The ability of vitamin D to regulate anti-bacteria proteins, a key part of the immune system of humans and primates, has survived through 60 million years of evolution. This suggests that it must be critical to their survival, researchers say, express concern that over 50 per cent of US citizens are deficient in "the sunshine vitamin".

"The existence and importance of this part of our immune response makes it clear that human and other primates need to maintain sufficient levels of vitamin D," said Adrian Gombart, associate professor of biochemistry and principal study investigator at Oregon State University (OSU).

Researchers from OSU and the Cedars-Sinai Medical Centre describe the presence of a genetic element that's specific to primates and involved in the innate immune response.

The genetic material -- called Alu -- is part of what used to be thought of as "junk DNA" and makes up more than 90 percent of the human genome.

Alu, however, is now understood to often play important roles in regulating and "turning on" the expression of other genes.

In this case, the genetic element is believed to play a major role in the proper function of the "innate" immune system in primates -- an ancient, first line of defence against bacteria, viruses and other pathogens, in which the body recognises something that probably doesn't belong there.

"Many people are familiar with the role of our adaptive immune system, which is what happens when we mount a defence against a new invader and then retain antibodies and immunity in the future," Gombart said, according to an OSU release.

In primates, this action of "turning on" an optimal response to microbial attack only works properly in the presence of adequate vitamin D, which is actually a type of hormone that circulates in the blood and signals to cells through a receptor.

The study was published in the BMC Genomics.

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