The Infection-Fighting Gift of the Sun

Henry Lindlahr (1862-1924), one of the fathers of the North American natural health movement, wrote, "Everything that draws the breath of life depends for vital energy on the life-giving rays of the sun."(1) Indeed, Lindlahr recommended sunbathing as part of his, "General Regimen for Wholesome Living and for Prevention of Disease." In 1903, Niels Finsen won the Nobel Prize for Physiology or Medicine for his use of concentrated light therapy in the treatment of various diseases, including smallpox and lupus vulgaris.(2) By the 1920s, heliotherapy was an accepted treatment for tuberculosis both in Europe and the U.S.(3)

Modern science is now looking at the molecular basis for the amazing ability of the sun to fight infection. The search is focusing on antimicrobial peptides, which are found on epithelial surfaces and in circulating white blood cells. These antimicrobial peptides (AMPs) serve to kill bacteria, viruses, fungi, protozoa and other microorganisms responsible for infectious disease. The gene encoding one such AMP, called LL-37, has recently been found to contain sites for the vitamin D receptor.(3) Why would a gene for an antimicrobial peptide be turned on by vitamin D?

The answer apparently lies in beautifully orchestrated physiology featuring immune suppression and microbial defense.Vitamin D is known to suppress the immune system by several mechanisms, including those of inhibiting the activity of Langerhans cells and inhibiting the induction of T helper type 1 cells.(3) It seems that as a compensatory response, vitamin D then increases the powerful antimicrobial peptide LL-37 in the event that harmful microorganisms present themselves.(3)

Clinical correlation of this bench science may not be far away. In a recent issue of Science Express, Liu, et al(4) reported evidence for the role of vitamin D and AMPs in the higher attack rate of tuberculosis in dark-skinned versus light-skinned people.

(1) Lindlahr H. Natural Therapeutics, Volume II: Practice. Saffron Walden, Essex, England: The C.W. Daniel Company Limited, 1919.
(2) http://nobelprize.org/medicine/laureates/1903/press.html
(3) Zasloff M. Fighting infections with vitamin D. 2006 Nature Medicine 12(4):388-390.
(4) Liu PT, Stenger S, Li H, et al. Toll-like receptor triggering of a vitamin D-mediated human antimicrobial response. Science Express published online 22 February 2006 (DOI:10.1126/science.1123933).