You know your height and weight. You probably have a rough idea about your cholesterol number and what it should be. You might know your blood pressure. But there’s another number that most people don’t know, but should.

That number is your 25 hydroxy vitamin D level. Modern Americans avoid sun exposure in an effort to avoid wrinkles and skin cancer. But skipping the sunshine means that they don’t make enough vitamin D. Many studies have now established that the lower your vitamin D, the higher your risk of cancer, autoimmune disease, and premature death.

I recommend that everyone get their vitamin D checked each spring and fall. If you haven’t had your vitamin D level checked recently, have your doctor do this test. A vitamin D level below the 25th percentile doubles your risk of death as compared to being at the 50th percentile. Go ahead and avoid the sun, but take your vitamin D. Check out in our Longevity Store.