In the 1800s, clinical trials administering cod liver oil (a source of Vitamin D) to tuberculosis patients provided early evidence of its clinical benefit. In 1859, sanatoriums used heliotherapy (exposure to sunlight) as a means to increase tuberculosis patient’s vitamin D intakes. And in case you’re wondering, Vitamin D exerts its effect by binding to and modulating key members of the immune system including T cells, B cells, macrophages and dendritic cells.
I learned about this fact from:
AR Martineau. 2012. Old wine in new bottles: vitamin D in the treatment and prevention of tuberculosis. Proceedings of the Nutrition Society, 71, 84-89.http://journals.cambridge.org/download.php?file=%2FPNS%2FPNS71_01%2FS0029665111003326a.pdf&code=09e65cdc6b159acb91f4e05f6aebbcf2
J Rodrigo Mora, M Iwata, U von Andrian. 2008. Vitamin effects on the immune system: vitamins A and D take center stage. Nat Rev Immunol, 8(9)685-698. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2906676/pdf/nihms185109.pdf