Consumer Reports Insights

Vitamin and mineral supplements haven't proved effective in preventing disease

(Larry Jost)
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Tuesday, March 16, 2010

Americans want to believe in vitamin and mineral pills. We spent an estimated $10 billion on them in 2008, according to the Nutrition Business Journal.

But recent studies undertaken to assess their benefits have delivered a flurry of disappointing results. The supplements failed to prevent Alzheimer's disease, cancer, heart attacks, strokes, Type 2 diabetes and premature death.

While some people may need supplements at certain stages of their lives, nutritional deficiencies are uncommon in the United States. Major health organizations for cancer, diabetes and heart disease all advise against supplements in favor of a healthful diet rich in fruits, vegetables, whole grains and legumes. Unlike pills, those foods contain fiber plus thousands of health-protective substances that seem to work together more powerfully than any single ingredient can work alone.

Another concern is that some vitamin pills can be toxic if taken in high doses for a long time. Studies show that beta carotene pills, for example, can increase the risk of lung cancer in smokers, and a 2008 review suggests that the pills, plus supplemental doses of the vitamins A and E, may increase the risk of premature death. Yet despite such unfavorable results, vitamin and mineral pills are widely used to fend off diseases.

There is insufficient evidence to support the use of supplements to prevent the following conditions:

-- Cancer. Two large trials published in 2009 came up empty. In one, sponsored by the National Cancer Institute, researchers reported that Vitamin E and the mineral selenium failed to prevent prostate cancer. In fact, researchers noted possible increased risks of prostate cancer from Vitamin E and of Type 2 diabetes from selenium. The second study, the Physicians' Health Study II, found that neither Vitamin C nor E reduced the risk of colon, lung, prostate or other cancers in men.

-- Heart disease. Folic acid and other B vitamins failed to prevent heart attacks, strokes and death from cardiovascular disease in women at risk for heart disease in a 2008 trial by the Harvard Medical School. And neither Vitamin C nor E prevented those events in men in the Physicians' Health Study II. Vitamin E, however, was linked to an increased risk of hemorrhagic stroke. Antioxidant supplements were previously thought to prevent fatty buildups in arteries, but research now suggests that they may worsen cholesterol levels and blunt the effects of cholesterol-lowering drugs.

-- Type 2 diabetes. In a 2009 trial, vitamin and mineral pills didn't reduce the risk of metabolic syndrome -- a cluster of symptoms including abdominal obesity and high levels of LDL (bad) cholesterol and blood sugar -- which can lead to Type 2 diabetes. Additional 2009 studies found that vitamin pills didn't prevent Type 2 diabetes and might undermine the ability of exercise to improve blood sugar levels.

-- Cognitive decline. B vitamins didn't slow Alzheimer's disease, and Vitamin E failed to prevent dementia in people with cognitive impairment, according to trials from the Alzheimer's Disease Cooperative Study, funded by the National Institutes of Health. On the other hand, a deficiency of Vitamin B12 or thyroid hormone can cause cognitive impairment, so if you're declining more than normal for your age, you should be tested for those conditions.

-- Immune function. The evidence on whether vitamin and mineral supplements can enhance immunity is contradictory, especially for people who eat adequately. And while supplements can boost immune response in older people with nutritional deficiencies, it's still not known if that results in fewer infections.

Some evidence supports the use of supplements for these conditions:

-- Eye disease. People who have at least moderate age-related macular degeneration (AMD), a leading cause of blindness, may be able to limit further damage by taking a daily supplement that contains vitamins C, E and beta carotene.

-- Osteoporosis. In a recent comprehensive review of 167 studies, the federal Agency for Healthcare Research and Quality found that calcium and Vitamin D pills reduced fractures and bone loss, although the fracture benefit was primarily only in female nursing-home residents.

Copyright 2010. Consumers Union of United States Inc.

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