It's a well-known fact that older women need calcium and vitamin D to fight bone loss. But it's also important that younger, active women get calcium and vitamin D to prevent stress fractures.

A recent study looked at more than 5,000 female U.S. Navy recruits and found that those who didn't take additional calcium and vitamin D were 25% more likely to suffer a stress fracture.

The authors of the study recommend that women take calcium and vitamin D supplements before starting any new exercise regime. But you can also opt to get your calcium and vitamin D naturally. Dairy products such as low-fat milk, yogurt, and cheese are good sources of calcium, but there are other nutrition sources as well. Your best source of vitamin D is the sun; fish and vitamin D fortified foods (milk, orange juice, and cereals are often fortified with vitamin D) are also sources.