4.9: Dietary Supplements

Many people don’t meet all their RDAs (it’s also true that people who take supplements tend to be those who need them the least). Not knowing whether our diet meets the RDAs, many of us take a multivitamin/mineral pill (the kind with 100% DV) “just in case.” This is reasonable, but still needs to be considered carefully, e.g., most men and postmenopausal women shouldn’t take iron (see Chap. 7). Generally speaking, buy the least expensive pills, e.g., the body doesn’t differentiate between vitamin C made in a lab and that extracted from rose hips—vitamin C is simply vitamin C.

Dietary supplements also include a wide variety of products—from protein powders to herbs—too wide a variety to discuss here. Be extra cautious. Unlike drugs or food additives, dietary supplements don’t have to be proven safe or effective (and may not even contain what they say). A good source of information on dietary supplements: Office of Dietary Supplements: ods.od.nih.gov

You may already get a vitamin/mineral pill in your breakfast cereal or energy bar, e.g., the label says, has 100% DV of 13 vitamins and minerals! Look at the label’s ingredient list and Nutrition Facts section to see what and how much has been added. This is an expensive way to take a supplement. Buying an unfortified brand of the cereal and the vitamin/mineral pills separately saves money, and you’re less likely to overdo it. Many cereals have a pill’s worth sprayed on a serving (about a cup of flakes; about ½ cup of heavier cereal), and some people eat several bowls a day, e.g., college students looking for fast food in empty cupboards.

A pregnant woman who eats several servings of fortified cereal and energy bars in addition to vitamin pills can get several times her RDA of vitamin A—enough to risk a birth defect from excess vitamin A. Fortunately, many products now provide added vitamin A as beta-carotene, which can be converted to vitamin A in the body, if needed, and doesn’t itself cause birth defects. The beta-carotene is listed as %DV vitamin A on the nutrition label, so look for beta-carotene on the ingredient list.

Men who eat iron-fortified food and take iron-containing vitamin/mineral pills can get several times their RDA of iron—enough to worry about a long-term accumulation of iron to toxic levels (see Chap. 7). A few other caveats:

• A nutrient can cure what ails you only if the ailment stems from a deficiency of that nutrient. This seems obvious, but lots of supplements are sold by suggesting they’re the answer to your lack of energy, bleeding gums, etc. Deficiencies can be at fault, but the usual causes are much more mundane (e.g., tired from not enough sleep, bleeding gums from poor dental hygiene) and aren’t helped by supplements. Also, many ailments go away on their own, e.g., an ache that comes and goes. If you get better after taking a supplement, the supplement often gets the credit, whether any credit is due.
• Nutrients at extremely high doses act as drugs rather than nutrients. Huge doses (1,000 to 9,000 mg) of the B-vitamin nicotinic acid (niacin) are used to treat high blood-cholesterol (see Chap. 8) and can have serious side-effects, e.g., liver damage, so should only be used under a physician’s care. The vitamin doesn’t function here as a vitamin (adult RDA is 14 to 16 mg).
• When you hear that a study showed a supplement helped prevent cancer, etc., look more closely at the study before running out to buy a bottle. For example, a study showing that selenium supplements lowered the incidence of cancer was widely publicized (see Chap. 2). The subjects were deficient in selenium because they lived in an area of rural China where the local soil was extremely low in selenium and their diet was almost exclusively locally grown food. Hardly the situation here. Also, too much selenium is toxic, and high soil-selenium is a concern in some parts of the U.S.
• Many studies test supplements only at doses much higher than the RDA, and only focus on one outcome (e.g., cancer). If the supplemented group does better than the placebo group, the unanswered question is whether a smaller dose (the RDA or less)—an amount covered by a good diet—would have been as effective. Studies include people who are deficient in the nutrient and are helped by getting a bit more—again, an amount easily obtained by improved diet. Another unanswered question is whether the nutrient taken in high doses has untoward effects on other aspects of health that weren’t examined.

Food is usually a much better source of nutrients than supplements, but it’s very hard to get people to change their diet—as many of us know from personal experience. One solution has been to add nutrients to foods we already eat, e.g., iron and some B-vitamins added to white flour, vitamins A and D added to milk.

There are, of course, situations where vitamin/mineral supplements or fortified foods are well-advised. It can be hard to meet RDAs on a very low calorie diet, so an inexpensive daily multivitamin/mineral pill is advised when dieting. An estimated 10-30% of those over age 50 have trouble absorbing vitamin B₁₂ from food, so this age group is advised to get most of their B₁₂ from fortified foods or a supplement.

Women capable of becoming pregnant are advised to get their B-vitamin folate RDA from fortified foods or a supplement. The folate RDA is much higher for pregnant women, and a deficiency in early pregnancy raises the risk of certain birth defects.

Staple grains like white flour have been required since 1998 to be fortified with folate. Nutrition experts debated this requirement. The worry was that adding folate to a staple grain may present a risk to older people who may be deficient in vitamin B₁₂.

Large amounts of folate can mask the anemia of vitamin B₁₂ deficiency. This delays the diagnosis of vitamin B₁₂ deficiency, which can lead to permanent nerve damage (see Chap. 6 and 7). Benefit versus risk is always a factor in deciding about fortifying foods or taking supplements.

An advantage of getting nutrients from food rather than supplements is that there are many healthful substances in food that aren’t nutrients, per se, and many of these are yet to be identified. Also, you’re not likely to make mistakes with dosages when you get nutrients from food.

Be a wary consumer—do you really believe that an advertised pill contains the equivalent of 2 stalks of broccoli?