will need to supplement. However, testing everyone is neither practical nor cost effective. A practical way to start is with 2,000 IU each day of supplemental vitamin D for adults. After three to four months of use, if you are at high risk for osteoporosis, have had fractures, have malabsorption, are overweight, or have other chronic diseases, then you may want to have your blood level checked. A good time for this is during the winter or early spring when your levels may be lowest.
Children
The American Academy of Pediatrics' latest recommendation, from 2008, is to give all breast-fed infants 400 IU of supplemental vitamin D. Infant formulas contain vitamin D in the amount of 400 IU per liter. This amount was incorporated in the latest update (2010) from the Institute of Medicine.
The recommendation for children is to increase vitamin D supplementation to 600 IU a day. The same amount is also recommended for preteens and teens. However, some research shows that vitamin D requirements increase with growth and larger body size. Therefore, vitamin D should be adjusted for body weight. Dr. Robert Heaney, distinguished professor at Creighton University School of Medicine, estimates that 75 IU of vitamin D per kilogram is needed from all sources combined to ensure adequate vitamin D. The problem is that there is no way to estimate the amount of vitamin D from sunlight exposure. As children and teenagers approach adult size, higher doses may be needed. Talk with your pediatrician about how to individualize your child's vitamin D intake.
Vitamin D is a basic requirement for the growing skeleton. Outside of bone health, it is not clear what long-term role vitamin D may play in the prevention of other diseases and in establishing lifelong health. Vitamin D is essential for the health of our children.
What kind of vitamin D are you taking?
Take a look at your multivitamin and calcium supplement bottles. Chances are you will need a magnifying glass or bifocals to read the small print. Turn your attention to the “Supplement Facts” on the bottle. The vitamin D could be identified as vitamin D, vitamin D2, vitamin D3, or by the less-obvious names “ergocalciferol” or “cholecalciferol.” It may take some sleuthing. Vitamin D could be listed as “vitamin D” in the amount-per-serving table, but you will need to look in the ingredients list to determine if it is identified by type there. It could be identified as “ergocalciferol” or “cholecalciferol” in the ingredients list.
Ergocalciferol is vitamin D2, which comes from plant sources. It is made by ultraviolet irradiation of ergosterol, which is a compound from yeast. Cholecalciferol is vitamin D3, which is the vitamin D that our bodies naturally produce. It is produced from ultraviolet irradiation of the precursor of vitamin D (7-dehydrocholesterol) in the skin. For supplements, it is obtained from the lanolin of sheep's wool.
Conventional teaching says that D2 is not absorbed as well as D3. So it takes approximately one-third more vitamin D2 to create the same increases in vitamin D levels that you would get from vitamin D3. The major vitamin manufacturers took heed and many have reformulated their products to include vitamin D3 rather than vitamin D2. All vegetarian-only vitamins contain vitamin D2. Those labeled “natural” tend to contain vitamin D2, but not always. Interestingly, the only prescription vitamin D in the US is vitamin D2. But there has been a movement to get it changed to vitamin D3.
A few recent publications have shown that a 1,000 IU dose of vitamin D2 daily is as effective as a 1,000 IU dose of vitamin D3 in maintaining vitamin D levels. So whether you take a daily product with vitamin D2 or D3 may not matter. However, since the preponderance of research definitely favors vitamin D3, I suggest that once you use up your current vitamin bottle you should change brands to one that uses cholecalciferol—vitamin D3—because of its superior potency. In any case, it is your overall vitamin D level that is important, not the amount you are taking.
You do not need to take vitamin D every day. If it is more convenient to think about it once a week, then take your dose that way. You just need to make sure that the supplement you are taking is effective for maintaining a good vitamin D level. If you are starting out with a low vitamin D level, you need to have a follow-up in about four to six months to be sure that the extra vitamin D you are taking is sufficient to increase your level above the minimum level of 30 ng/ml.
Multivitamin supplements also contain vitamin D. The amounts of vitamin D range from 100 IU to 1,800 IU per tablet. There are differences not only between brands but also between categories: children's, prenatal, men's, women's, and over fifty. You need to pay close attention and read the labels carefully with each and every new purchase of supplements. Also, look closely at the serving size. You will need to figure out how many pills, chews, or liquid measures equate to the amount listed for vitamin D.
