Understanding What Vitamins Your Body Needs

For optimum health, your body requires at least 11 vitamins: vitamin A, vitamin D, vitamin E, vitamin K, vitamin C, and the members of the B vitamin family — thiamin (vitamin B1), riboflavin (B2), niacin, vitamin B6, folate, and vitamin B12. Two more B vitamins (biotin and pantothenic acid) and one unusual compound (choline) are also valuable.

Although your body needs these 11 vitamins, it’s amazing how little of each vitamin you need. In some cases, the Recommended Dietary Allowances (RDAs) may be as small as several micrograms — images , or one–one-millionth of a gram.

THE FATHER OF ALL VITAMINS: CASIMIR FUNK

Vitamins are so much a part of modern life that you may have a hard time believing they were first conclusively identified and defined less than a century ago. Of course, people have long known that certain foods contain something special. For example, nearly 4,000 years ago, the Egyptian King Amenophis IV consumed liver to help him see clearly when the light was poor; 2,000 years later, the Greek physician Hippocrates prescribed raw liver soaked in honey for nyctalopia (“night blindness”).

By the end of the 18th century (1795), British Navy ships carried a mandatory supply of limes or lime juice to prevent scurvy among the men on long journeys, thus earning the Brits once and forever the nickname “limeys.” The Japanese, whose sailors had similar problems with beriberi (from biribiri, the word for weak in Sinhala, a language spoken in Sri Lanka), protected their men by adding whole grain barley to the normal ship’s rations.

Everyone knew these remedies worked, but no one knew why until the turn of the 20th century when Casimir Funk, a Polish biochemist working first in England and then in the United States, identified “somethings” in food that he called vitamines (vita = life; amines = nitrogen compounds).

The following year, Funk and a fellow biochemist, Briton Frederick Hopkins, suggested that some medical conditions, such as scurvy and beriberi, were simply deficiency diseases caused by the absence of a specific nutrient in the body. Adding a food with the missing nutrient to one’s diet would prevent or cure the deficiency disease. What else is there to say except Eureka! (which, because Funk was Polish but working in England, is probably exactly what he said).

Modern nutrition classifies vitamins as either fat soluble or water soluble, meaning that they dissolve either in fat or in water. If you consume larger amounts of fat-soluble vitamins than your body needs, the excess is stored in body fat. With water-soluble vitamins, your body simply shrugs its shoulders, so to speak, and urinates away most of the excess.

Each entry on the following list of vitamins names a food serving that provides at least one-quarter of the adult RDA for the particular vitamin. For a complete list of RDAs, check out Chapter 3.

Fat-soluble vitamins

Vitamins A, D, E, and K have two characteristics in common: All dissolve in fat, and all are stored in your fatty tissues. But like members of any family, they also have distinct personalities. One keeps your skin moist. Another protects your bones. A third keeps reproductive organs purring happily. And the fourth enables you to make special proteins. And, yes, as noted late in this chapter, each vitamin may have more than one benefit to offer.

Medical students often use mnemonic (pronounced neh-mah-nic) devices — memory joggers — to remember complicated lists of body parts and symptoms of diseases. Here’s one to help you remember which vitamins are fat soluble: “All Dogs Eat Kidneys,” which stands for vitamins A, D, E, and K, of course.

Vitamin A

Vitamin A is the moisturizing nutrient that keeps your skin and mucous membranes (the slick tissue lining of the nose, mouth, throat, vagina, urethra, and rectum) smooth and supple. Vitamin A is also the vision vitamin, a constituent of 11-cis-retinol, a protein in the rods (cells in the back of your eye that enable you to see even when the lights are low) that prevents or slows the development of age-related macular degeneration, or progressive damage to the retina of the eye, which can cause the loss of central vision (the ability to see clearly enough to read or do fine work). Finally, vitamin A promotes the growth of healthy bones and teeth, keeps your reproductive system humming, and encourages your immune system to churn out the cells you need to fight off infection.

