Three major studies with a total of 426,000 study subjects over the age of 40 showed no difference between those who took and those who didn’t take multi-vitamins as to lifespan or the incidence of cardiovascular disease, cancer, or stroke.
Other studies showed no effect of multi-vitamin use on the incidence of colds, other infections, length of illness, or absence from school, work or other planned activities.
Cognitive performance was not improved in various study groups that took multi-vitamins for 6-12 months
However, the U.S. Dietary Guidelines Advisory Committee found that the following nutrients that are deficient among a large number of Americans:
- Vitamin D
- Folic acid
- Vitamin B-12
- Iron (among women due to menstruation)
- Folic acid: Too little folic acid can increase the risk of colorectal cancer, and pregnant women who are deficient in folic acid are at risk for having babies with neural tube defects. That is why the U.S. government now mandates that folic acid be added to grain products. However, there is some evidence that too much folic acid taken over several years can increase the risk of having colorectal pre-cancerous growths (adenomous polyps) as well as prostate cancer. Thus, it is prudent not to ingest more than 1,000 micrograms a day of folic acid. Some breakfast cereals contain 400 micrograms per serving, and many people eat more than the standard serving size. Eating such cereals every day as well as taking a multivitamin and eating fortified bread, pasta, or rice can easily lead to exceeding 1,000 micrograms. This can be prevented by avoiding multivitamins with more than 400 micrograms of folic acid and limiting consumption of cereals that are fortified with 400 micrograms of folic acid per serving (e.g. Kashi Heart to Heart, Total, Multigrain Cheerios, Kellog’s Mueslix, Product 19, Smart Start, and Special K Original).
- Selenium: Although there is marginal evidence that selenium may lower the risk of certain types of cancer, a study showed that people who took 200 micrograms of selenium daily for 8 years were almost 3 times as likely to be diagnosed with diabetes than those who didn’t take the supplement. So it is best to avoid multivitamins that contain more than 100 micrograms of selenium.
- Vitamin A: While a Vitamin A deficiency can cause various health problems, very few Americans are deficient in the vitamin. However, a study showed that excess Vitamin A (more than 1667 IU/day) doubled the risk of hip fracture among women. The safest alternative is to take a multivitamin that contains beta-carotene rather than Vitamin A. Beta carotene is converted to Vitamin A as needed by the body and doesn’t cause any harm itself.
- Unless you feel you can get all your needed nutrients from your food, take a multivitamin that has 100% of the recommended daily value of each vitamin, rather than taking megadoses.
- It is advisable not to exceed 1000 micrograms per day of folic acid by avoiding multivitamins with over 400 micrograms per serving and limiting intake of breakfast cereals containing more than 200 micrograms per serving.
- Limit selenium in supplements to 100 micrograms per day.
- Limit Vitamin A in supplements to 100% of daily value (5000 IU). Or, even better, take a supplement that contains beta-carotene rather than Vitamin A.