Brittle bones. Colon cancer. Migraines. Heart disease.

Vitamin D has been linked to all of these, touted as a potential wonder drug for its curative and preventive powers. Doctors in Maine frequently prescribe the supplement because of our weak sunlight and older population.

But does it work?

Cliff Rosen, M.D., has spent the better part of the last decade trying to find answers. The director of the Center for Clinical & Translational Research at Maine Medical Center’s research facility in Scarborough, Rosen is working with the National Institutes of Health to examine effects of vitamin D on bone and fat tissues. His work has lent an authoritative voice to the debate about what consumers can expect from one of the most-prescribed vitamin supplements in the U.S.

“The problem is the evidence is very minimal,” said Rosen, who counted 39 diseases that low vitamin D is associated with. “But these are non-causal associations. The only way we can prove causality is by doing clinical trials.”

He’s recruiting people now to participate in a three-year clinical trial he’s conducting with Tufts Medical Center to test the efficacy of vitamin D to prevent diabetes. According to a Maine Center for Disease Control and Prevention study, about 11.4 percent of Mainers have diabetes.

“These are the kinds of studies that have to be done,” Rosen said.

He notes that vitamin D is not a true vitamin, a term reserved for organic compounds that can’t be produced by the body. Humans can produce vitamin D – all it takes is uninterrupted sun exposure.

But whether a person can get adequate amounts from sun exposure and from their diets has pushed great interest in vitamin D supplements. Richard Maurer, N.D., a Portland naturopath, which is a class of medical provider that treats patients holistically, said blood tests to measure vitamin D levels are now the third-most ordered blood test in the country.

“I order one for everyone I see to get a baseline,” said Maurer. “Of the last 100 people I’ve seen, over 50 percent are below the reference frame for healthy vitamin D levels.”

The vitamin is essential for good health. The National Institutes of Health recommends adults from 18-70 should get 600-800 IU (international units) of vitamin D a day. Without adequate vitamin D, the human body can’t absorb enough calcium to build a strong skeleton. The vitamin acts as a bodyguard, escorting calcium safely to bones and teeth. In children, a vitamin D deficiency can lead to rickets, which is why most milk is fortified with it. But in adults, deficiencies can lead to osteoporosis, making a person more susceptible to bone fractures.

Rosen’s research to date has verified one claim about vitamin D – it has a modest effect on the treatment of osteoporosis and osteopenia, the gradual decline of bone strength, a condition especially common in post-menopausal women.

Maine is the nation’s oldest state with an average age of 43.5, and 18.3 percent of its population is 65 or older, compared with the national average of 14.5 percent. It also has weaker sunlight, courtesy of its northern location and frequent cloud cover.

For that reason, Rosen said it’s prudent for post-menopausal women to take supplements of 800 to 1,000 IU per day in the winter and 600 to 800 IU per day in the warmer months.

Aside from post-menopausal women, Rosen doesn’t see a need to prescribe vitamin D as a supplement although he acknowledges it is widely done. The reason, he suspects, has to do with how easy it is to measure vitamin D levels via a simple blood test, and to raise those levels by popping a capsule every day. That kind of engagement with a patient can prod them to be more aware and take greater responsibility in managing their own health care.

Maurer takes a more measured approach to vitamin D, saying most people in Maine would benefit from taking a supplement, although not at a very high level.

“A few years ago, there was all this hype revolving around vitamin D, like it could be used to treat diabetes, autoimmune disorders, migraines and the like,” he said. “Prescribing for vitamin D became overzealous.”

He recommends adults take 1,000 IU of vitamin D daily. Maurer cautions, though, that no one should take more than 2,000 units without medical supervision.

“If you go above 2,000, there’s a chance there’ll be too much calcium formed in your body,” he said. “For someone with arthritis, that could make the problem worse.”