Your body gets its vitamin A from two classes of chemicals:

Retinoids are compounds whose names all start with ret: retinol, retinaldehyde, retinoic acid, and so on. These fat-soluble substances are found in several foods of animal origin: liver (again!) and whole milk, eggs, and butter. Retinoids give you preformed vitamin A, the kind of nutrient your body can use right away.
Carotenoids are vitamin A precursors, chemicals such as beta carotene — a deep yellow carotenoid (pigment) found in dark green, bright yellow, and orange fruits and vegetables. Your body transforms a vitamin A precursor into a retinol-like substance. So far, scientists have identified at least 500 different carotenoids. Only 1 in 10 — about 50 altogether — are considered to be sources of vitamin A.

One-half cup dried apricots or ¼ cup cooked carrots provides 25 percent of the adult RDA for vitamin A.

OVERDOSE BY ACCIDENT

As the great lexicographer and essayist Samuel Johnson, or English naturalist John Ray, Saint Bernard of Clairvaux, or Publius Vergilius Maro, better known as the Roman poet Virgil, or maybe even the author of Ecclesiastes 21:10 (King Solomon?) once wrote: “The road to hell is paved with good intentions.”

Although no one’s really sure who said it first, clearly everyone knows they were talking about life choices. But they may as well have been talking about vitamin A.

A 2014 report from the Environmental Working Group, a nonprofit environmental research organization based in Washington, D.C., suggests that while fewer than half of all American teenagers get an adequate amount of vitamin A each day, the situation with younger kids is exactly opposite. For them, fortifying baby foods with extra vitamin A has led to symptoms of high-dose toxicity that include brittle nails, hair loss, fever, and headache.

Adults who overdose on supplemental vitamin A (or consistently gorge on vitamin A–rich foods such as liver) may experience a reduction in bone density leading to an increased risk of fracture, which is why the RDAs for vitamin A were dramatically lowered several years ago.

Fortification is still the rule in the United States, but both the German Federal Institute for Risk Assessment and the Dutch National Institute for Public Health have proposed there be no vitamin A fortification of foods at all.

Vitamin D

Calcium is essential for hardening teeth and bones, but no matter how much calcium you consume, without vitamin D, your body can’t absorb and use the mineral. Researchers at the Bone Metabolism Laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston say vitamin D may also reduce the risk of tooth loss by preventing the inflammatory response that leads to periodontal disease, a condition that destroys the thin tissue (ligaments) that connects the teeth to the surrounding jawbone.

Vitamin D may also offer protection against some forms of cancer. In February 2006, a report in The American Journal of Public Health suggested that vitamin D supplements halve a person’s risk of developing some forms of cancer, including cancer of the colon, breast, or ovaries. Two years later, data from a study at Boston’s Dana-Farber Cancer Institute suggested that high blood levels of the vitamin prior to chemotherapy prolonged survival in patients with metastatic cancer of the colon.

Vitamin D occurs in three forms:

Calciferol is found naturally in fish oils and egg yolk. In the United States, it’s added to margarines and milk.
Cholecalciferol is created when sunlight hits your skin and ultraviolet rays react with steroid chemicals in body fat just underneath.
Ergocalciferol is synthesized in plants exposed to sunlight. Cholecalciferol and ergocalciferol justify vitamin D’s nickname: the Sunshine Vitamin.

The RDA for vitamin D is measured either in International Units (IUs) or micrograms (mcg) of cholecalciferol: 10 mcg cholecalciferol = 400 IU vitamin D.

One 8-ounce cup of fortified whole milk provides 100 IU, 25 percent of the RDA; one cup of skim milk with added non-fat milk solids has 120 IU.

Vitamin E

Vitamin E, which maintains your healthy reproductive system, nerves, and muscles, is found in tocopherols and tocotrienols, two families of naturally occurring organic chemicals in vegetable oils, nuts, whole grains, and green leafy vegetables.

