Think you should avoid the sun at all costs this summer? Not so fast, say University of Colorado researchers, who noticed a big jump in vitamin D deficiency after reviewing nearly 20 years of data from more than 32,000 people. Lack of the vitamin—the best source of which is sunshine—has been linked to higher risk for cardiovascular disease, cancer and osteoporosis. Of course, too much sun can also be dangerous. What to do? Researchers recommend getting 10 minutes (but no more) of sunlight on exposed arms or legs two or three times per week, or adding vitamin D-fortified foods to your diet. Two 8-ounce glasses of fortified milk or OJ per day can do the trick.