Sunday, November 14, 2010
Every cell in the body has a vitamin D receptor protein. It's estimated that upwards of 2,000 genes are directly or indirectly regulated by vitamin D.
It’s known that vitamin D is necessary for proper bone formation and maintenance. But recent decades have seen a torrent of studies suggesting that vitamin D can also affect many other aspects of health; some scientists have come to consider the daily recommended intake of 400 international units of vitamin D far too low. Michael Holick is a biochemist and endocrinologist at Boston University who has spent a career researching the effects of vitamin D (which is actually not a vitamin but a hormone precursor).
How much vitamin D do we need?
Children should be taking at least 400 to 1,000 international units of vitamin D as a supplement every day, and adults should take 1,500 to 2,000 IU.
What about pregnant or breast-feeding women?
We tested pregnant women who were taking a prenatal vitamin containing 400 IU of vitamin D each day and drinking two glasses of fortified milk, and found that 76 percent of them — and 81 percent of their newborns — were still vitamin D deficient at the time of giving birth. We also estimate that most breast-feeding women are vitamin D deficient, and they pass along deficient milk to their infants.
Vitamin D deficiency has been linked to increased risks of infectious diseases, cancer, autoimmune diseases, heart disease, cognitive decline, Parkinson’s disease, asthma, mood disorders and even diabetes. Is there biological evidence to show how vitamin D could influence so many conditions?
For example, we know that immune cells called macrophages activate vitamin D, which causes cells to make defensin proteins that specifically kill infective agents like tuberculosis bacteria. A Japanese study recently found that children receiving 1,200 IU of vitamin D each day reduced their risk of getting the flu by almost 50 percent. Every tissue and every cell in the body has a vitamin D receptor protein. It’s estimated that upwards of 2,000 genes are directly or indirectly regulated by vitamin D.
Have there been clinical trials showing the utility of vitamin D?
Absolutely. For instance, a trial of postmenopausal women showed that taking vitamin D over four years reduced their risk of cancer by 60 percent.
Vitamin D is a group of fat-soluble secosteroids, the two major physiologically relevant forms of which are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D without a subscript refers to either D2 or D3 or both. Vitamin D3 is produced in the skin of vertebrates after exposure to ultraviolet B light from the sun or artificial sources, and occurs naturally in a small range of foods. In some countries, staple foods such as milk, flour and margarine are artificially fortified with vitamin D, and it is also available as a supplement in pill form.
Food sources such as fatty fish, mushrooms, eggs, and meat are rich in vitamin D and are often recommended for consumption to those suffering vitamin D deficiency.
Vitamin D is carried in the bloodstream to the liver, where it is converted into the prohormone calcidiol. Circulating calcidiol may then be converted into calcitriol, the biologically active form of vitamin D, either in the kidneys or by monocyte-macrophages in the immune system. When synthesized by monocyte-macrophages, calcitriol acts locally as a cytokine, defending the body against microbial invaders.
When synthesized in the kidneys, calcitriol circulates as a hormone, regulating, among other things, the concentration of calcium and phosphate in the bloodstream, promoting the healthy mineralization, growth and remodeling of bone, and the prevention of hypocalcemic tetany. Vitamin D insufficiency can result in thin, brittle, or misshapen bones, while sufficiency prevents rickets in children and osteomalacia in adults, and, together with calcium, helps to protect older adults from osteoporosis. Vitamin D also modulates neuromuscular function, reduces inflammation, and influences the action of many genes that regulate the proliferation, differentiation and apoptosis of cells..
Dietary supplement, also known as food supplement or nutritional supplement, is a preparation intended to supplement the diet and provide nutrients, such as vitamins, minerals, fiber, fatty acids, or amino acids, that may be missing or may not be consumed in sufficient quantity in a person's diet. Some countries define dietary supplements as foods, while in others they are defined as drugs or natural health products.
Supplements containing vitamins or dietary minerals are included as a category of food in the Codex Alimentarius, a collection of internationally recognized standards, codes of practice, guidelines and other recommendations relating to foods, food production and food safety. These texts are drawn up by the Codex Alimentarius Commission, an organization that is sponsored by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO).
'17th century diseases' caused by low levels of vitamin D, is rearing its ugly head in Britain after 80 years, and modern lifestyle is to blame.
It is thought that extensive use of sunscreens, children playing computer games and watching TV rather than being outdoors and a poor diet are to blame.
Children from all backgrounds are being affected now and the disease is not limited to the poor as it was in Victorian times, reports the Telegraph.
Nicholas Clarke, professor of paediatric orthopaedic surgery at the University of Southampton in UK, and colleague Justin Davies, paediatric endocrinologist, have checked over 200 children for bone problems.
More than 20 percent of them have significant deficiencies. "A lot of the children we've seen have got low vitamin D and require treatment," said Clarke.
"This is almost certainly a combination of the modern lifestyle, which involves a lack of exposure to sunlight, but also covering up in sunshine, and we're seeing cases that are very reminiscent of 17th century England."
Prof Clarke says vitamin D supplements should be more widely adopted to halt the rise in cases. Vitamin D is found in oily fish and eggs and margarine, cereals and milk can be fortified with it.
The vitamin is vital for the absorption of calcium needed for strong bones and teeth.