Next time you’re at the doctor’s office, request a simple blood test to evaluate your vitamin D blood levels, suggests Doreen Orion, MD, a physician in private practice in Boulder, Colorado, and the author of the memoir Queen of the Road. “We're finding that many, many women have a low level of this essential vitamin,” she says. “Low levels are correlated with all sorts of things from cancers to low energy to Alzheimer's. I've had patients who are outside all day, who still have very low levels. The fix is simple and just involves taking vitamin D for several months, then rechecking the level.”