Tocopherols, the more important source, are anticoagulants and antioxidants that reduce the blood’s ability to clot. As a result, for a while, many people believed that vitamin E was the nutrient specifically designed to ward off blood clot–related heart attacks. But in 2005, data from the Heart Outcomes Prevention Evaluation (HOPE), a study with more than 9,000 at-risk subjects, showed no such vitamin E benefits. And to add insult to injury, patients taking 400 International Units (IU) of vitamin E per day were more likely to develop heart failure.

On the other hand, in 2013, researchers at the Minneapolis VA Health Care System reported that over a period of two to three years, Alzheimer’s patients who got vitamin E experienced a slower loss of the ability to perform simple tasks, such as shopping for food and cooking dinner, than did patients taking memantime (Nemanta), a drug known to preserve nerve function for people with Alzheimer’s, or a placebo. The result, of course, must be confirmed with further studies. (See Chapter 24 for more information on food and your brain.)

One cup of cooked greens, such as mustard greens or kale, provides about 25 percent of the adult RDA for vitamin E.

Vitamin K

Vitamin K is a group of chemicals that your body uses to make specialized proteins found in blood plasma (the clear fluid in blood). One such protein is prothrombin, the protein chiefly responsible for blood clotting. Like vitamin D, vitamin K is essential for healthy bones, activating at least three different proteins that take part in forming new bone cells. In 2003, a report from the long-running Framingham (Massachusetts) Heart Study showed adults consuming the least vitamin K each day are likely to have the highest incidence of broken bones.

Vitamin K is found in dark green leafy vegetables (broccoli, cabbage, kale, lettuce, spinach, and turnip greens), cheese, liver, cereals, and fruits.

There is no RDA established for vitamin K because most of what you need is produced by naturally resident colonies of friendly bacteria in your intestines (the microbiome described in Chapter 2).

Water-soluble vitamins

The good news about water-soluble vitamins is that it’s virtually impossible to overdose on them without taking enormous amounts of supplements. The bad news is that you have to take enough of these vitamins on a more or less regular schedule to protect yourself against deficiencies. But the more good news is that you don’t have to take them every day; you can take less one day and more the next, and it evens out over time.

Vitamin C

Vitamin C, also known by its chemical name ascorbic acid, is essential for the development and maintenance of connective tissue (the fat, muscle, and bone framework of the human body). Vitamin C speeds the production of new cells in wound healing, protects your immune system, helps you fight off infection, reduces the severity of allergic reactions, and plays a role in the syntheses of hormones and other body chemicals.

One medium-size orange or sweet potato provides at least 25 percent of the adult RDA for vitamin C.

LEMONS, LIMES, ORANGES — AND BACON?

Check the meat label. Right there it is, plain as day — vitamin C in the form of sodium ascorbate and/or isoascorbate.

Processed meats, such as bacon and sausages, are preserved with sodium nitrite, which protects the meat from Clostridium botulinum, microorganisms that cause the potentially fatal food poisoning known as botulism.

On its own, sodium nitrite reacts at high temperatures with compounds in meat to form carcinogens called nitrosamines. Antioxidant vitamin C prevents the chemical reaction. It also helps prevent free radicals (incomplete pieces of molecules) from hooking up with each other to form damaging compounds — in this case, carcinogens, substances that cause cancer.

And that is why the U.S. Food and Drug Administration (FDA) and Department of Agriculture/Food Safety and Inspection Service (USDA FISIS) require vitamin C in your bacon.

Thiamin (vitamin B1)

This sulfur (thia) and nitrogen (amin) compound, the first of the B vitamins to be isolated and identified, helps ensure a healthy appetite. It acts as a coenzyme (a substance that works along with other enzymes) essential to at least four different processes by which your body extracts energy from carbohydrates. It’s found in every body tissue, with the highest concentrations in your vital organs — heart, liver, and kidneys.

