Researchers at the University of California at San Francisco found that more than half the HIV-positive people they tested had low levels of vitamin D—and that the lack contributed to a higher risk of heart disease. You have heard similar news before, so if you haven't yet asked your doctor to check your D levels (it's a simple blood test), you might want to do that now. Although the researchers emphasize that it is not yet known whether vitamin D supplementation will help your heart, keeping your D up provides enough other important health benefits to merit a swallow. Got milk?