What do we need vitamin D for?
It is crucial for the absorption and metabolism of calcium and phosphorous, which have various functions, especially the maintenance of healthy bones.
It is an immune system regulator.
It may be an important way to arm the immune system against disorders like the common cold, say scientists from the University of Colorado Denver School of Medicine, Massachusetts General Hospital and Children's Hospital Boston.
It may reduce the risk of developing multiple sclerosis. Multiple sclerosis is much less common the nearer you get to the tropics, where there is much more sunlight, according to Dennis Bourdette, chairman of the Department of Neurology and director of the Multiple Sclerosis and Neuroimmunology Center at Oregon Health and Science University, USA.
Vitamin D may have a key role in helping the brain to keep working well in later life, according to a study of 3000 European men between the ages of 40 and 79.
Vitamin D is probably linked to maintaining a healthy body weight, according to research carried out at the Medical College of Georgia, USA.
It can reduce the severity and frequency of asthma symptoms, and also the likelihood of hospitalizations due to asthma, researchers from Harvard Medical School found after monitoring 616 children in Costa Rica.
It has been shown to reduce the risk of developing rheumatoid arthritis in women.
A form of vitamin D could be one of our body's main protections against damage from low levels of radiation, say radiological experts from the New York City Department of Health and Mental Hygiene.
Various studies have shown that people with adequate levels of vitamin D have a significantly lower risk of developing cancer, compared to people with lower levels. Vitamin D deficiency was found to be prevalent in cancer patients regardless of nutritional status, in a study carried out by Cancer Treatment Centers of America.
High vitamin D doses can help people recover from tuberculosis more rapidly, researchers reported in September 2012 in the Proceeding of the National Academy of Sciences (PNAS).
An additional study published in September 2012 suggested that low levels of vitamin D may increase the risk of heart attack and early death.
Vitamin D and nutrition
Over the last few hundred years human lifestyles have changed. The industrial revolution resulted in more indoor work and less exposure to sunlight. Many societies around the world wore more clothing over the centuries, further reducing skin exposure to sunlight. These changes have brought with them a significant reduction in the natural production of vitamin D and subsequent diseases.
Countries responded to these changes by fortifying some foods with vitamins D2 and D3, examples include breakfast cereals, bread, pastries, oil spreads, margarine, milk and other dairy products. Initially, some scientists complained that nutritional fortification and recommended supplementation doses were not making up for the shortfall. These people were ignored, and sometimes ridiculed - however, over the last few years studies indicate that they may have been right after all.
Not that many foods contain vitamin D. Some fish, such as salmon, tuna and mackerel, as well as fish liver oils are considered to be the best sources. Some vitamin D is also present in beef liver, cheese and egg yolks. Most of these are Vitamin D3. Some mushrooms provide variable amounts of vitamin D2.
Most of the food sourced vitamin D in the western diet comes from fortified foods - where vitamin D is artificially added. Most US milk is fortified with 100 IU/cup of vitamin D. In the 1930s milk was fortified in many countries to combat rickets, which was a major health problem then.
Excerpts from http://www.medicalnewstoday.com/articles/161618.php