Topical riboflavin attenuates ultraviolet B‐ and ultraviolet A‐induced immunosuppression in humans

Background: Riboflavin (vitamin B₂) plays a key role in cellular energy metabolism. We have observed previously that nicotinamide (vitamin B₃), which is also centrally involved in cellular energy restoration after UV irradiation, is highly immune protective in humans. We thus hypothesized that riboflavin might also confer immune protection. Methods: We irradiated healthy, nickel‐allergic volunteers with narrowband UVA (385 nm) and UVB (300 nm) at separate sites on the lower back. These areas were treated with riboflavin solution or vehicle at 24 h and again at 30 min before UV exposure. Forty‐eight hours after irradiation, volunteers were patch tested with nickel‐containing Finn chambers, at both irradiated and nonirradiated sites, with and without prior riboflavin treatment. The resulting contact hypersensitivity reactions at each site were then measured 72 h later with a reflectance erythema meter in order to determine and compare the immune suppressive effects of each intervention. Results: We observed that low doses of both UVB and longwave UVA1 were immune suppressive in humans. Topical riboflavin conferred immune protection against both wavebands. Conclusions: Riboflavin is immune protective in humans, and this may reflect the role of the B group vitamins in cellular energy restoration after UV exposure.