Harvard Health Letter

Vitamins: Benefit of the doubt vs. doubts about benefit

Negative studies have piled up, but are they a fair test?

Good news about vitamins is hard to find these days. Headline after headline — including a few in this newsletter — blare negative results. B vitamins don't prevent heart attacks. Vitamin E doesn't benefit people with Alzheimer's disease. Vitamins A, C, and E — no cancer protection there.

Lack of benefit is one thing. But mixed in with the null findings are a few that suggest large doses of vitamins might cause some real harm. One of the first came in 1994, when results from a high-profile Finnish study linked beta carotene, a form of vitamin A, to an increased risk of lung cancer in male smokers. Several years later, high intake of retinol — another form of vitamin A — was linked to hip fractures.

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