What is on your shelf? How much vitamin D are you taking?
You will need to take an inventory to figure out how much vitamin D you are getting. If you are taking vitamins and supplements, take the time to gather all your bottles and review the labels. Most likely your multivitamins and calcium are the only products that have some vitamin D. Multivitamins typically have 400 IU, but it could be more or less. Also, pay attention to the Serving Size. Is it one, two, three, or four tablets for which the content information is given?
Remember to check each time you buy a new bottle of supplements; you will need to recheck the supplement facts.
Do you get extra vitamin D from diet or sun?
It is difficult to gauge your sun exposure. Beyond casual exposure, most people cannot count on a significant amount. Dietary enrichment of foods also accounts for only small amounts of vitamin D. You would basically need to eat fish three times a day to have enough from your diet, and few people follow an “Eskimo diet.” Some brands of products such as yogurt or soy milk may have vitamin D added, but even then it is a small amount. To ensure a consistent source of vitamin D, you will need to supplement. For the “average adult,” 2,000 IU each day should maintain a vitamin D level over 30 ng/ml.
What if your blood level is below 30?
Discuss with your doctor how to supplement vitamin D in order to raise your level to above 30 ng/ml. There are many different safe and inexpensive ways to achieve a higher level; if you ask ten doctors, you might get ten or more different approaches. Some of these approaches have been evaluated in research studies; others have not. The goal is first to attain optimal vitamin D levels, and, second, to prevent the level from dropping below 30 again.
Here are several common recommendations:
Vitamin D2 50,000 IU weekly (available by doctor's prescription only)
Vitamin D3, 50,000 IU weekly (available online or by special order at your pharmacy)
Take one capsule once a week for eight weeks. That is equivalent to a base dose of about 7,000 IU per day. Recheck your blood level after eight weeks. If your blood level is still less than 30 ng/ml, take 50,000 IU of vitamin D2 once a week for another eight weeks, then recheck blood levels.
When you reach the target blood level of 30 ng/ml, you have several options. You can keep using 50,000 IU of vitamin D2, but take one every other week. Or you can switch to a lower daily dose of 2,000 IU. Note: Your daily dose will need to be individualized based on your requirements to maintain a level in the optimal range.
For D2, the longest interval between taking two doses should be two weeks. Prescriptions sometimes call for taking D2 once a month but the dose does not last that long. However, a once-monthly dose of D3 does last the full month and can be given at that interval.
Daily Dosing
A general estimate is made to determine your additional daily vitamin D supplementation. After taking the daily dose for three to four months, recheck your vitamin D level.
Estimating Additional Vitamin D
Dr. Robert Heaney and his group at Creighton University studied responses to different doses of vitamin D to develop a prediction rule of thumb. Their subjects were 116 healthy men who were given vitamin D3—cholecalciferol—for eight weeks during the winter. Note that these were healthy men, average age twenty-eight, who started the study with an average vitamin D level of 26.8 ng/ml.
Based on the observed vitamin D level responses to vitamin D supplementation, Dr. Heaney predicted that a daily dose of 400 IU would increase levels by 4 ng/ml. The 1,000 IU dose should increase levels by almost 10 ng/ml.
The “rule of thumb” is based on these observations, but it does not account for individual variation. For example, if you are overweight, you may need even more vitamin D. Since vitamin D is stored in fat, it will take more to fill up the storage area.
If you use the general rule of thumb that each additional 100 IU raises your blood levels 1 ng/ml, you can make a general estimate of what your additional daily needs are if your level is low. For example, if we go back to Sarah (see page 144), who had a starting vitamin D level of 16, she will need 14 × 100 = 1,400 extra units/day on average to raise her level to the minimum 30 ng/ml.
Can you take or get too much vitamin D?
Theoretically, yes. In all practicality, probably not. Only a few cases of toxicity have been reported. In medical school, we were taught to be careful with the vitamins A, D, E, and K because they are stored in fat or are so-called fat-soluble vitamins. This teaching has contributed to a reluctance to give “too much” vitamin D. Several previous studies have also questioned whether vitamin D causes kidney stones. However, doses of vitamin D that result in blood levels in the normal range do not cause kidney stones.