The richest dietary sources of thiamin are unrefined cereals and grains, lean pork, beans, nuts, and seeds. Refined (“white”) flours, stripped of the brown parts that contain thiamin, are popular in the United States. To make up what’s lost in processing, all breads and cereals are enriched with additional B1.

Three ounces of pork, ham, or beef or pork liver provide at least 25 percent of the adult RDA for thiamine.

Riboflavin (vitamin B2)

Riboflavin, the second B vitamin to be identified, is named for its chemical structure, a carbon-hydrogen-oxygen skeleton that includes ribitol (a sugar) attached to a flavonoid (a substance from plants containing one of the orange-to-red pigments called flavones).

Like thiamin, riboflavin is a coenzyme that enables you to digest and use proteins and carbohydrates. Like vitamin A, it protects the health of mucous membranes. And like the other B vitamins, your best source for riboflavin are foods of animal origin (meat, fish, poultry, eggs, and milk), plus brewer’s yeast, and whole or enriched grain products.

Three ounces of beef or pork liver or one ounce of liverwurst provide 25 percent of the adult RDA for riboflavin. Three ounces of fortified ready-to-eat puffed rice cereal, 163 percent of the RDA for a woman, 138 percent for a man.

Niacin (vitamin B3)

Niacin is found either as a preformed nutrient or acquired via your body’s conversion of the amino acid tryptophan. Preformed niacin comes from meat; tryptophan comes from milk and dairy foods. There is some niacin in grains, but your body can’t absorb it efficiently unless the grain has been treated with lime (the mineral, not the fruit), a practice common in Central and South American countries where lime is added to cornmeal in making tortillas. In the United States, breads and cereals are routinely fortified with niacin.

Three-fourths ounce of turkey or 1.4 ounces of fish provide 25 percent of the adult RDA for niacin.

Pantothenic acid (vitamin B5)

Pantothenic acid is employed in enzyme reactions that enable you to use carbohydrates and create steroid biochemicals such as hormones. This vitamin also helps stabilize blood sugar levels, defends against infection, and protects hemoglobin (the protein in red blood cells that carries oxygen through the body) as well as nerve, brain, and muscle tissue.

You get pantothenic acid from meat, fish, poultry, beans, whole grain cereals, and fortified grain products.

There is no RDA for pantothenic acid. About 1.25 ounces of shitake mushrooms or oily fish provide 25 percent of the adult Adequate Intake (AI).

Vitamin B6 (pyridoxine)

Vitamin B6 is a compound comprising three related chemicals: pyridoxine, pyridoxal, and pyridoxamine. A component of enzymes that metabolize proteins and fats, vitamin B6 is essential for extracting energy and nutrients from food. It also helps lower blood levels of homocysteine (see Chapter 7), an amino acid produced when you digest proteins.

The best food sources of vitamin B6 are liver, chicken, fish, pork, lamb, milk, eggs, unmilled rice (rice with the bran intact), whole grains, soybeans, potatoes, beans, nuts, seeds, dark green vegetables (such as turnip greens), and enriched grain products.

One-third cup of instant (fortified) oatmeal, 3.5 ounces skinless chicken breast or 3 ounces of beef liver provide 25 percent of the RDA for vitamin B6.

Biotin (vitamin B7)

Biotin is a component of enzymes that ferry carbon and oxygen atoms between cells. It helps you metabolize fats and carbohydrates and is essential for synthesizing fatty acids and amino acids needed for healthy growth.

The best food sources of biotin are liver, egg yolk, yeast, nuts, and beans, but if your diet doesn’t give you all the biotin you need, bacteria in your gut will synthesize enough to make up the difference.

There is no RDA for biotin. Two ounces of salmon provide 25 percent of the adult Adequate Intake (AI).

