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Vitamin D doesn't prevent disease for most, study says

11/23/2016, 10:01 p.m.
Vitamin D supplements do not help prevent disease for the majority of people, according to a new study published Wednesday ...
A growing number of older adults are combining multiple prescription and over-the-counter medications and supplements in ways that could lead to serious side effects, according to a new study. (Mark Hill/CNN)

— Vitamin D supplements do not help prevent disease for the majority of people, according to a new study published Wednesday in the British Medical Journal.

During the bleak winter months of short days and cloudy skies, many people may seek out the benefits of sunshine in bottle form and reach for supplements of vitamin D. Made naturally by the skin when exposed to sunlight, this vitamin is needed to maintain healthy bones, teeth and muscles and to prevent them from becoming brittle and at risk of fracture.

But a review of evidence from clinical trials on the impact of supplements has found that attempting to get vitamin D through supplements is not so beneficial.

"We conclude that current evidence does not support the use of vitamin D supplementation to prevent disease," said Mark Bolland, associate professor of medicine at the University of Auckland, New Zealand, in a statement. Bolland led the research with Alison Avenell, a clinical chair in health sciences research at the University of Aberdeen.

According to the team, clinical trials have failed to show that supplementation reduces the risk posed by falls and fractures to bones and muscles. But they recognize that it may be beneficial in people who are at high risk, such as those in nursing homes and darker-skinned people living in colder climates.

To those at risk, researchers do recommend supplements during autumn and winter but also suggest getting advice on how best to get vitamin D naturally. "Vitamin D will protect people who are at high risk," Avenell said.

Natural sources

In spring and summer in the far regions of the Northern and Southern Hemispheres, such as the northern US and New Zealand, people tend to produce enough vitamin D through sunlight on their skin and foods in their diet. The vitamin helps the body absorb calcium to promote bone growth.

Getting enough vitamin D, calculated as 15 micrograms for ages 1 through 70 in the United States, also prevents rickets in children and osteomalacia -- bone softening -- in adults. "We're taking about preventing these diseases," said Avenell.

But during autumn and winter, levels drop. It helps to eat the right foods, such as oily fish, egg yolks, red meat and liver, to keep levels high inside the body -- which not everyone can achieve adequately. Fortified foods, including milk, cereals and spreads, provide the most vitamin D in the American diet, according to the National Institutes of Health.

"In the US, vitamin D supplementation (through food) is higher," Avenell said.

In countries like the UK, however, foods are not fortified as often, and supplements are therefore recommended. Until recently, recommendations were mainly to people at high risk of rickets and osteomalacia, but this summer, Public Health England advised that everyone take the equivalent of 10 micrograms per day.

"That's a big change," Avenell said. "We don't think the evidence supports the necessity for that during winter."

In a separate article, also published Wednesday, Dr. Louis Levy, head of nutrition science at Public Health England, argued that the recommended dose is backed by the Scientific Advisory Committee on Nutrition, which also reviewed the evidence.