Good food sources
Vitamin D is composed of several closely related substances that are present mainly in foods of animal origin, such as fatty fish, cod liver oil, eggs, milk, butter and cheese, but small amounts also occur in dark, green, leafy vegetables and mushrooms. It is sometimes known as the 'sunshine vitamin', as it can be manufactured in skin that is exposed to the sun without sunscreen. It is, therefore, a good idea to increase the amount taken in food during the winter. It can be stored in the body, so it is not essential to eat it every day.
Vitamin D helps to maintain healthy bones and teeth and effective muscle junction by regulating the levels of calcium and phosphorus in the body. In addition, it is needed to keep the heart and nervous system healthy, and to enable the blood to clot normally.
What if your intake is too low?
Vitamin D deficiency in growing children causes rickets, a condition in which the muscles develop poorly and the bones are too soft. The weight-bearing bones of the legs bend, causing either bowed legs or knock-knees. In adults, loss of bone minerals from vitamin D deficiency causes osteomalacia, in which the bones are painful and tender, the muscles are weak and deafness develops. In older people, osteoporosis can occur when protein is lost from the bone in addition to the mineral loss. This is usually painless in its early stages.
When extra may be needed
- If your skin is rarely exposed to sunlight (for example, night workers and those who regularly wear protective or all-enveloping clothing or uniform)
- By elderly people, especially in winter
- When you are pregnant or breast feeding
- If you live in an area where there is smog
- If you spend a large amount of time indoors
- If your skin is dark and you live in an area of little natural sunlight
- If you are a vegan
(Pregnant and breast feeding women should consult a doctor, midwife, or qualified nutritional therapist before taking any vitamin or mineral supplements.)
Can too much be toxic?
Too much vitamin D causes elevated levels of calcium in the blood, and results in drowsiness, nausea, weakness, excessive thirst, abdominal pain and a general feeling of malaise. Prolonged exposure to the sun can cause toxicity in white people whose skin is not already tanned (the dark outer skin shades the deeper layers of skin where the vitamin D is produced). In the longer term, calcium is deposited in the soft tissues of the body, including the walls of the blood vessels and the kidneys, where it can cause serious damage.
Using a supplement
If you have sarcoidosis, do not take vitamin 0 supplements without consulting your doctor.