Folic acid (vitamin B9)

Folic acid, also known as folate or folacin, plays a role in the synthesis of DNA, the metabolism of proteins, and the subsequent synthesis of amino acids used to produce new body cells and tissues and is directly involved in both normal growth and wound healing. This vitamin is most important for women of child-bearing age. Not only does it assist in creating new maternal and fetal tissue, an adequate supply before and during pregnancy dramatically reduces the risk of neural tube (spinal cord) birth defects such as spina bifida (the failure of the bones of the spine to close properly around the spinal cord).

Beans, dark green leafy vegetables, liver, yeast, and various fruits are excellent food sources of folate, and as a protective measure, all multivitamin supplements and all grain products sold in the United States must now include 400 micrograms of folate per dose/serving.

A 3.5-ounce serving of Romaine lettuce provides 136 micrograms.

Vitamin B12 (cyanocobalamin)

Vitamin B12 is unique. It’s the only vitamin that contains a mineral — in this case, cobalt, the cobal in its name. The combination is vital for healthy red blood cells and protects myelin, the fatty material that covers your nerves and enables you to transmit electrical impulses (messages) between nerve cells that make it possible for you to see, hear, think, move, and do all the things a healthy body does each day.

The best natural sources of B12 are from animals: beef, pork, poultry, and fish. Fruits and veggies don’t manufacture vitamin B12, but, like vitamin K, this nutrient is produced by beneficial bacteria (the microbiome) in the small intestine.

Three ounces of beef, pork, poultry, or fish provide 25 percent of the adult RDA for vitamin B12.

Choline

In 1998, 138 years after choline was first identified, the Institute of Medicine (IOM) finally declared it essential for human beings. The IOM had good reasons for doing so. Although choline is neither vitamin, mineral, protein, carbohydrate, nor fat, it does help keep body cells healthy.

Choline is used to make acetylcholine, a chemical that enables brain cells to exchange messages. It protects the heart and lowers the risk of liver cancer. And new research at the University of North Carolina (Chapel Hill) shows that choline plays a role in developing and maintaining the ability to think and remember, at least among rat pups and other beasties born to lab animals that were given choline supplements while pregnant. Follow-up studies showed that prenatal choline supplements helped the animals grow bigger brain cells. As yet, no one knows whether this would also be true for human babies.

There is no RDA for choline; ¾ ounce of caviar provides the adult Adequate Intake (AI). Rarely indulge in caviar? Not to worry: One egg gives you 25 percent of the AI.

HAND IN HAND: HOW VITAMINS HELP EACH OTHER

All vitamins have specific jobs in your body. Some have partners. Here are some examples of nutrient cooperation:

Vitamin E keeps vitamin A from being destroyed in your intestines.
Vitamin D enables your body to absorb calcium and phosphorus.
Vitamin C helps folate build proteins.
Vitamin B1 works in digestive enzyme systems with niacin, pantothenic acid, and magnesium.

Taking vitamins with other vitamins may also improve body levels of nutrients. For example, in 1993, scientists at the National Cancer Institute and the U. S. Department of Agriculture (USDA) Agricultural Research Service gave one group of volunteers a vitamin E capsule plus a multivitamin pill; a second group, vitamin E alone; and a third group, no vitamins at all. The people getting vitamin E plus the multivitamin had the highest amount of vitamin E in their blood — more than twice as high as those who took plain vitamin E capsules.

Sometimes, one vitamin may even alleviate a deficiency caused by the lack of another vitamin. People who do not get enough folate are at risk of a form of anemia in which their red blood cells fail to mature. As soon as they get folate, either by injection or by mouth, they begin making new healthy cells. That’s to be expected. What’s surprising is the fact that anemia caused by pellagra, the niacin deficiency disease, may also respond to folate treatment.

Too Much or Too Little: Avoiding Two Ways to Go Wrong with Vitamins

Recommended Dietary Allowances (RDAs) and Adequate Intakes (AIs) are broad enough to prevent vitamin deficiencies and avoid the side effects associated with very large doses of some vitamins. The trick is to get exactly what you need — no more, no less.

