Overt vitamin deficiency diseases, such as pellagra or scurvy, are uncommon in persons who consume a typical North American diet. However, it appears that chronic diseases may be caused by insufficient vitamin intake. For example, cardiovascular disease, cancer, and osteoporosis may be caused, in part, by suboptimal levels of vitamin intake. Randomized evidence from clinical trials shows that the rates of certain clinical disease states decrease when specific vitamins are ingested. Fletcher and Fairfield reviewed clinical evidence on vitamin intake related to chronic disease prevention.
Suboptimal levels of a vitamin are defined as “those associated with abnormalities of metabolism that can be corrected by supplementation with that vitamin.”Folate supplementation can reduce homocysteine levels, for example, even in patients whose serum folate concentrations are normal.
There are three ways to increase vitamin intake. The first is a simple improvement in diet. Although this approach involves individualized patient education, it is, in many ways, better than supplementation with a vitamin pill, because foods contain many substances (such as antioxidants and flavonoids) that are biologically active and may contribute to adequate increases in vitamin intake.
The second method is to fortify various commonly ingested foods with vitamins. Examples of this include the addition of folate to cereals and vitamin D to milk. Some persons, however, are uncomfortable with the addition of chemicals to consumables.
The third option is for patients to take a vitamin supplement. All brands of multivita-mins are quite similar, and many contain minerals. However, calcium is not included in adequate amounts in most multivitamins. Although certain multivitamins are marketed as having superior formulations, the authors do not believe that there is any evidence of bioavailability differences because of the formulation. Patients who should probably take more than one multivitamin per day include the elderly and women of childbearing age. The authors specifically recommend that the elderly take two multivitamins daily or one multivitamin plus extra vitamin B12 and vitamin D (because excess vitamin A is associated with an increase in hip fracture, and extra iron may not be needed). Women who may become pregnant should take a multivitamin plus 400 mcg per day of folate.
Updated information about vitamins is available atwww.cc.nih.gov/ccc/supplements (the National Institutes of Health Web site) and atwww.navigator.tufts.edu (a Tufts University Web site).