Actually, a large margin of safety exists between the normal levels of 30 to 70 ng/ml and toxicity, which occurs at levels of 200 ng/ml and higher. Toxic levels of vitamin D cause excessive calcium in the urine and blood. Symptoms of toxicity are related to the high blood calcium levels and may start with loss of appetite, nausea, and vomiting.
Think of jobs with sun exposure—outside workers, lifeguards, and the like. Typically, lifeguards have blood levels of 60 to 80 ng/ml. The skin has a built-in safeguard so that you can't reach toxic levels of vitamin D from overexposure to the sun. Though repeated and prolonged sun exposure will not result in toxic levels of vitamin D, your dermatologist will not be too happy with you.
However, unlike exposure to sunlight, you can reach toxic vitamin D levels from taking large quantities of supplements. A safe estimate for an upper intake level is daily doses of 10,000 IU a day, although the Institute of Medicine sets 4,000 IU a day as the adult upper level. Fortunately, you will not need to go that high to maintain optimal vitamin D levels. It turns out that there is a wide safety margin. But don't go overboard with your supplements. You can get too much of a good thing.
A study published in a 2010 issue of the Journal of the American Medical Association showed increased falls and fractures with vitamin D supplementation. This finding was the opposite of what was expected. Subjects in this randomized clinical trial (more than 2,200 Australian women age seventy or older) used either a dose of 500,000 IU of vitamin D3 or a dummy placebo once a year. Study subjects were followed for three to five years.
Dr. Reinhold Vieth, vitamin D expert at the University of Toronto, explained that “the problems arose because of the long dosing interval, and not because of the cumulative dose, or the serum levels attained.” In other words, it was not a toxicity problem. The effect of vitamin D3 lasts two to three months. The interval of one year did not make biologic sense.
A word about laboratory testing
At the present time, two different methods (also called assays) are used to measure vitamin D levels in the blood. Both types should provide reliable and accurate results. There is no standardization of vitamin D laboratory testing. However, all laboratories have internal quality control measures in place. Just as with any other test, if your result is exceedingly high or low, you should have it redone.
WHY IS VITAMIN D IMPORTANT?
After all this information about vitamin D, why is it really necessary?
Calcium Balance
The main function of vitamin D is to preserve calcium balance. How well calcium is absorbed from the intestine is regulated by vitamin D. With adequate vitamin D, you absorb about 30 to 40 percent of the calcium that you take in from foods, drinks, or supplements. If your vitamin D level is low, the efficiency of calcium absorption drops to 10 to 15 percent. This comes at great cost to your bone health. Too little vitamin D results in a cascade of events that lead to increased fracture risk.
When not enough calcium is coming in, the body has a mechanism to get more calcium in order to keep everything running. The parathyroid's sole role is to regulate calcium in your body. Your parathyroid consists of four small glands that are located in your neck, usually on the backside of your thyroid, hence the name. Low calcium in the blood triggers the parathyroid gland to go into overdrive to produce more of its hormone, “parathyroid hormone.” You may see it abbreviated as “PTH.”
The increased amount of parathyroid hormone acts on the bone to release some of its calcium. This makes up for too little calcium being absorbed in the intestine, but it is at the cost of the bone. Bone is broken down faster than normal, and this causes a net bone loss. The accumulated effect of bone loss is weakening of bone structure and a much higher risk of fractures.
The goal is to have enough vitamin D to prevent the cascade of events that leads to bone loss, osteoporosis, and fractures. The level of vitamin D needed for calcium absorption defines the vitamin D level needed for bone health. The critical threshold level for vitamin D is 30 ng/ml, which allows you to absorb adequate calcium and prevent the overproduction of parathyroid hormone.
Parathyroid hormone levels move in the opposite direction from vitamin D. You can think of a teeter-totter, as one end goes up the other goes down. I also need to note that it is possible to have a low vitamin D level with a normal PTH. The lower your level, the more likely it is that your PTH is high. However, the expected response in PTH may be blunted by other factors, such as smoking or being overweight.
For example, when Sarah had a vitamin D level of 16 ng/ml, her parathyroid hormone (PTH) level, at 65 pg/ml, was high (normal PTH values are 10 to 55 picograms per milliliter (pg/ml) but may vary between laboratories). She started taking vitamin D supplements. On a subsequent recheck, her vitamin D level had improved to a normal level, 47 ng/ml, and her PTH had decreased to 35 pg/ml, which was in the normal range as well. By simply increasing your intake of vitamin D, you can steadily regain proper balance.
