Vitamin D is not just important for building strong bones; it also plays an essential role in the body's fight against infections such as tuberculosis, an international research team including UCLA scientists has found. Tuberculosis, a potentially fatal lung disease, causes an estimated 1.8 million deaths annually, according to the World Health Organization, and it especially impacts those with reduced immunity, such as HIV-infected individuals. In an interesting twist, people with darker skin traditionally have had a higher susceptibility to tuberculosis, and areas of Africa lead the world with the highest infection rates. Scientists believe this may be partly due to the skin pigment melanin. Melanin is more abundant in darker skin, which helps shield the body from ultraviolet rays; however, it also reduces Vitamin D production.
Vitamin D — a natural hormone, rather than a vitamin — is known to be instrumental in bone development but also may protect against cancer, autoimmune diseases, and infections. In a study published online October 12 in the journal Science Translational Medicine, researchers examined the mechanisms that govern the immune system's ability to kill or inhibit the growth of pathogens such as Myobacterium tuberculosis, the bacteria that causes tuberculosis. The researchers found that T cells, which are white blood cells that play a central role in immunity, release a protein called interferon-g that triggers communication between cells and directs infected immune cells to attack the invading tuberculosis bacteria. However, this activation requires sufficient levels of Vitamin D to be effective. They next tested serum taken from blood samples in healthy humans, both with and without sufficient levels of Vitamin D. They found that the immune response was not triggered in the serum with lower Vitamin D levels, as is found in many African Americans. However, when adequate Vitamin D was added to this deficient serum, the immune response was effectively activated.
The team found that there was an 85% reduction of colony-forming tuberculosis bacteria in human macrophage cells that were effectively treated with interferon-g in the presence of sufficient Vitamin D. The team noted that Vitamin D may help both innate and adaptive immunity, two systems that work synergistically together to fight infections.
Previous research by the team found that Vitamin D played a key role in the production of a molecule called cathelicidin, which helps the innate immune system kill the tuberculosis bacteria. Humans are born with innate immunity, which is the preprogrammed part of the immune system. The current research findings demonstrate that vitamin D is also critical for the action of T cells, key players in adaptive immunity, a highly specialized system that humans acquire over time as they encounter different pathogens.
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