Vitamin D reentered the public consciousness as an immune system booster in late 2009 after several studies from around the globe showed that the health-enhancing compound could be used to protect against swine flu and other infectious disease. Moreover, vitamins D2 and D3 have been proven to hold a number of other great benefits, from preventing cancer and cardiovascular disease to improving mental health. Get your levels checked and make sure you get enough by eating yogurt, fortified cereals or juice, milk and fatty fish like salmon — or simply escape to a sunnier climate!