Vitamin D and Health
~ October 2003 No.173 ~
Vitamin D is called the sunshine vitamin because the human skin synthesizes vitamin D when it is exposed to sunlight. When humans wore fewer clothes and were out of doors more, this was not a problem. However, in modern western society our time in the sun is often restricted to the occasional visit to the beach. Even then, sun screens cut down on our exposure to the sun, which is good to prevent skin cancer, but could be lowering the production of Vitamin D. It has been estimated that 10-15 minutes of sunshine 3 times a week is sufficient exposure to produce most people's requirement for vitamin D. Those living in northern regions are often at greater risk as are those who are housebound.
Vitamin D is a fat soluble vitamin. This means that it must be dissolved in oil to be absorbed into the body. It is most commonly found it foods that are also sources of oil (fat) such as certain fish, egg yolk, some vegetable oils, and fatty fish such as salmon and tuna. This presents a problem when people are trying to cut down on the fat content in their diet. They may simultaneously be reducing their vitamin D intake. Disease conditions that reduce fat absorption such as pancreatic enzyme deficiency, Crohn's disease, cystic fibrosis, sprue, and some forms of liver disease can also lead to vitamin D deficiency.
Vitamin D helps the body absorb calcium and plays a role in the development of bones and teeth. A deficiency of vitamin D can lead to soft bones or rickets. It now appears that low vitamin D status is involved in the onset of osteoporosis. Vitamin D also is involved in the regulation of the levels of calcium and phosphorus in the blood.
Recently vitamin D has been implicated in other health / disease states that may go beyond its relationship with calcium and bones. Intervention studies have shown that vitamin D or some of the compounds derived from vitamin D can 1) reduce blood pressure in hypertensives 2) improve blood glucose levels in diabetics 3) improve symptoms of rheumatoid arthritis and multiple sclerosis. There are preliminary studies ttat indicate that low vitamin D intake may lead to increased risk of prostrate, breast, colon and other cancers.
Breast fed babies are particularly sensitive population to Vitamin D deficiency.. Human breast milk is low in vitamin D and this, together with the trend to breast feed longer, has raised concerns. If the vitamin D status of the mother is low, this only magnifies the poor nutrition of the breast feeding baby.
Milk with added vitamin D still appears to be the most common source of this important vitamin. Therefore adolescents and young women of reproductive age should ensure that they are getting enough vitamin D. For many people a daily supplement that contains vitamin D may be the best way to ensure good vitamin D status.
Vitamin D in preventive medicine: are we ignoring the evidence?
British Journal of Nutrition, volume 89, 552-572