Whenever there is mention of bone health or osteoporosis, the response I hear most often is, “Sure, I get my calcium.” Almost everyone is clued in to the fact that calcium is essential for bones. However, this perception does not match the reality of what we are actually doing. The problem is that the majority of adults and children are not getting enough calcium each day.
So why are we doing such a poor job meeting our recommended calcium intake? One contributing factor is that many people do not know how much they or their family members need on a daily basis. Even if the target number is known, without a regular routine to ensure daily calcium, an adequate amount is not achieved. It is estimated that the average American diet provides about 600 to 700 mg of calcium a day.
Everyone Is Missing the Mark
Regardless of age, most Americans do not meet the recommended levels of daily calcium. Taking into account both dietary and supplement sources, Americans are falling short across the board. This figure presents national estimates of the percentage of individuals meeting recommended calcium intake from dietary and supplement sources. The data are based on a representative population group.
Overall, boys and men do better than women. However, for both boys and girls, the dramatic decline in calcium intake during the period of greatest bone building is especially troubling. Only 15 percent of girls and 23 percent of boys age nine to thirteen take in an adequate amount of calcium. And only 13 percent of girls fourteen to eighteen meet the requirement, while 42 percent of boys in this age group do. Just at the time of rapid bone growth, the essential building block of calcium is not being supplied in adequate amounts.
SOURCE: Bailey RL, Dodd KW, Goldman JA. Estimation of total usual calcium and vitamin D intakes in the United States. The Journal of Nutrition. 2010; 140:817-22.
DAILY CALCIUM RECOMMENDATIONS
Calcium provides many vital functions. The daily recommendations have been established primarily on the basis of bone health. By meeting the requirements of bone, the needs of other tissues will also be covered. This is because bone serves as a reservoir of calcium that helps to maintain normal blood levels of calcium.
Calcium by the Numbers: How Much Do You Need?
Recommended daily intakes of calcium are from your food, beverages, and supplements combined. If your diet includes the amount of calcium listed for you, no additional supplementation is needed. Pregnant and breastfeeding women should follow the recommendations for their age group.
| Daily Recommended Dietary Allowance Calcium Intake | ||
| Age in years | Amount in milligrams (mg/day) | Upper Level Intake (mg/day) |
| Infants 0 to 6 months | 200 | 1000 |
| Infants 6 to 12 months | 260 | 1500 |
| Children ages 1 to 3 | 700 | 2500 |
| Children ages 4 to 8 | 1000 | 2500 |
| Children ages 9 to 18 | 1300 | 3000 |
| Adults ages 19 to 50 | 1000 | 2500 |
| Men ages 51 to 70 | 1000 | 2000 |
| Women ages 51 to 70 | 1200 | 2000 |
| Adults ages 71 and older | 1200 | 2000 |
These recommendations factor in the absorption of calcium. Preteens and teens have the highest requirements for calcium even though they also have a higher percentage of calcium absorption. The absorption of calcium also increases during pregnancy and breastfeeding to provide the extra calcium needed for the additional demands of the growing baby. In contrast, calcium absorption decreases with age, so the intake recommendation increases for all adults at age seventy-one and all women after reaching the average age of menopause. Also, keep in mind that adequate vitamin D is needed for optimal calcium absorption.
In the case of calcium, more is not always better. The upper limit of calcium intake is considered the safe upper boundary. Excess calcium ends up in your urine. When you consume too much over a long period, you are at risk for kidney stones and other problems.
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.
Calcium-Rich Foods
About three-quarters of calcium in the US diet comes from milk and dairy products. Common nondairy sources of calcium include almonds, beans, small bony fish like sardines, and a few green vegetables. Other foods fortified with calcium can make substantial contributions to your total calcium intake. Bakery products, such as bread, biscuits, and cakes may be made with calcium-fortified flour. Cereals, tofu, rice, and orange juice are other common fortified foods. You need to check labels carefully because not all of these products are fortified and the calcium content varies widely from brand to brand.
People who are lactose intolerant are unable to break down the lactose sugar in the milk and need to look for other sources of calcium. Many who are lactose intolerant are often able to tolerate other dairy products in small quantities. Also, “lactose-free” milk is widely available. Being lactose intolerant does not affect calcium absorption.
