Your body needs vitamin D to absorb calcium properly. Vitamin D is produced naturally by your body when your skin is exposed to sunlight and can also be obtained from some foods, eg oily fish. However, most people don't get enough from these sources. Because of this, your doctor will probably prescribe vitamin D supplements to treat your osteoporosis. Taking 35-50 micrograms of vitamin D a day (about 3-4 high-strength, 12.5-microgram tablets) is also thought to reduce your risk of developing various cancers.
Attribution: BUPA