In the News
Vitamins & Minerals
What do they do?
Multiple vitamin-mineral supplements, sometimes known as multivitamin supplements, contain a variable number of essential and/or non-essential nutrients. Their primary purpose is to provide a convenient way to take a variety of supplemental nutrients from a single product in order to prevent vitamin or mineral deficiencies, as well as to achieve higher intakes of nutrients believed to be of benefit above typical dietary levels.
Do multis provide the USRDA?
Many multivitamins contain at least 100% of the Daily Value (DV) or the US Recommended Dietary Allowance (USRDA) of all vitamins that have been assigned these recommended values. Mineral levels may be lower, or in the case of high potency multivitamins, most or all mineral levels may also be at 100% of DV or USRDA. Micronutrients that should be included in a complete multivitamin are vitamin A (or beta-carotene), vitamin B-complex (thiamine, riboflavin, niacin and/or niacinamide, vitamin B6, folic acid (folate), vitamin B12, pantothenic acid, and biotin), vitamin C, vitamin D, and vitamin E, and the minerals calcium, magnesium, zinc, iodine, selenium, copper, manganese, chromium, molybdenum, and possibly iron. Some multivitamins also contain vitamin K, but people taking the medication warfarin (Coumadin) should consult their doctor before taking vitamin K supplements. Phosphorus is another essential dietary mineral, but is so abundant in the diet that it does not need to be included in a multivitamin formula. The only exception is for elderly people, whose diets tend to be lower in phosphorus. Calcium interferes with phosphorus absorption, so older people who are taking a calcium supplement might benefit from taking additional phosphorus.
What else should I know?
Potassium is an unusual case, as adequate amounts of potassium cannot, by law, be sold in nonprescription products. Thus, potassium, when included in a multivitamin formula, represents only a trivial amount. Multivitamins may contain iron, but these should be taken only by people who have been diagnosed as having, or being at high risk of, iron deficiency, or who have a history of frequent iron deficiency.
What may I need more of?
Some nutrients may be beneficial at levels above what is possible to obtain from diet alone, and a multivitamin formula can provide these levels as well. Nutrients that may be useful to most people in larger amounts include vitamin C, folic acid, and calcium. Vitamin E has long been thought to protect against heart disease beginning at 100 IU per day, but more recent research has cast doubt on the value of vitamin E for heart-disease prevention. Large amounts of vitamin B1, vitamin B2, vitamin B3, and pantothenic acid are often included in multivitamin formulas. Some people claim to experience improvements in mood, energy, and/or overall well-being when taking higher-than-RDA amounts of B vitamins. While there is not a great deal of scientific research to support those observations, one double-blind study of healthy volunteers found that a multivitamin supplement significantly reduced anxiety and perceived stress levels, and possibly improved energy and the ability to concentrate.
What about “non-essential” nutrients?
The importance of including the nonessential nutrient beta-carotene in multivitamins remains speculative. The synthetic beta-carotene found in most multivitamins clearly does not prevent cancer and may increase the risk of lung cancer in smokers. Therefore, the inclusion of synthetic beta-carotene in multivitamin formulas is of questionable value, and it should be avoided by smokers. This concern was validated by the results of a large study in which male smokers who supplemented with synthetic beta-carotene had an 18% increase in incidence of lung cancer, compared with those given a placebo. On the other hand, because beta-carotene can be converted to vitamin A without causing vitamin A toxicity, some manufacturers use beta-carotene as a source of vitamin A. In contrast to synthetic beta-carotene, however, natural beta-carotene and several other carotenoids may be helpful in preventing certain diseases, including some cancers, although the safety of natural beta-carotene for smokers has not been demonstrated. Increasingly, natural beta-carotene and several other carotenoids are found in higher quality multivitamins.
Another class of non-essential nutrients is the flavonoids, which have antioxidant and other properties and have been reported by some, though not all, researchers to be linked with a reduced risk of heart disease. Multivitamin supplements also frequently include other nutrients of uncertain benefit in the small amounts supplied, such as choline, inositol, and various amino acids.
What’s most important for kids and for pregnant women?
Preliminary and double-blind trials have shown that women who use a multivitamin containing folic acid, beginning three months before becoming pregnant and continuing through the first three months of pregnancy, have a significantly lower risk of having babies with neural tube defects (e.g., spina bifida) and other congenital defects.
In one double-blind trial, schoolchildren received, for three months, a daily low-potency vitamin-mineral tablet containing 50% of the USRDA for most essential vitamins and the minerals. The subjects were “working class,” primarily Hispanic, children, aged 6 to 12 years. Dramatic gains in certain measures of IQ were observed in about 20% of the supplemented children. These gains may have been due to the correction of specific nutrient deficiencies (for example, iron) found in these children. However, it was not possible in this study to identify which nutrients caused the increases in IQ.
What about “one-per-day” multiples?
One-per-day multiples are primarily B-complex vitamins, with both vitamin A, vitamin C, vitamin D, and vitamin E included either at high or low potency, depending on the supplement. The rest of the formula tends to be low potency. It does not take much of some of the minerals—for example, copper, zinc, and iron—to offer 100% or more of what people normally require, so these minerals may appear at reasonable levels in a one-per-day multivitamin.
One-per-day multivitamins usually do not provide sufficient amounts of many nutrients shown to benefit people eating a Western diet, such as calcium and magnesium. One-per-day multivitamins should therefore not be viewed as a way to “cover all bases” in the way that high-potency multivitamins, requiring three or more pills per day, are viewed.
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