With an estimated 70% of Americans have insufficient levels of Vitamin D and nearly 1 billion people worldwide are deficient in the nutrient, Oregon State University (USA) researchers warn of the impending public health problem of Vitamin D deficiency in both developed and developing nations.  Oregon State University scientists have discovered that vitamin D induces the expression of cathelicidin, an antimicrobial peptide gene.  The team posits that this mechanism is partly responsible for vitamin D’s capacity to function as one’s primary immune response, and that future advances in the use of cathelicidin may form the basis for new immune-based therapies.  While Vitamin D can be obtained from the diet, experts suggest that food sources are rarely adequate. In fact, most people get the bulk of this fat-soluble vitamin from the UV-B radiation in sun exposure, which naturally causes the skin to produce it. However, people living north of about 40 degrees latitude – a geography encompassing a large portion of the United States and northern Europe –are often deficient after months of inadequate winter sunshine.