Vitamin D deficiency

If you shun the sun, suffer from milk allergies, or adhere to a strict vegetariandiet, you may be at risk of vitamin D deficiency. Known as the sunshine vitamin, vitamin D is produced by the body in response to sunlight. It also occurs naturally in a few foods -- including fish, fish liver oils and egg yolks -- and in fortified dairy and grain products.

Vitamin D is essential for strong bones because it helps the body absorb calcium from the diet. Traditionally, vitamin D deficiency has been associated with rickets, a disease in which the bone tissue doesn't properly mineralise, leading to soft bones and skeletal deformities. Research is revealing the importance of vitamin D in protecting against a host of health problems.

Symptoms and health risks of vitamin D deficiency

Symptoms of bone pain and muscle weakness can mean you have a vitamin D deficiency, although for many people, the symptoms are subtle. Even if there are no symptoms, too little vitamin D can pose health risks. Low blood levels of the vitamin have been associated with the following:

• increased risk of death from cardiovascular disease
• cognitive impairment in older adults
• severe asthma in children
• cancer

Research suggests that vitamin D could play a role in the prevention and treatment of a number of different conditions, including type 1 and type 2 diabetes

Causes of vitamin D deficiency

The Department of Health says a significant proportion of people in the UK have low vitamin D levels. This has resulted in a rising number of cases of rickets in children and osteomalacia in adults.

Vitamin D deficiency can occur for a number of reasons, including:

• You do not consume the recommended levels of the vitamin over time. This is likely if you follow a strict vegetarian or vegan diet because most of the natural sources are animal-based, including fish and fish oils, egg yolks, cheese, and beef liver.
• Your exposure to sunlight is limited. Because the body makes vitamin D when your skin is exposed to sunlight, you may be at risk of deficiency if you are housebound, live in northern latitudes, wear long robes or head coverings for religious reasons, or have an occupation that prevents sun exposure.
• You have dark skin. The pigment melanin reduces the skin's ability to make vitamin D in response to sunlight exposure. Some studies show that older adults with darker skin are at high risk of vitamin D deficiency.
• Your kidneys cannot convert vitamin D to its active form. As people age their kidneys are less able to convert vitamin D to its active form, thus increasing their risk of vitamin D deficiency.
• Your digestive tract cannot adequately absorb vitamin D. Certain medical problems, including Crohn's disease, cystic fibrosis and coeliac disease, can affect your intestine's ability to absorb vitamin D from the food you eat.
• You are obese. Vitamin D is extracted from the blood by fat cells, altering its release into the circulation. People with a body mass index (BMI) of 30 or greater often have low blood levels of vitamin D.