The majority of Americans regularly take a multivitamin, according to the Washington Post. But according to a panel of experts assembled by the Office of Dietary Supplements and the Office of Medical Applications of Research at the National Institutes of Health, research doesn't prove they are beneficial, and they might even be harmful in some cases. Multivitamins have not been studied for long enough to understand risks they might have. However, they have been studied enough for us to know of some of the benefits they contain.
Cancer
A 2007 study in the American Journal of Clinical Nutrition followed a poorly nourished Chinese population and found that supplementation of beta-carotene, vitamin E and selenium at doses one to two times the Recommended Daily Allowance for five years led to13 to 21 percent reductions in gastric cancer incidence, gastric cancer mortality and total cancer mortality. The study also found that smokers who took vitamin E supplements had 32 percent less risk of prostate cancer; 41 percent less risk of prostate cancer mortality and 22 percent less risk of colorectal cancer. Selenium supplements of 200 mcg. per day reduced risk of lung, colorectal, and prostate cancers. Those who used selenium supplements also had a reduced risk of liver cancer.
Vision
The NIH panel stated that vitamins A, C and E and the mineral zinc could prevent some age-related vision loss. The panel cited a study in which participants took 500 mg. of vitamin C; 400 IU of vitamin E; 15 mg. of beta carotene and 80 mg. of zinc each day. The vitamins reduced the risk of developing macular degeneration, an eye disorder that damages the center of the retina, by 25 percent.
Bone Density
Calcium combined with vitamin D supplements may possibly prevent bone fractures, according to the 2007 study in the American Journal of Clinical Nutrition. The NIH panel recommended calcium and vitamin D supplements for post-menopausal women. Women over age 50 should consume 1,200 mg. of calcium each day and 400 IU of vitamin D. Women 70 and older need 600 IU of vitamin D each day.
Folic Acid
All women of childbearing age should take folic acid, on its own or in a multivitamin. Folic acid is a B vitamin that prevents spina bifida and other neural tube birth defects. Women need 400 mcg. daily. Harvard School of Public Health recommends staying away from cereals, protein bars, and other foods that are fortified with folic acid if you take a multivitamin containing folic acid. The multivitamin should contain all you need.
Concerns
The NIH panel warned that because many foods are now fortified with vitamins and minerals, some people who take multivitamins may be getting too much. High doses of certain vitamins and minerals can create adverse effects. High levels of vitamin A, for instance, can increase risk of osteoporosis. Certain multivitamin ingredients also create cause for concern. Excess lung cancer has occurred in asbestos workers and smokers consuming beta-carotene, according to the panel. Vitamin D and calcium may increase the risk of kidney stones in some people. The panel was also concerned that not enough research has been done to determine how multivitamins interact with drugs.
Recommendations
While it's possible to meet your nutritional needs with food alone, most Americans don't. Many adults lack vitamins E, A and C and the minerals calcium, magnesium and potassium. If you do choose to take a multivitamin, pick one that doesn't have more than 100 percent of recommended daily intake of vitamin A. Stay close to recommended doses for other vitamins and minerals in the multivitamin, recommends the Harvard School of Public Health. Avoid mega-dose vitamins.
References
- "Washington Post":Multivitamins, Multi Questions
- Harvard School of Public Health: Vitamins-What Should You Eat?
- "American Journal of Clinical Nutrition"; Multivitamin/Mineral Supplements and Prevention of Chronic Disease: Executive Summary; Han-Yao Huang et al; January 2007.
- National Guideline Clearinghouse: NIH State-of-the-Science Conference Statement on multivitamin/mineral supplements and chronic disease prevention.
- Siteman Cancer Center: Osteoporosis Risk List
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