Clinical data increasingly has shown that patients with low vitamin D levels have a greater chance of COVID-19 infection—and severe disease and death. Now, research points to an explanation for the link and provides evidence that higher vitamin D intake can help fight off the disease. The study indicates the vitamin strengthens the lung lining and possibly also reducing fluid leakage into the airways, which causes pneumonia. "Your body is mostly sacs and tubes," said James Mullin, Ph.D. "If their linings are in good shape, you're in good shape. If they're leaking and fail to provide a proper barrier, it's...