Dr. Arefa Cassoobhoy: Study after study has linked low vitamin D levels with various diseases, such as MS, Alzheimer’s, diabetes, heart disease and cancer, to name a few. This has led to assume that taking extra vitamin D could actually help treat some of these illnesses. But the jury is still out. We don’t know if it will help. It’s a chicken and egg kind of thing: Does being sick lead to low vitamin D or does a low vitamin D level trigger other medical problems? OR, is something else completely different going on? While we wait for researchers to answer those questions, we do know this. Vitamin D is critical for strong, healthy bones throughout your life. Getting enough from the sun can be a challenge when you’re wearing sunscreen to protect your skin. And very few foods have vitamin D besides fortified milk, so it can be tough to rely on your diet to get vitamin D. For many people, a vitamin D supplement is a good idea. Check with your doctor to see how much you need to protect your bones. And for now, we’ll wait to see if taking vitamin D can help treat any other illnesses. For WebMD, I’m Dr. Arefa Cassoobhoy.