March 8, 2010

Why Vitamin D Is Essential

As much as half the world's population has less than adequate immune systems where their killer T cells cannot fight infection properly, and scientists find that vitamin D is a vital key to keeping their defenses up.

Danish researchers have found that vitamin D could help with the fight against infectious diseases and worldwide epidemics, and could be very useful in finding new vaccines, they said.

The researchers found that T cells in people's immune systems rely on vitamin D to become active to help stave off infections. Without vitamin D, those cells remain dormant and unaware of possible infection or pathogen threats.

"When a T cell is exposed to a foreign pathogen, it extends a signaling device or 'antenna' known as a vitamin D receptor, with which it searches for vitamin D," said Carsten Geisler of Copenhagen University's department of international health, immunology and microbiology, who led the study. "This means the T cell must have vitamin D or activation of the cell will cease. If the T cells cannot find enough vitamin D in the blood, they won't even begin to mobilize."

Scientists have long known that vitamin D is important for calcium absorption, but what they didn't know was how crucial it is for actually activating the immune system. "Now we know," Geisler said in the study which appears in the journal Nature Immunology.

Most vitamin D is made by the body as a natural by-product of the skin's exposure to the sun. It is also found in fish liver oil, eggs and fatty fish. Vitamin D is also commonly taken as a daily supplement usually in pill form.

With nearly half the world's population having less than adequate levels of vitamin D, scientists say the problem will continually get worse as people spend more and more time indoors.

Geisler said the research findings offered valuable information about the immune system and how vitamin D could help with other areas of health science as well. "This is important not only in fighting disease but also in dealing with anti-immune reactions of the body and the rejection of transplanted organs," the authors wrote.

Although T cells are important infection fighting cells, they multiply very quickly and sometimes accidentally attack the body itself. In organ transplants, for example, T cells can attack the new organ because it views it as a "foreign invader". In AIDS cases, T cells mistake the body's own cells as threats, which prompts the body to attack itself.

There is no authoritative studies on vitamin D intake, but most experts recommend 25 to 50 micrograms daily, said Geisler.


Image 1: T lymphoycte cell (small cell with red surface) scanning another cell for the presence of foreign molecules. Credit: Professor Carsten Geisler

Image 2: When the naïve T cell recognizes foreign molecules with its T cell receptor (TCR) it sends activation signals (1) to the VDR gene. The VDR gene now starts the production of VDR (2). VDR binds vitamin D in the T cell (3) and becomes activated. Vitamin D bound to activated VDR goes back into the cell nucleus and activates the gene for PLC-gamma1 (5). PLC-gamma1 is produced (6) and the T cells can get started. Credit: Professor of Immunology, Carsten Geisler


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