Vitamin D helps your body absorb calcium, which is needed to build and maintain strong bones. People with low vitamin D levels may have low bone mass or low bone density.

Vitamin D helps protect your bones. Calcium works with vitamin D to build bone mass in children and keep bones strong and healthy in adults. Maintaining appropriate levels of vitamin D and calcium is especially important for women, because they are more likely to develop osteoporosis (a condition that makes bones weak and easily breakable).

You can get vitamin D from 3 sources:

• Sunlight

• Food

• Supplements and medications.

Your skin makes vitamin D from the sun’s rays. This is why vitamin D is known as the "sunshine vitamin." The amount of vitamin D your skin makes depends on the time of day, season, your location (southern and southwestern regions of the United States are generally sunnier), skin color, and age. However, it may be best to stay out of the sun because of concerns of skin cancer. Sunscreens block the rays necessary for your skin to make vitamin D, and being in the sun without sunscreen can make you vulnerable to the sun’s harmful effects. Many people thus obtain vitamin D from other sources, such as food or supplements.

Foods rich in vitamin D include fatty fish (like mackerel, salmon, and tuna), egg yolks, and beef liver. Vitamin D is sometimes added to many other foods, such as milk, margarine, and breakfast cereals. It is very difficult to get all the vitamin D you need from food alone. This is why people may also take vitamin D supplements. Before taking any supplement, talk to your health care professional. Find out if your calcium supplement, multivitamin, or medication already contains the right amount of vitamin D for your needs. If so, you may not need a separate vitamin D supplement.

• Salmon (3.5 oz): 360 IU

• Mackerel (3.5 oz): 345 IU

• Tuna, canned (3.5 oz): 200 IU

• Beef liver (3.5 oz): 15 IU

• Egg (1, whole): 20 IU

• Margarine (fortified, 1 tbsp): 60 IU

• Milk (fortified, 8 oz): 98 IU

• Breakfast cereals (fortified, 1 cup): 40 IU

Some people may not be getting enough vitamin D. You may be at risk if you:

• spend little time in the sun

• have very dark skin

• are age 50 or older

• have certain medical conditions like pancreatic enzyme deficiency, Crohn’s disease, cystic fibrosis, celiac disease, or some forms of liver disease

• are obese.

A blood test can determine if you are getting enough vitamin D. If you feel you may be at risk for vitamin D deficiency, be sure to talk to your health care professional about this test and options for increasing your vitamin D intake. Remember: vitamin D is crucial in helping protect your bones. It works with calcium to strengthen your bones and decrease your chance of developing osteoporosis. Vitamin D is especially important for women, because they are more likely than men to have low bone mass or low bone density.