Vitamin D controls levels of calcium in the body and is important for good health, growth and strong bones. Low levels of vitamin D (vitamin D deficiency) in children can cause a bone condition called rickets. Vitamin D deficiency in adults can lead to weak, fragile bones and muscle weakness.
Vitamin D is very important for our health. The main action of vitamin D is to make sure enough of the calcium in our diet is absorbed from our gut (bowel). This is very important because calcium is needed to keep bones healthy and strong. Vitamin D is also important for our muscles to work properly and for our general health.
As well as bone and muscle health, vitamin D deficiency is associated with a number of different conditions. These conditions include diabetes, coronary heart disease, breast cancer, bowel cancer, Alzheimer's disease and many others. The exact significance of these associations isn't yet properly understood.
What is vitamin D?
Vitamin D is a vitamin and, like all vitamins, it is essential for our health and well-being. Vitamin D is mostly made in the skin by exposure to sunlight. Most foods contain very little vitamin D naturally. Foods that naturally contain vitamin D include:
- Oily fish (such as sardines, pilchards, herring, trout, tuna, salmon and mackerel).
- Egg yolk, red meat and liver.
Some foods are fortified with vitamin D (this means they have vitamin D added to them). These foods include infant formula milk, most margarines and some cereals. All milk is fortified with vitamin D in some countries but not in the UK.
Who's at risk of deficiency?
Vitamin D deficiency means that there is not enough vitamin D in your body. This can occur for three main reasons:
- The body has an increased need for vitamin D - for example, during pregnancy and when breast-feeding.
- The body is unable to make enough vitamin D - for example, people who get very little sunlight, the elderly and people with dark skin.
- Not enough vitamin D is being taken in the diet. Vitamin D deficiency is more likely to occur in people who follow a strict vegetarian or vegan diet, or a non-fish-eating diet.
Read more about causes of vitamin D deficiency.
How common is vitamin D deficiency?
A lack of vitamin D is very common. One survey in the UK showed that about 1 in 5 adults and about 1 in 5 children in the UK have low vitamin D levels. More people have low vitamin D levels in the winter and spring because of less exposure to sunlight.
What symptoms does it cause?
Many people with a mild lack of vitamin D have no symptoms, or may complain of only vague ones such as tiredness or general aches. A more severe lack can cause serious problems such as rickets (in children) and osteomalacia (in adults).
Find out more about the symptoms of vitamin D deficiency.
How is vitamin D deficiency diagnosed?
It may be suspected from your medical history, symptoms, or lifestyle. A simple blood test for vitamin D level can make the diagnosis. Blood tests for calcium and phosphate levels and liver function may also show changes linked to a low level of vitamin D. Sometimes a wrist X-ray is done for a child in order to see how the bones are developing. This can assess how severe the problem is by looking for changes in the wrist bones.
What is the treatment?
Learn more about the options for treating vitamin D deficiency.
How can I avoid being deficient?
To prevent vitamin D deficiency, it's important to get enough exposure to sunlight. Some people are at more risk than others and it's recommended they take vitamin D supplements all year round. These include:
- All pregnant and breast-feeding women.
- All babies and young children aged 6 months to 5 years.
- Anyone aged 65 years or over.
- People who don't get much sun exposure.
Read more about how you can prevent vitamin D deficiency.
What is the outlook?
The outlook (prognosis) is usually excellent. Both the vitamin levels and the symptoms usually respond well to treatment. However, it can take time (months) for bones to recover and for symptoms such as pain to improve.
The complications of severe deficiency have been mentioned. Rickets can occur in children, and osteomalacia in adults. These diseases affect the strength and appearance of bones, and can lead to permanent bone deformities if untreated or if treatment is delayed.
Further reading and references
Vitamin D and health; Scientific Advisory Committee on Nutrition (July 2016)
Evaluation, Treatment, and Prevention of Vitamin D Deficiency; Endocrine Society Clinical Guideline (July 2011)
Vitamin D - advice on supplements for at risk groups; Chief Medical Officers of the UK, February 2012
Bolland MJ, Avenell A, Grey A; Should adults take vitamin D supplements to prevent disease? BMJ. 2016 Nov 23355:i6201. doi: 10.1136/bmj.i6201.
Vitamin D: increasing supplement use among at-risk groups; NICE Public Health Guidance, November 2014
Sunlight exposure: risks and benefits; NICE Guidance (February 2016)
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