Healthy bones depend on calcium, which in turn depends on vitamin D for absorption into the body. Vitamin D is just as important in building and maintaining healthy muscles.

Vitamin D helps muscle cells mature and function and keeps them active and strong enough to support your body. On the other hand, lack of vitamin D can make your muscles weak.

Unfortunately many older adults don't consume enough vitamin D to meet their daily needs. The recommended intake for vitamin D for those over the age of 70 is 600 milligrams. One cup of milk contains about 100 milligrams of vitamin D.

The best food sources of vitamin D are fortified milk, fatty fish and fortified cereals.