The body needs vitamin D to help absorb calcium, which is responsible for keeping bones, muscles and even the heart healthy and strong. Without enough vitamin D, men and women are at a heightened risk for osteoporosis, a bone condition in which bones become brittle and fragile due to tissue loss. Vitamin D is also beneficial for those who love to exercise. Muscles that don't get enough calcium will cramp, hurt or feel weak, possibly leading to chronic muscle aches pains. If the body is getting enough vitamin D, muscles are less likely to cramp or ache. While it's possible to include vitamin D in a daily diet, it's also difficult because there are not many foods rich in vitamin D. However, men and women can take a multivitamin or even a vitamin D pill to ensure they get their daily recommended amount of vitamin D.