Vitamin D helps your body absorb calcium from the foods you eat, and also plays a role in balancing calcium and phosphate levels in your blood. Because of this relationship with calcium, it's essential for healthy bones.
Vitamin D is also necessary for keeping your nervous system, muscles, and immune system functioning properly, and for normal cell differentiation and growth.
Vitamin D deficiency can result in weak, brittle bones. Children who don't get enough may have rickets, and adults with vitamin D deficiency are at a greater risk for osteoporosis.
The adequate daily intake for vitamin D is from 200 to 600 International Units (IU); however, some experts believe those numbers should be increased. Three ounces of salmon contains about 800 IU, a cup of milk has just over 100 IU, and one serving of fortified breakfast cereal usually has about 40 IU vitamin D.
Symptoms of Deficiency
People with vitamin D deficiency may experience bone pain and muscle weakness, although the symptoms may be very mild at first.
Children who have rickets suffer from soft bones and skeletal deformities. Deficiency in adults will cause osteomalacia, or weakened bones. Your health care provider can order tests that measure the levels of 25-hydroxy vitamin D.
Insufficient levels of vitamin D in the blood have been associated with a variety of other health conditions such as diabetes, hypertension, multiple sclerosis and some forms of cancer. However, more research is needed to determine if vitamin D can actually prevent or treat any of these disorders.
Not eating foods that contain vitamin D and not getting enough sun exposure may lead to vitamin D deficiency. Breastfed infants, older adults, housebound individuals and people with dark skin are at higher risk of vitamin D deficiency.
People who have fat absorption problems due to conditions such as Crohn's disease, cystic fibrosis, gastric bypass surgery or have liver or kidney conditions may not get enough vitamin D from their diets.
You need sun exposure to make vitamin D, but it only takes 5 to 30 minutes of sun exposure on your face, arms, legs or back twice each week without sunscreen to stimulate sufficient vitamin D production. Excessive sun exposure increases your risk of skin cancer, so it's important to use sunscreen and limit your use of tanning beds.
Vitamin D is not naturally present in many foods; however, oily fish and especially cod liver oil are rich in vitamin D. Beef liver, eggs and cheese also contain small amounts. Vitamin D is added to some foods like milk and fortified breakfast cereals.
Can You Get Too Much?
Your body stores fat-soluble vitamins such as vitamin D, but excessive sun exposure will not cause vitamin D toxicity. It would be extremely difficult to get too much vitamin D from foods -- even fortified foods -- unless you consume large amounts of cod liver oil.
You can take vitamin D supplements - usually as vitamin D2 or vitamin D3. Taking large doses of these supplements can lead to vitamin D toxicity that causes nausea, vomiting, loss of appetite, constipation, weakness and weight loss.
High levels of vitamin D in your body can also raise your blood levels of calcium, which can result in mental confusion and an abnormal heart rhythm. If you want to take vitamin D supplements, follow the label directions unless your health care provider tells you differently.
Office of Dietary Supplements National Institutes of Health. "Dietary Supplement Fact Sheet: Vitamin D." Accessed September 17, 2010. http://ods.od.nih.gov/factsheets/vitamind/