He coauthored a 2009 study concluding that vitamin D activates an enzyme on the surface of monocytes and keratinocytes, increasing the cells' pattern recognition and boosting their antimicrobial effect. "This enhances the immune barrier in injured skin," Dr. Gallo said (J. Clin. Invest. 2007;117:803-11).
Animal models also "show quite clearly that the extent of infection can be limited in an animal supplemented with vitamin D compared to a deficient one," he added. "There also seems to be a relative association between viral infections and upper respiratory infections, with the highest incidence occurring at the lowest levels of vitamin D on a seasonal basis. So maybe Schlitz did have an idea there. Therefore I’d say Myth No. 4 is plausible, but not yet clearly defined."
Dr. Gallo did not have any relevant financial disclosures. However, he is a member of the Institute of Medicine’s committee on Dietary Reference Intakes for Vitamin D and Calcium. The committee will release new recommendations for national daily requirements of vitamin D and calcium later this year.