Vitamin deficiencies

Vitamin deficiencies are rare among people who have access to a wide variety of foods and know how to put together a balanced diet. For example, the only people likely to experience a vitamin E deficiency are premature and/or low-birth-weight infants or people with a metabolic disorder that keeps them from absorbing fat. A healthy adult may go as long as ten years on a vitamin E-deficient diet without developing any signs of a problem.

Aha, you say, but what about a subclinical deficiency that might sneak up on you? Nutritionists use the term subclinical deficiency to describe a deficit not yet far enough advanced to produce obvious symptoms. In lay terms, however, the phrase has become a handy explanation for common but hard-to-pin-down symptoms, such as fatigue, irritability, nervousness, emotional depression, allergies, and insomnia. And it’s a dandy way to increase the sale of nutritional supplements.

Simply put, the RDAs protect you against deficiency. If your symptoms linger even after you take reasonable amounts of vitamin supplements, something other than a lack of any one vitamin may be to blame. Don’t wait until your patience or your bank account has been exhausted to find out. Check with your doctor. While you’re waiting for an appointment, check out Table 10-1 for a list of the symptoms of various vitamin deficiencies.

Table 10-1 What Happens When You Don’t Get the Vitamins You Need

A Diet Low in This Vitamin …	… May Produce These Signs of Deficiency
Vitamin A	Poor night vision; dry, rough, or cracked skin; dry mucous membranes including the inside of the eye; slow wound healing; nerve damage; reduced ability to taste, hear, and smell; inability to perspire; reduced resistance to respiratory infections
Vitamin D	In children: rickets (weak muscles, delayed tooth development, and soft bones, all caused by the inability to absorb minerals without vitamin D); in adults: osteomalacia (soft, porous bones that fracture easily); fatigue Recent reports suggest that a vitamin D deficiency may reduce a woman’s chances of conceiving while undergoing In Vitro Fertilization (IVF) and increase the risk of asthma attacks in adults.
Vitamin E	Inability to absorb fat
Vitamin K	Blood fails to clot
Vitamin C	Scurvy (bleeding gums; tooth loss; nosebleeds; bruising; painful or swollen joints; shortness of breath; increased susceptibility to infection; slow wound healing; muscle pains; skin rashes)
Thiamin (vitamin B1)	Poor appetite; unintended weight loss; upset stomach; gastric upset (nausea, vomiting); mental depression; an inability to concentrate; fatigue, and the thiamine deficiency disease beriberi
Riboflavin (vitamin B2)	Inflamed mucous membranes, including cracked lips, sore tongue and mouth, burning eyes; skin rashes; anemia; fatigue
Niacin (vitamin B3)	Pellagra (diarrhea; inflamed skin and mucous membranes; mental confusion and/or dementia); fatigue
Vitamin B6 (pyridoxine)	Anemia; convulsions similar to epileptic seizures; skin rashes; upset stomach; nerve damage (in infants); fatigue
Folic acid (vitamin B9)	Anemia (immature red blood cells); fatigue
Vitamin B12	Pernicious anemia (destruction of red blood cells, nerve damage, increased risk of stomach cancer attributed to damaged stomach tissue, neurological/psychiatric symptoms attributed to nerve cell damage); fatigue
Biotin (vitamin B7)	Loss of appetite; upset stomach; pale, dry, scaly skin; hair loss; emotional depression; skin rashes (in infants younger than 6 months)

Vitamin megadoses

Can you get too much of a good thing? Yes. In fact, some vitamins are toxic when taken in the very large amounts popularly known as megadoses. How much is a megadose? Nobody knows for sure. The general consensus is that a megadose is several times the RDA, but the term is so vague that it stops my spellcheck cold and isn’t even in the 28th edition of Stedman’s Medical Dictionary (2006), a tome that’s pretty much the gold standard in medical word books.