Calcium Daily Value Is 1,000 Milligrams
Reading the “Nutrition Facts” on food products requires some translation. The “Percent Daily Value” often shortened to “% DV” is given for the standard nutrients. Some nutrients have both the numerical quantity and the percent daily value specified. For calcium, only the % DV is given. To get the number of milligrams (mg) of calcium in one serving, you need to calculate it from the % DV.
Look at this example:
The calcium daily value is 1,000 mg: a fact you must know because it is not on the label! The Percent DV on the milk label for 1% low fat milk is 35 percent, so you must multiply 1,000 mg times 35 percent to get 350 milligrams for one serving.
You can actually avoid any calculations by simply adding a “0” to the percent:
35 percent + 0 = 350 milligrams
Why don't the labels just specify the milligrams? Fortunately, there is a push to make labels more explicit so that consumers do not need to do any math.
Don't be lured by package claims of “Good Source of Calcium” without checking the exact amount per serving in the “Nutrition Facts” on the back or side of the product. Plus, the attention-grabbing claims that sound healthy may not translate into actually adding many milligrams of calcium to your daily intake because other nutrients in the food might modify the absorption or bioavailability of the calcium.
Also, the same types of food may have many different amounts of calcium depending on the brand. Cereals are a good example. If you pick up a couple of different brands of raisin bran, you will see a difference. When I checked the cereal aisle at the grocery store in early 2011, I found that a one-cup serving of the raisin bran cereals made by Kellogg and Post contain 2 percent of the daily value of calcium or only 20 mg. In contrast, the same one-cup serving size of Total® Raisin Bran contains 100 percent daily value or 1,000 mg of calcium.
Bioavailability
The low calcium content of common plant sources, including most vegetables, fruits, and cereal grains, makes it difficult to meet your calcium requirements exclusively from nondairy foods. Dark green leafy vegetables are presumed to be good sources of calcium. But the bioavailability of the calcium is what actually determines the amount available for absorption. In general, calcium absorption is inversely related to the oxalate content of the food. If oxalate content is high, absorption is low and vice versa.
Oxalates are natural compounds found primarily in plant-based foods. The role of oxalates in plants is not precisely known. Most vegetables have some oxalates. However, kale, broccoli, and bok choy are essentially free of oxalates. In contrast, spinach, beet greens, and chard have high concentrations of oxalates. Sweet potatoes and okra are intermediate. What does this mean? Spinach, although quite nutritious, is not a good source of calcium. Next time your recipe calls for spinach, try substituting kale.
Even though kale, broccoli, and bok choy are good bioavailable sources of calcium, keep in mind that vegetable sources do not have dense calcium content.
“I eat broccoli.” That's what people tell me all the time to prove that they are getting plenty of calcium. Good, it is a nutritious food. However, one floweret of broccoli provides 5 mg and one stalk provides 15 mg. It takes a lot of broccoli to make a dent in your daily calcium requirements. You cannot just count on broccoli for calcium. It is not enough!
The calcium salts used to fortify foods usually have the same calcium absorption values as milk. The exception is calcium citrate malate, which is found in fortified drinks like orange juice and fruit punch. Its absorption is slightly higher. Therefore, those drinks are good substitutes for milk, but you need to watch the sugar content and make sure that you find foods containing the other key nutrients found in milk, such as protein and vitamin D.
Unfortunately, calcium added to soy milk is not readily available for absorption. Even if your brand is calcium-fortified, do not count that amount toward your daily requirements: soy drinkers, take note!
Food Fight: Milk
Milk is in the middle of a nutrition battlefield. On one side is the public policy for milk or dairy consumption, which recommends three cups a day; on the other side are anti-milk groups who say that no amount of dairy is safe. Some claim that milk actually causes osteoporosis, which definitely turns conventional wisdom on its head. Research provides the data that support the conclusion that milk builds strong bones.
Studies of children with dairy-exclusion diets show lower bone acquisition during growth compared with those who drink milk. The outcomes of dairy-exclusion diets depend on whether other sources of calcium, vitamin D, protein, and other nutrients are replaced in sufficient quantities.
In observational studies, such as the Nurses Health Study, no link was observed between dairy intake and fractures. Other observational studies consistently show that lifetime milk consumption is associated with higher bone density. The majority of intervention studies show that higher amounts of dairy in the diet increase bone density.
