Vitamin D, known as the sunshine vitamin, is important for strong bones. You can get it from sun exposure and foods, such as milk, cereals and fortified yogurt.

Deficiency can occur when your skin's ability to make vitamin D decreases with age, or when you have conditions that reduce the body's ability to absorb it. Severe deficiency can cause rickets in children and osteomalacia in adults.

Deficiency Effects

The most severe vitamin D deficiency causes the bones to become soft and misshapen (rickets). Children may have a curved spine (scoliosis) or knock-knees. They are slow to walk and often complain of bone pains. The condition is easily diagnosed with blood tests to measure vitamin D levels and x-rays to look for characteristic changes in the bones. The blood tests can also check levels of calcium and phosphate. A high parathyroid hormone level indicates hyperparathyroidism, which is sometimes a complication of vitamin D insufficiency.

Deficiency is common in people of all races and ages, but prevalence increases with age. It is lower in whites and higher in blacks than in other groups. Rates of deficiency are lower among adolescent boys than adolescent girls.

The Food and Nutrition Board committee that established vitamin D intakes concluded that it is unlikely that low serum 25(OH)D concentrations have a relationship to health outcomes other than bone health, but the data are limited and inconclusive. The body makes most of the vitamin D it needs, but some medical conditions (such as Crohn's disease or coeliac disease) or certain medicines (including carbamazepine, phenytoin, primidone and some anti-HIV drugs) can affect the way it is made or absorbed. In addition, skin pigmentation can affect the ability to make vitamin D in the skin.

Health Risks

Many people with vitamin D deficiency don’t have symptoms and it can be hard to diagnose. Children with severe deficiency have soft skull and leg bones (rickets). They may also be short in stature, have teething problems or have a curved appearance to the legs (bow-legged).

A person’s skin can make vitamin D when exposed to sunlight. But the ability to make vitamin D decreases with age and it’s more difficult for people with darker skin to make enough from the sun.

Other factors that increase the risk of vitamin D deficiency include a lack of exposure to sunlight due to living in a northern climate, having a skin condition that limits the production of melanin (e.g., psoriasis or vitiligo), having a medical condition that interferes with the absorption of vitamin D (e.g., Crohn’s disease, celiac disease or having had gastric bypass surgery), being overweight and having a disease that causes inflammation, such as inflammatory bowel syndrome.

Vitamin D is found in foods, mainly oily fish (sardines, pilchards, herring, trout, salmon, mackerel and tuna), liver and egg yolks. Some foods are fortified with vitamin D, including some milk and margarines. It is also available as a supplement. Taking high doses of vitamin D usually corrects the deficiency and symptoms within about a month.

Prevention Tips

The best way to prevent vitamin D deficiency is by getting enough sun and eating a nutritious diet. Known as the sunshine vitamin, vitamin D helps your body absorb calcium and build strong bones. It's also found in certain foods, such as fish (especially salmon and trout), egg yolks, fortified dairy products and orange juice.

However, if you have certain medical conditions, it may be hard to get the vitamin D you need through your diet or sunlight. Fat malabsorption -- common in people with cystic fibrosis, Crohn's disease, ulcerative colitis and celiac disease -- can make it difficult for your gut to absorb fat-soluble vitamins, including vitamin D.

In some cases, your doctor may recommend a vitamin D supplement of 400 to 800 IU per day. You can find these over-the-counter in the form of cholecalciferol or ergocalciferol. If you have a severe deficiency, your doctor can prescribe vitamin D in much higher doses and may also recommend magnesium to help your body activate the vitamin. Vitamin D injections are also available if needed.