You're overbooked and overworked. Between your job, your family, your fitness routine and all the to-dos on your list, it's no wonder you're tired sometimes (or, um, all the time). But if you feel as if you're running on empty most days and find that getting more sleep hasn't helped, you may have an underlying health problem, says Molly Cooke, MD, the president of the American College of Physicians. Here, six surprising conditions that can leave you drained.
Related: The All-Day Energy Guide
You need more vitamin D.
Up to 40 percent of us are deficient in D, the vitamin that protects against osteoporosis and several autoimmune diseases and may also help fight cancer and high blood pressure. "You have vitamin D receptors in your muscles and in almost every organ of your body, including your heart and brain," explains Sue Penckofer, PhD, a professor at the School of Nursing at Loyola University in Chicago. If you're low in it, you may have no energy.