Although the science behind milk and bone appears strong, the debate is far from settled. If you choose not to include milk and dairy products, be sure that you get sufficient calcium from other sources.
Caffeine
Although caffeine is regularly reported as harmful, the data are conflicting. Some studies show an increased loss of calcium by the kidney from moderate coffee intake while others studies show no effect. The reason for the differing results may be related to adequate calcium intake, since high caffeine intake is often a marker for low calcium intake.
In the Rancho Bernardo Study, lifetime caffeinated coffee drinking was associated with reduced bone density only when the coffee was not supplemented daily with milk. The negative effect of caffeine on calcium absorption was small enough to be offset by as little as one to two tablespoons of milk. After viewing the results of the Rancho Bernardo Study in 1994, I switched to lattes just to be sure! As with anything else, do not overindulge caffeine.
If you have sufficient calcium, your cup of coffee will not cause excessive losses of calcium. To quote Dr. Robert Heaney, an internationally recognized expert in calcium nutrition and bone biology at Creighton University: “The solution is not to decrease the caffeine intake of the Western world, but to provide adequate sources and intakes of calcium.” That is good news for you coffee drinkers!
Soft Drinks
Soft drinks have been linked to lower bone mass. The caffeine and phosphoric acid content were initially thought to be the culprit. Further studies show that the association is due to displacing milk in the diet. Sugar-sweetened beverages including soft drinks have become a staple in the diets of children and teens. These nutrient-poor beverages displace milk just at the time when children and teens begin to have increased calcium needs for growing bones. Soft drinks may also add to weight problems.
Soft drinks are on the “hit” list for schools, and they are a focus of First Lady Michelle Obama's healthy eating for kids initiative. Data from Project EAT (Eating Among Teens) showed that those who consumed little or no milk gained significantly more weight than their peers who consumed milk.
Variations in genetics may also contribute to the association between milk consumption and bone density. A recent study of genes and low milk intake in teenage girls suggests that higher consumption of milk is needed for certain subgroups based on their vitamin D receptor gene type.
Promote the idea of putting on a “milk mustache” of low-fat milk and other low-calorie, nutrient-dense drinks to children and teens. Limit the availability of other beverages, including fruit juices, sport drinks, power drinks, and soft drinks.
Salt
High fat and high sugar foods are not the only culinary culprits for higher disease risk. Though we hear a lot about salt contributing to high blood pressure, heart attacks, and strokes, you may not realize that too much salt also increases calcium loss, which contributes to bone loss and osteoporosis. Sodium competes with calcium for reabsorption because sodium and calcium share the same transport system in the kidney. As a result, sodium minimizes even the effects of some good sources of calcium, such as processed cheeses.
Our table salt is sodium chloride or “NaCl” in chemical shorthand. Sodium is important for many biologic functions in our bodies. We cannot live without it. However, most of us use too much of it, and this pattern of overuse is hard to break because our taste buds have become accustomed to large quantities of salt in our foods.
The problem is not the salt shaker and those few grains you throw over your shoulder for good luck. The problem is the hidden sources of salt. Even though a food may not taste “salty,” it may have plenty of salt. You may be good about the salt shaker but you need to be a label reader, too.
Unfortunately, labels have plenty of jargon: sodium-free, very low sodium, low sodium, reduced sodium, unsalted, no salt added, or without added salt. Who came up with these classifications that only make your head spin?
Ignore these labels and just go straight to the “Nutrition Facts.” Look at this example from a bag of pretzels.
At least the “Nutrition Facts” give the amount of sodium in milligrams so that you don't have to do math! The current recommended daily value on nutrition food labels is “less than 2,400 milligrams.” Calculations are based on that figure, which is about one teaspoon of salt. However, the report of the Dietary Guidelines for Americans, 2010, estimates that the average daily consumption is 3,400 mg a day for all Americans, ages two and over. The new guidelines reduce daily sodium intake to less than 2,300 mg. For persons who are fifty-one and older, and those of any age who are African American or have hypertension, diabetes, or chronic kidney disease, a further reduction of intake to 1,500 mg is recommended. The 1,500 mg guidelines apply to about half of the US population. About two-thirds of a teaspoon of table salt is equivalent to 1,500 mg of sodium. The highest concentrations of sodium are found in packaged foods, processed meats such as hot dogs and deli meats, canned soups and vegetables, and in many other products. It goes without saying that foods with visible salt are high in sodium—potato chips, corn chips, pretzels, nuts. Though you can get them all unsalted, I agree that without salt potato chips just do not taste the same. Despite the risks involved with overconsumption of sodium, you can eat these foods; just don't make a steady diet of them. The best approach is to substitute another food for the high salt variety. For instance, instead of using salt-laden ready-made rice mix, make your own rice without adding salt to the water.
