- A diet naturally high in vitamins can be the best defense against many diseases. Fresh fruits and vegetables and whole grains are the primary sources of vitamins, carotenoids, and phytochemicals, as well as of fiber and important minerals.
- Supplements are helpful only in certain situations; for example, pregnant women may benefit from prenatal supplements and many adults benefit from vitamin D supplements.
- The Food and Drug Administration (FDA) does not require manufacturers to provide any scientific evidence that dietary supplements are safe and effective before a product is sold (unlike drugs, which must be proven both safe and effective through clinical trials). If a supplement causes side effects in people once it is for sale, the government may place restrictions on the supplement or withdraw it from the market. The FDA may also withdraw products from the market if their labels are misleading or false.
The Recommended Dietary Allowance (RDA) for vitamins is gradually being replaced by a new standard called the Dietary Reference Intake (DRI). The DRI represents a shift in nutritional emphasis -- from preventing deficiencies to lowering risks of chronic diseases, such as cardiovascular disease.
Vitamins and Health
- Many fresh fruits and vegetables contain chemicals that may fight many cancers, including lung, breast, colon, and prostate cancers.
- Evidence now shows beta-carotene supplements can have harmful effects, at least in smokers, increasing their risk for lung cancer and their overall death rates. Beta-carotene from food appears safe.
- Studies have reported that a diet high in fruits and vegetables containing beta-carotene, lycopene, and other carotenoids may reduce the risk of heart attack. Diets low in lycopene (particularly from tomatoes) have been associated with a significantly higher risk of heart disease and stroke. Supplements, however, do not reduce the risk.
- Carotenoids, especially lutein, lycopene, and zeaxanthin are especially eye-protective and may help prevent cataracts and macular degeneration.
- Studies are mixed as to whether vitamin supplements protect against upper respiratory infections. The weight of evidence suggests there is little or no benefit. It is possible that vitamin C or multivitamin supplements may be helpful in specific people.
Review Date: 10/08/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.