Bone Density
Higher vitamin D levels are associated with higher bone density. When vitamin D versus bone density is plotted out, there is a steep curve up in bone density to a vitamin D level of 36 to 40 ng/ml. Above those levels, the bone density levels out to a plateau. Therefore, it is advantageous for your vitamin D level to be in the 30s for optimal bone density.
Fractures
It follows that if your bone density is lower then your fracture risk is higher. Clinical trials using vitamin D alone or in combination with calcium have been done to evaluate the risk of fracture. These were randomized, placebo-controlled studies, which means that by chance some subjects received the active ingredient, in this case vitamin D, or sometimes vitamin D with calcium. Others got an identical imitation pill called a “placebo” that did not contain vitamin D.
The data from individual studies were combined and redone in a new analysis, called a “meta-analysis.” Multiple meta-analyses have been done to evaluate the effective dose for fracture reduction. The investigators found that only daily vitamin D doses of 700 to 800 IU were effective in decreasing the risk of fractures. There was an approximately one-quarter reduction of risk for hip fractures and any nonvertebral fracture. No benefit was observed in trials that used lower daily doses.
Rickets and Osteomalacia
The classic vitamin D deficiency disease in children is rickets, which results in malformed bones. When the same process happens in adults, the condition is called osteomalacia. Osteomalacia means soft bones. That is literally what happens. Very low vitamin D levels result in an inadequate supply of calcium and phosphorus, which are necessary to make the bones solid through a process called mineralization. If new bone does not mineralize, it is soft and rubbery.
In children, depending on their age, a variety of deformities of the bone may occur. These deformities are accentuated by the effects of gravity. A classic picture of rickets shows a child of diminutive height with bowed legs and a prominent head. Unfortunately, this disease still happens, not just in developing countries but in the US as well.
In adults, no outward signs of osteomalacia are usually seen. Instead, bone and muscle pain, as well as tenderness, are common. Because the pain can be dull and constant, it may be misdiagnosed as fibromyalgia, a disorder characterized by widespread musculoskeletal pain with localized tenderness and fatigue. Anyone with persistent and nonspecific musculoskeletal pain who has not responded to usual care should have his or her vitamin D level measured. The risk of fracture with osteomalacia is high. If a fracture does occur, osteoporosis may commonly be diagnosed instead of the real problem: osteomalacia as a result of vitamin D deficiency.
In addition to low levels of vitamin D that are typically less than 15 ng/ml, osteomalacia is often accompanied by other abnormal test results: low blood calcium and phosphorus and increased parathyroid hormone and alkaline phosphatase. Alkaline phosphatase is an enzyme that reflects both liver and bone activity. In this case, alkaline phosphatase levels are often high because the bone-building cells, osteoblasts, are working overtime. Early in the disease process there may be enough compensation so that some of the blood studies may still show results in the normal or close to normal range.
Don't Confuse Osteomalacia with Osteoporosis
Academy Award-winning actress Gwyneth Paltrow posted a story in her website newsletter GOOP entitled “Vitamin D.”
The British press picked up her story and went to town with the information as only the Fleet Street reporters can do, penning headlines like “Diet Fan Gwyneth Paltrow Has Bone Disease” and “Gwyneth Paltrow: I'm Suffering from Brittle Bone Disease.” In her online newsletter, she revealed that she'd had a “tibial plateau fracture a few years ago.” (The tibia is your shinbone. Fracture of the tibial plateau occurs in the wide part of the tibia just below your knee). Because of the fracture, she'd had a bone density scan that showed she had the “beginning stages of osteopenia.” That result led her doctors to test her vitamin D. She was told that it was the “lowest they had ever seen.”
Based on her post, the Fleet Street reporters diagnosed her with osteoporosis.
They jumped to the wrong conclusion.
She most likely had “osteomalacia.”
Her fracture of the tibial plateau is not a classic “osteoporosis” fracture. Instead it represents an insufficiency fracture, which means that the bone in this high stress area was not able to maintain its weight-bearing load.
With osteomalacia, the amount of bone is usually normal but the amount of mineral is too low. The bone mineral density measured by DXA will be low, not because of too little bone like in osteoporosis, but due to poor mineralization of the bone. Once vitamin D is increased and calcium is absorbed, the bone will become mineralized again. The next time Gwyneth has a DXA scan, it is likely to show a large improvement in her bone mineral density.
