ROCHESTER, Minn. — Over the past few years, studies have found that vitamins previously considered beneficial may not be helping — and may be causing harm. The March issue of Mayo Clinic Health Letter provides an overview on the latest advice about taking vitamins.
The newest research is from the Iowa Women's Health Study. This 20-year study of 38,000 women age 55 and older showed that taking a multivitamin appears to increase the risk of premature death. Evidence from this study and others suggest there is no need to take most supplements for general health or disease prevention. Exceptions appear to be calcium supplements and vitamin D for bone health.
The Mayo Clinic Health Letter highlights some potentially risky supplements:
Vitamin E: A 2005 review of research found that taking daily vitamin E supplements of 400 international units (IU) or more and possibly as low as 150 IU a day may pose health risks, including increased risk of premature death.
Vitamin A: A large study of postmenopausal women found that long-term intake of at least 6,660 IU of vitamin A acetate or palmitate may increase the risk of hip fractures. However, other research hasn't come to the same conclusion.
Folate and folic acid (vitamin B-9): Supplementation helps prevent birth defects, but evidence of other benefits has been elusive. The Iowa Women's Health Study suggests that folic acid supplements might increase the risk of premature death by 5.9 percent. Other studies have linked folic acid supplements with an increased risk of colorectal cancer.
Vitamin B-6: Large daily doses — more than 100 milligrams (mg) — can cause nerve damage over time. In the Iowa study, vitamin B-6 appeared to increase the risk of premature death by 4.1 percent.
Vitamin B-3 (niacin): High doses can help lower high cholesterol levels. This treatment should be done under a doctor's supervision because side effects can include severe liver disease.
Trace minerals: Copper, chromium, magnesium, selenium and zinc are among the essential trace minerals. There is no solid evidence that trace mineral supplements have any benefit in the absence of deficiencies — which are rare. The Iowa Women's Health Study indicated that the risk of premature death increased 3.6 percent in those taking magnesium, 3 percent in those taking zinc, and 18 percent in those taking copper supplements.
It's always wise to consult with a doctor about any diet supplements. There are situations where supplements are beneficial to health. But healthy individuals who take supplements as an "insurance policy" against inadequate nutrition may in fact be increasing their health risks.
Mayo Clinic Health Letter is an eight-page monthly newsletter of reliable, accurate and practical information on today's health and medical news. To subscribe, please call 800-333-9037 (toll-free), extension 9771, or visit Mayo Clinic Health Letter Online.
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