WASHINGTON (AP) -- 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 may not only hurt your  bones -- it 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