In fact, manufacturers are trying to come up with ways to decrease the salt in their products. For example, in 2010 the Campbell Soup Company decreased the sodium content in its Original V8 100% Vegetable Juice to 420 mg per eight-ounce glass; still too high, but at least it is moving in the right direction. Apparently, salt helps the consistency of certain foods, and food scientists have so far been unable to find acceptable, palatable substitutions.
Tips for Reducing Salt in Your Diet
The majority of sodium in the diet comes from processed or prepared foods. If you cut down on processed foods and use less salt in food preparation, you will be taking the right steps to help achieve the goal of 1,500 mg of salt a day.
- Read nutrition labels for sodium content.
- If you use canned foods, like beans and tuna, rinse them in water first.
- Substitute fresh or frozen vegetables for canned foods.
- Eat fresh poultry, fish, and lean meats instead of processed versions.
- Substitute herbs, spices, lemon, or vinegar for salt on foods.
- Make your own salad dressings.
- Use lemon juice and olive oil on vegetables.
- Try low-salt versions of sauces that are high in sodium, like soy or barbecue, and use in small amounts.
- Buy low-sodium chicken broth or soups.
- Select unsalted nuts and snacks.
When dining out, have your dressings and sauces served on the side. My favorite Chinese restaurant provides nutrition facts about everything on the menu. The sodium contained in some of the dishes is quite high, and that is before you drizzle soy sauce on your plate. Oh, so you're using the soy sauce with the green top or the label “low sodium”—no worries. Unfortunately, even the low-sodium soy sauce has plenty: 460 mg in one tablespoon. Maybe it does not seem so bad compared with the 1,200 mg of sodium for one tablespoon of the regular soy sauce.
Reducing your salt intake is generally a good thing, but don't go overboard. Taking away too much salt can cause problems with your body's water balance. During my residency training at the Emory University School of Medicine in Atlanta, Georgia, the now late Dr. B. Woodfin (Woody) Cobbs, a respected and well-loved cardiologist at the Emory Clinic, would order potato chips STAT (meaning bring immediately) to the bedside of patients who had been overzealous in restricting salt. However, usually it is a problem of too much rather than too little.
Writing about all this salty food is sending me to the cupboard craving something salty. The good news is that as you reduce the salt content in your diet, your taste buds become accustomed to less salt.
Supplements: Making Up the Difference
Dietary sources of calcium should be your primary way to meet your daily recommended intake. During the preteen and teenage growing years it is especially important to get those 1,300 mg a day. Studies suggest that supplemental calcium may not be as effective as calcium from dietary sources for individuals in this age group. If they rely on supplements, they may be missing many of the added benefits for the growing skeleton, such as protein, that other food sources provide.
If calcium supplements are substituted for dairy products to meet children's calcium needs, attention to other nutrients may be needed. Low calcium intake has been associated with low intake of magnesium and several vitamins, including riboflavin, B-6, B-12, and thiamine. Experts are mixed on supplements for kids. If you do use supplements, use the children's brands.
For adults, the sources do not seem to be as important. While diet is the recommended source of calcium, if you are not meeting your daily goals by diet alone, make it up with supplements. You have many options in terms of type and delivery. Tablets are the most common. Many of you do not like taking tablets. The calcium tablets combined with vitamin D are large tablets. Some can be dissolved in water. There are also other choices: soft chews, liquid, and even sprinkles.
Calcium carbonate is generally the most economical calcium supplement. Most calcium supplements should be taken with meals, although calcium citrate and calcium citrate malate can be taken anytime. The downside of calcium citrate is that the pills are larger and contain less calcium.
It is best to divide the dose of supplemental calcium to maximize absorption; take no more than 500 mg at one time.