Nonetheless, it’s clear that

Megadoses of vitamin A (as retinol) may cause symptoms that make you think you have a brain tumor. Taken by a pregnant woman, megadoses of vitamin A may damage the fetus.
Megadoses of vitamin D may cause kidney stones and hard lumps of calcium in soft tissue (muscles and organs) as well as nausea and other gastro discomfort.
Megadoses of niacin (sometimes used to lower cholesterol levels) can damage liver tissue.
Megadoses of vitamin B6 can cause (temporary) damage to nerves in arms, legs, fingers, and toes.

The important fact is that, with one exception, the likeliest way to get a megadose of vitamins is to take supplements (see Chapter 13 for more on supplements) because it’s pretty much impossible for you to cram down enough food to overdose on vitamins D, E, K, C, and all the Bs.

The exception is vitamin A. Liver and fish liver oils are concentrated sources of preformed vitamin A (retinol), the potentially toxic form of vitamin A. Liver contains so much retinol that early 20th century explorers to the South Pole made themselves sick on seal and whale liver. On the other hand, even very large doses of vitamin E, vitamin K, thiamin (vitamin B1), riboflavin (vitamin B2), folate, vitamin B12, biotin, and pantothenic acid appear safe for human beings. Table 10-2 lists the effects of vitamin overdoses.

Table 10-2 Amounts and Effects of Vitamin Overdoses/Megadoses for Healthy People

Vitamin	Overdose/Megadose and Possible Effect
Vitamin A	15,000 to 25,000 IU retinol a day for adults (2,000 IU or more for children) may lead to liver damage, headache, vomiting, abnormal vision, constipation, hair loss, loss of appetite, low-grade fever, bone pain, sleep disorders, and dry skin and mucous membranes. A pregnant woman who takes more than 10,000 IU a day doubles her risk of giving birth to a child with birth defects.
Vitamin D	2,000 IU a day can cause irreversible damage to kidneys and heart. Smaller doses may cause muscle weakness, headache, nausea, vomiting, high blood pressure, retarded physical growth, mental retardation in children, and fetal abnormalities.
Vitamin E	Large amounts (more than 400 to 800 IU a day) may cause upset stomach or dizziness. Similarly, in 2005 a meta-analysis (a study comparing the results of several studies) in the Annals of Internal Medicine showed that use of “high dose” (400 IU or more) vitamin E supplements might “increase all causes of mortality [death] and should be avoided.”
Vitamin C	1,000 mg or higher may cause upset stomach, diarrhea, or constipation.
Niacin	Doses higher than the RDA raise the production of liver enzymes and blood levels of sugar and uric acid, leading to liver damage and an increased risk of diabetes and gout.
Vitamin B6	Continued use of 50 mg or more a day may damage nerves in arms, legs, hands, and feet. Some experts say the damage is likely to be temporary; others say that it may be permanent.
Choline	Very high doses (14 to 37 times the adequate amount) have been linked to vomiting, salivation, sweating, low blood pressure, and — ugh! — fishy body odor.

Acceptable Exceptions: Taking Extra Vitamins as Needed

Some people do need extra vitamins. Who? Maybe you. The RDAs are designed to protect healthy people from deficiencies, but sometimes the circumstances of your life (or your lifestyle) mean that you need something extra. For example, are you taking medication? Do you smoke? Are you on a restricted diet? Are you pregnant? Are you a nursing mother? Are you approaching menopause? Answer yes to any of these questions, and you may be a person who needs larger amounts of vitamins than the RDAs provide.

I’m taking medication

Many valuable medical drugs interact with vitamins. Some drugs increase or decrease the effectiveness of vitamins; some vitamins increase or decrease the effectiveness of drugs. For example, a woman who’s using birth control pills may absorb less than the customary amount of the B vitamins. For more about vitamin and drug interactions, see Chapter 25.