The take-home message is this: Just because you have low bone mass and have experienced a fracture does not mean it is due to osteoporosis. You need to think about other causes. In Gwyneth's case, she had vitamin D deficiency. True, her diet could have contributed to low vitamin D. However, it is more likely that the main factors were living in England without sufficient sunshine year round and not taking supplements.
Bottom line: Stay bone healthy with a sensible diet and enough vitamin D and calcium each day.
Muscle and Muscle Strength
Rickets and osteomalacia are associated with decreased muscle strength. Recently, it was recognized that people with low vitamin D levels have weaker muscles. This muscle weakness is a more subtle consequence of low vitamin D. Vitamin D acts directly on muscle. Treatment with vitamin D increases the size and number of individual muscle fibers that leads to improved physical performance.
Poor muscle function associated with low vitamin D is not just a problem for older adults; it is a problem for people of all ages. A group of almost one hundred young adolescent girls in England were instructed to hop as fast and as hard as possible. They hopped on a special platform that recorded their jumping power, jump height, and speed. Those with low vitamin D generated less power as well as less jump height and speed than those with higher vitamin D levels. Vitamin D is important along with exercise to keep your muscles strong.
Falls
Weaker muscles, particularly weaker quadriceps or thigh muscles predispose you to falling. Dr. Heike Bischoff-Ferrari, a leading researcher in the role of Vitamin D in aging and musculoskeletal health and head of clinical research at University Hospital in Zurich, Switzerland, showed that in a mere three months, supplementation of vitamin D made a large impact on the risk of falling in frail elderly women. She and her colleagues at the University of Basel, Switzerland, studied 122 elderly women residing in a nursing home. Over three months, half were given 800 IU of vitamin D plus 1,200 mg of calcium and the other half received only the 1,200 mg of calcium. For those on calcium plus vitamin D, vitamin D levels were increased and falls were reduced by half in comparison with the calcium only group. In addition, there were improvements in tests of muscle strength.
This was a major new insight and exciting news to me as a geriatrician. To think that by simply giving vitamin D to nursing home residents their rates of falls would decrease! What a boon for these patients' health.
In 2004, Dr. Bischoff-Ferrari published in the Journal of the American Medical Association a meta-analysis that assessed the overall effectiveness of vitamin D to prevent falls. This analysis included five randomized placebo-controlled studies (the most valid kind) with over 1,200 elderly men and women who were treated with vitamin D versus an imitation placebo pill. The risk of falling was reduced by 22 percent.
In 2006, Dr. Bischoff-Ferrari and her colleagues reported the results of their three-year clinical trial of healthy men and women ages sixty-five years and older. Half of the group received 700 IU of vitamin D plus 500 mg of calcium and the other half took imitation pills. Falls were reduced in all women by almost half. An even greater reduction in falls was observed in a subgroup of women who were less physically active. No effect was observed in men. In older women not considered to be at particularly high risk for falling, improving vitamin D resulted in a significant reduction in falls.
Improved muscle strength and lower risk of falling are added benefits of vitamin D. Unfortunately, this research has not been translated consistently into clinical practice. The most vulnerable individuals for falling and fracture are our seniors, particularly those residing in long-term care facilities or those who are homebound. Checking vitamin D levels and providing appropriate vitamin D supplementation is not consistently done in this high-risk group. Think of the healthcare dollars that could be saved by decreasing falls and hip fractures with the simple use of vitamin D. Instead, because more testing has been done recently, some Medicare carriers are actually limiting the testing of vitamin D levels.
Other Diseases: Beyond Bone
Recently, there have been numerous reports about the role of low levels of vitamin D in contributing to other serious health problems beyond bone. Actually, this area has been evolving over about the past thirty years. Only now has it reached a critical mass based on new discoveries.
When I first arrived at the University of California, San Diego, I regularly passed by the office of Dr. Cedric Garland but noticed he was never there. Who was this mystery professor? “Oh, he is one of the Garland brothers,” I was told. “He and his brother, Frank, are ‘the vitamin D guys.'” They had shown an association of vitamin D with colon cancer. Their original paper was published in 1980 by the International Journal of Epidemiology. The opening sentence was: “It is proposed that vitamin D is a protective factor against colon cancer.”
