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Study: Low vitamin D is result, not cause, of disease

LONDON -- Vitamin D supplements don't help prevent chronic diseases unrelated to the bones, according to a review of research that challenges the prevailing wisdom held by proponents.

While scientific evidence supports the importance of vitamin D for bone health, its benefits in reducing the risk of diseases ranging from cancer to heart disease as shown in 290 observational studies were largely unconfirmed in 172 randomized controlled trials, experiments considered the gold standard for establishing causal links, according to the review published yesterday in The Lancet Diabetes & Endocrinology medical journal.

The discrepancy in findings between the two types of studies suggests that low levels of vitamin D aren't a cause but a consequence of ill health, particularly inflammation linked to many diseases, according to the review's lead author, Philippe Autier, a professor at the International Prevention Research Institute in Lyon, France. The research has implications for almost half of all U.S. adults, who are paying $600 million a year for vitamin D pills.

In randomized controlled trials, scientists assign a treatment or placebo to study participants who don't know which one they're getting to tease out whether the treatment is causing the outcome. In observational studies, there are no such comparison groups.

The randomized trials on vitamin D showed little to no effect in lowering risk for heart disease, diabetes, infectious diseases and mood disorders, among other conditions. In contrast, the observational studies generally reported moderate to strong effects on these disorders.

The U.S. National Institutes of Health recommends 15 micrograms of daily vitamin D intake from ages 1 through 70. People older than 70 should consume 20 micrograms.

-- Bloomberg News