I’m a smoker

Really? Still? Then you should know that you probably have abnormally low blood levels of vitamin C. More trouble: Chemicals from tobacco smoke create more free radicals in your body. Even the National Research Council, which is tough on vitamin overdosing, says that regular smokers need to take about 66 percent more vitamin C — up to 100 milligrams a day — than nonsmokers.

I never eat animals

Vegans also benefit from extra vitamin C because it increases their ability to absorb iron from plant food. Vitamin B12 enriched grains or supplements are a must to supply the nutrient found only in fish, poultry, milk, cheese, and eggs.

I’m pregnant

Keep in mind that “eating for two” means that you’re the sole source of nutrients for the growing fetus, not that you need to double the amount of food you eat. If you don’t get the vitamins you need, neither will your baby.

The RDAs for many nutrients are the same as those for women who aren’t pregnant. But when you’re pregnant, you need extra

Vitamin D: Every smidgen of vitamin D in a newborn’s body comes from his or her mom. If the mother doesn’t have enough vitamin D, neither will the baby. Are vitamin pills the answer? Yes. And no. The qualifier is how many pills, because although too little vitamin D can weaken a developing fetus, too much can cause birth defects. That’s why until/unless new recommendations for vitamin D are issued, the second important d-word is doctor — as in, check with yours to see what’s right for you.
Vitamin E: To create all that new tissue (the woman’s as well as the baby’s), a pregnant woman needs an extra 2 milligram alpha-tocopherol equivalents (mg alpha-TE) each day, the approximate amount in one egg.
Vitamin C: The level of vitamin C in your blood falls as your vitamin C flows across the placenta to your baby, who may — at some point in the pregnancy — have vitamin C levels as much as 50 percent higher than yours. So you need an extra 10 milligrams of vitamin C each day (½ cup cooked zucchini or two stalks of asparagus).
Riboflavin (vitamin B2): To protect the baby against structural defects, such as cleft palate or a deformed heart, a pregnant woman needs an extra 0.3 milligrams of riboflavin each day (slightly less than 1 ounce of ready-to-eat cereal).
Folate: As many as 2 of every 1,000 babies born each year in the United States have a neural tube defect such as spina bifida because their mothers didn’t get enough folate to meet the RDA standard. Taking 400 micrograms of folate (also known as folic acid) daily before becoming pregnant and through the first two months of pregnancy significantly lowers the risk of giving birth to a child with cleft palate. Taking 400 micrograms of folate each day through an entire pregnancy reduces the risk of neural tube defects.
Vitamin B12: To meet the demands of the growing fetus, a pregnant woman needs an extra 0.2 micrograms of vitamin B12 each day (just 3 ounces of roasted chicken).

I’m breast-feeding

You need extra vitamin A, vitamin E, thiamin, riboflavin, and folate to produce sufficient quantities of nutritious breast milk, about 25 ounces or 750 milliliters each day. You need extra vitamin D, vitamin C, and niacin as insurance to replace the vitamins you lose — that is, the ones you transfer to your child in your milk.

I’m approaching menopause

There are RDAs and AIs for people 50 and older, but in a country where the population over 80 is growing by leaps and bounds, information about the specific vitamin requirements of older women is as hard to find as, well, information about the specific vitamin requirements of older men. Right now, just about all anybody can say for sure about the nutritional needs of older women is that they require extra calcium to stem the natural loss of bone that occurs when women reach menopause and their production of the female hormone estrogen declines. They may also need extra vitamin D to enable their bodies to absorb and use the calcium.

Gender bias alert! No similar studies are available for older men. But adding vitamin D supplements to calcium supplements increases bone density in older men as well.

I have very light skin or very dark skin

Sunlight transforms fats just under the surface of your skin to vitamin D. So getting what you need should be a cinch, right? Not necessarily. Getting enough vitamin D from sunlight is hard to do when you avoid the sun for fear of skin cancer. Safe solution? A diet with sufficient amounts of the vitamin. But you knew that.

Vitamins for Vim and Vigor