They had observed that when deaths from colon cancer in Caucasian men were plotted on a map of the US, there were many more dots in the northern states than in the southern ones. They examined a variety of different possibilities to explain this observation. They estimated the amount of sunlight reaching the ground for each state based on data from the US Weather Bureau and then overlaid the solar radiation information on the map with colon cancer deaths. Bingo! The highest colon cancer deaths occurred in places that had the lowest amounts of sunlight.
Twenty-five years later, their paper was republished along with recent cellular and molecular research that supported their original observation. A commentary in the same journal issue concluded, “The worms are at last wriggling out of the can that the Garlands opened 25 years ago.”
Over the last few years, it has been more like a volcanic eruption of information. More diseases have been linked to low vitamin D including breast cancer, prostate cancer, ovarian cancer, non-Hodgkin's lymphoma, diabetes, multiple sclerosis, inflammatory bowel disease, rheumatoid arthritis, osteoarthritis, influenza, hypertension, heart failure, heart attacks, stroke, and even premenstrual syndrome (PMS). Wow, it seems like all the major diseases that are leading causes of death are in that list, and every time you turn around another is reported. Flu and influenza were the latest associated diseases reported. Could vitamin D be the next “panacea”?
Caution! For all these diseases and conditions, you need to keep in mind that these are still observations. The type of research study is key to determine what type of conclusions can be drawn from the data. There is strong cause and effect evidence for vitamin D and bone health based on clinical trials. For the most part, no clinical trials have been done for the other diseases. Therefore, so far, one cannot make the leap to cause and effect. Vitamin D and other diseases are still just “associations” without proven cause and effect.
It was thought that only the kidney was capable of producing active vitamin D. So far, researchers have found many other tissues, including cells in the breast, prostate, and colon that have the enzyme needed to produce active vitamin D. However, these tissues produce only local concentrations of active vitamin D. You may see the word “paracrine” used to describe this function, which means that the vitamin D acts locally and does not enter the blood stream. In contrast, active vitamin D produced by the kidney circulates in the blood to affect other organs and tissues and therefore is designated “endocrine.”
In addition, vitamin D receptors seem to be ubiquitous and have been identified in more than forty tissues so far. Cells in these tissues may produce biologic responses. If enough active vitamin D is present, the cell “machinery” works smoothly. If there are inadequate amounts of vitamin D to attach to the receptors, the system breaks down. That is the basis of thinking for how low vitamin D could cause or contribute to the various diseases.
It is amazing though to think that vitamin D may have such far-reaching effects. However, at the moment, some people come off sounding like “snake oil salesmen,” making claims that vitamin D can prevent everything. The panacea of vitamin D effects may be likened to the early days of research into vitamin C. At the time, science was just discovering the many benefits of vitamin C, and some were overplayed while others turned out to be totally validated. The science is evolving. More research is needed to provide the cause and effect link. Stay tuned. It is an exciting time and a plethora of research is underway looking at practically every organ system and disease state.
THE NEXT STEP
As you have read, a multitude of factors can sabotage your ability to get enough vitamin D. Because of that, the amount of vitamin D required to maintain a level over 30 ng/ml will be different if you are young, petite, fair-skinned, and live in Arizona versus being older and residing in Detroit. In general, the average person taking an average supplemental dose of 2,000 IU daily will achieve an average blood level above 30 ng/ml. There is a lot of individual variability! Not everyone can be above average such as the children in Lake Wobegon, author Garrison Keillor's fictional Minnesota town in A Prairie Home Companion. Remember that average means that some people will be lower than the average and others will be higher.
Talk with your doctor about whether you are at high risk for low vitamin D and may need to check your vitamin D level (25-hydroxy or 25-OH vitamin D). If you are not at high risk and have not had your vitamin D level measured, you may take from 800 to 2,000 IU a day of supplemental vitamin D based on your individual circumstances. Many people observe that they feel “better” after increasing their vitamin D, even though they felt “well” with a low vitamin D level.
The general measures of regular exercise and adequate calcium and vitamin D are essential for bone and muscle health for everyone. However, if you are at high risk for fracture or already have osteoporosis, those general measures may not be enough to prevent fractures. You will need to consider adding specific therapies for prevention and treatment of osteoporosis. The next section will cover those options.