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The popularity of vitamin D has been surging in recent years, largely because of the growing list of its proposed health benefits. But not all of the claims are backed by evidence. For example, there have been suggestions that vitamin D can help you

• reduce your risk of arthritis
• prevent heart disease
• improve your brain function and lessen your risk of dementia
• improve your immune function and lessen the risk of immune disorders.

These are difficult claims to prove 鈥� or disprove. Most of them come from studies linking a low intake of vitamin D or a low level in the blood with an increased risk of disease or death. But, it鈥檚 possible that people with low intake or blood levels of vitamin D levels also smoke more, exercise less, or have other explanations for their higher rates of disease and death.

While it鈥檚 not at all clear that vitamin D can deliver these health benefits, getting enough vitamin D is important, especially for maintaining bone health. Severe deficiency of vitamin D can cause osteomalacia, which means 鈥渟oft bones.鈥� (In children, abnormal bone development due to vitamin D deficiency is called rickets.) Low levels of vitamin D can also contribute to osteoporosis: vitamin D is needed to promote calcium absorption in the gut, and calcium is essential in building and remodeling bone.

Can vitamin D also improve physical function?

To explore the possibility that vitamin D might provide yet another health benefit, researchers to determine whether taking a high dose vitamin D supplement might help stave off a decline in physical function in older adults. Researchers enrolled 200 people who were at least age 70 and who had reported a fall in the past. Some were given a low dose of vitamin D, while others received higher doses. After a year, the researchers assessed the participants鈥� physical function (by measures of walking speed, ability to stand up repeatedly from a sitting position, and balance). The results were no better in those treated with higher doses of vitamin D than in those on lower doses. In addition, those receiving the higher doses reported significantly more falls. There was no clear explanation for this unexpected finding.

While this study casts doubt on vitamin D as a panacea for failing physical function among elderly adults, it鈥檚 still possible that it might help certain people 鈥� for example, perhaps younger adults who鈥檝e never fallen before would see more benefit. Or, a longer period of follow-up might reveal other benefits associated with taking high-dose vitamin D supplements.

Please stand by

While we know vitamin D is an essential part of a healthy diet and supplements might be helpful for those who don鈥檛 get enough, we need more research to back up some of its proposed benefits. In the meantime, it seems reasonable to choose a balanced diet that contains the for your age and gender. Sun exposure (perhaps as little as 10-15 minutes a day) may also increase blood levels of vitamin D because UVB radiation from the sun converts precursors of vitamin D in the skin.

Talk to your doctor about whether to have a blood test to confirm that you鈥檙e getting enough vitamin D. And read the reports about the health benefits of this vitamin (and other vitamins and supplements) with a skeptical eye. There is considerable uncertainty about what vitamin D can do for you 鈥� and, as demonstrated in this latest research, one thing is clear: more is not always better.