WASHINGTON – Don’t be surprised if your doctor orders a vitamin D test during your next physical.

Blood tests to check levels of the so-called sunshine vitamin are on the rise as doctors and patients react to headline-grabbing research that suggests having too little not only may hurt your bones – it also might increase your risk of certain cancers or heart disease.

But there are problems with deciding next steps: As intriguing as the research is, it’s far from proof that vitamin D really is that powerful. Also, it’s not clear just how much is enough – and megadoses can harm.

Nor are there guidelines on exactly who should be tested, or how. Test during winter, for example, and in much of the country people will harbor considerably less vitamin D than if they were tested in the sunny summer.

Still, “the hope is so high that it will have some effect that everybody’s asking for it,” says Dr. Clifford Rosen of the Maine Medical Center, who is helping government researchers evaluate the research. “It’s pretty much the wild, Wild West right now.”

There is no count of how many people get their vitamin D checked. But at testing giant LabCorp, the volume of vitamin D tests doctors order has, on average, doubled every year for the past four, says spokesman Eric Lindblom. So far this year, test orders are up another 90 percent. At competitor Quest Diagnostics, the volume of D tests approximately tripled between May 2006 and last May.

Dr. James Underberg, a New York University internist, once checked vitamin D levels mostly in people at risk of thinning bones. Over the past year, he has begun screening more patients, especially those at risk of heart disease, as he closely watches the evolving research.

“We don’t have any data yet that says taking an otherwise healthy adult who’s vitamin D deficient and supplementing them prevents cancer, reduces the risk of heart disease,” Underberg acknowledges.

“You just have to keep your eyes and ears open to make sure something doesn’t show up counterintuitive to what people thought,” he adds, noting that other once-touted heart protections – estrogen therapy after menopause, for example – failed when more rigorously researched.

Dr. Ann Marie Gordon, a Washington, D.C., internist, isn’t hesitating. She has made a vitamin D test a routine part of every physical, and she estimates that 60 percent of her patients are low.

“Any kind of deficiency needs to be addressed. Whether patients are convinced or the medical world is convinced that vitamin D goes beyond bones is irrelevant,” she says.