Washington, Aug 19 - 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, expressing concern that over 50 percent of US citizens are deficient in 'the sunshine vitamin'.

'The existence and importance of this part of our immune response makes it clear that humans 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.