Your Turn…
Step 1: Diet
Keep track of how much calcium you are getting in your diet. Do it daily for a typical week. An easy way is to write down everything you eat. Do not forget that protein bar or mineral water. Put a check next to the items that have some calcium content. To estimate the calcium, read the nutrition labels to determine the calcium based on serving size versus how much you are eating. For nonlabeled items like vegetables, estimate from the calcium food sources table (pages 131-32). Add each day's totals. Take an average of your total week.
Step 2: Supplements
Look at all the supplements you are taking. Add up all the calcium. For example, most multivitamins contain a small amount of calcium. Remember: start with identifying the serving size, which is not always one tablet. The number of tablets is the quantity that provides the amounts listed in “Supplement Facts.”
Step 3: Meeting your daily recommended dietary allowance?
Write down your recommended daily calcium target number (refer to “Calcium By the Numbers”). Subtract your average daily dietary calcium and your average supplement use from the total.
Daily recommended target number_________ Example: 1200 mg
Subtract
Average dietary calcium_________ Example: 400 mg
Subtract
Supplemental calcium_________ Example: 500 mg
Equals
Difference__________ Example: 300 mg
What is your result? How did you do?
If you are at or close to zero, keep doing what you are doing. If you are not, make adjustments for too much or too little. In the example, only 300 mg more is needed. You can boost your dietary calcium by adding foods or make up the deficit with a calcium supplement.
Some ideas for increasing dietary calcium include the following.
Breakfast: Add yogurt to your breakfast routine
Snack: A handful of almonds
Lunch: Cheese on your salad or sandwich
Dinner: Beans or bok choy as a side dish
Step 4: Check your family's calcium status
Go back through the first three steps to examine how the rest of your family is doing with getting their daily calcium. Counsel and modify as needed.
Add Up Your Calcium From Diet and Supplements…
What If You Have Had Kidney Stones?
Many people with a history of kidney stones avoid calcium supplements. For most people that is not necessary. In fact, studies show that individuals who both use calcium supplements and have a history of kidney stones actually have a lower rate of new kidney stones than those not taking supplements. I recommend using calcium citrate for those of you with a history of kidney stones although definitive evidence is lacking for choosing one type of supplement over another.
The most common type of kidney stone is calcium oxalate. These stones typically form because of dehydration or a diet high in oxalate-containing foods. Therefore, drinking plenty of water every day is important, as is limiting high-oxalate foods in your diet. Examples of foods high in oxalates include spinach, beet leaves, swiss chard, chives, parsley, and vegetables that can be used as grains, such as amaranth and quinoa.
If you have not had one done, a twenty-four-hour urine collection for calcium to evaluate your risk of stones may be helpful. The urine collection is usually done after you have discontinued taking your calcium supplements and have limited your dietary intake to fewer than 800 mg for one to two weeks. The test will show whether you are losing too much calcium in your urine, which could predispose you to more kidney stones. Low dose of a “water pill” called thiazide diuretic may be helpful to lessen the loss of calcium. Talk with your doctor.
Are Calcium Supplements Harmful to the Heart?
A calcium controversy was stirred up again in 2010 concerning calcium supplements and the risk of heart attacks. Results of a meta-analysis done by New Zealand researchers and released online by the British Medical Journal created a media buzz and sparked widespread concern. The researchers found that 2.7 percent of subjects taking calcium supplements had heart attacks compared with 2.2 percent of those taking placebo tablets However, the study has been criticized for many design flaws.
In contrast, an Australian study (the Calcium Intake Fracture Outcome Study), which was released online about the same time in the Journal of Bone and Mineral Research and received little if any attention, showed no harmful effects. Calcium supplementation of 1,200 mg daily did not increase the risk of heart attacks or strokes in the older women who were followed for almost ten years. A further analysis suggested that calcium supplementation may reduce the risk of hospitalization and death in patients with pre-existing heart disease. More research will be undertaken to investigate this area.
The bottom line is that you should add up calcium from your dietary sources and take just enough calcium supplements to reach your recommended daily amount. For example, if your recommended calcium intake is 1,200 mg and your average dietary calcium intake is 700 mg, you will need 500 mg of calcium supplement, not 1,200 mg. In addition, make sure you are taking sufficient vitamin D. Vitamin D is essential for efficient absorption of calcium.
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The Bare Bones
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