Sardines are small fish which are often packed with oil or tomato sauce into small flat cans. Like most fish, they are excellent sources of omega-3 fatty acids, which lowers cholesterol level and thus your risk of heart disease, and keeps your immune system, as well as your skin and hair, in good shape. Because of the soft bones, one tin of sardines has more calcium than a glass of milk. In addition, fish are one of the few natural sources of vitamin D. Together, calcium and vitamin D help keep your bones strong and osteoporosis-free. And sardines contain iron. All in all, a good source of some necessary nutrients.