The Medical Letter is a biweekly publication which publishes the most unbiased reviews of medications. It is not supported by advertising and prides itself in giving objective evidence-based information. I think it’s mandatory reading for anyone with a prescription pad. Several of my posts have been inspired by Medical Letter articles, and this week they’ve come through again with a review of vitamins titled “Who Should Take Vitamin Supplements?” The article reviews in detail the clinical trials which have tested the effects of the most commonly taken vitamins. I summarize these below.
Vitamin E supplements have been shown to increase the risk of prostate cancer, not to decrease the risk of stroke or heart attack, and not to decrease the risk of eclampsia in pregnancy.
Beta-carotene is a precursor of vitamin A. A randomized trial in smokers found that a high dose beta-carotene supplement significantly increased the risk of lung cancer. Another randomized study in asbestos workers showed that supplementation with vitamin A and beta-carotene led to higher lung cancer rates than placebo.
Vitamin D is essential in older people in preventing fractures and falls. Many people with limited sun exposure are deficient in vitamin D.
Vitamin C has been shown not to prevent the incidence of cancer, strokes, or heart attacks. It does not significantly decrease the risk of developing a cold or significantly improve cold symptoms. High doses can predispose to kidney stones.
Vitamin B12 deficiency is common in older patients and can lead to anemia and nerve dysfunction.
Folate should be taken by all child-bearing-age women to prevent neural tube defects in their babies. Folate supplementation has no known benefits in men.
Vitamin B6 supplementation has been proven not to decrease the incidence of strokes, heart attacks, or any cancer.
The authors conclude:
“In healthy people living in developed countries and eating a normal diet, the benefit of taking vitamin supplements is well established only to ensure an adequate intake of folic acid in young women and of vitamins D and B12 in the elderly. There is no good reason to take vitamins A, C or E routinely. No one should take high-dose beta-carotene supplements. Long-term consumption of any biologically active substance should not be assumed to be free from risk.”
That last sentence deserves our attention. Many people assume that even if vitamins aren’t helpful, they are at least harmless. The Medical Letter reminds us that this assumption should be tested, and when tested is sometimes proven false.
More Than Half of Americans Take Dietary Supplements (My post in April on multivitamins)
All my previous posts on various vitamins
Who Should Take Vitamin Supplements? (The Medical Letter article, issue 1379, only by subscription)
Important legal mumbo jumbo:
Anything you read on the web should be used to supplement, not replace, your doctor’s advice. Anything that I write is no exception. I’m a doctor, but I’m not your doctor.