Objectives: The aims of this study were to determine if ultraviolet light (UV) is immunosuppressive in healthy older males, if beta-carotene (betaC) supplementation could prevent any observed UV-induced immunosuppression, and to compare these effects with those observed previously in younger men.
Methods: The study was a placebo-controlled, randomized trial that employed a 2 x 2 factorial design. Healthy older men (mean age 65.5 years) received 30 mg betaC or placebo daily throughout the 47-day trial, while on a low carotenoid diet. After 28 days, half of each group received 12 suberythemic exposures to UV over a 16-day period. Delayed-type hypersensitivity (DTH) tests and plasma carotenoid assays were performed at baseline, pre-UV and post-UV time points, with DTH testing performed on an area of skin protected from UV exposure.
Results: UV exposure resulted in significantly suppressed DTH response in the placebo group but not in the betaC-UV group. While there was no significant interaction between betaC supplementation and UV on DTH response, there was a significant inverse relationship between final plasma betaC concentration and extent of UV-induced suppression of DTH response. A similar correlation existed among subjects not exposed to UV.
Conclusions: Suberythemic UV exposure was immunosuppressive, as measured by DTH response, in healthy older men as in younger men. Higher plasma betaC was significantly associated with maintenance of DTH response, although the extent of protective effect of betaC appeared less than previously observed in younger subjects. The attenuated effect of betaC in the older UV-exposed subjects may have resulted in part from muted plasma betaC responses to betaC supplementation and/or higher plasma vitamin E levels than those of younger men. The finding that stronger DTH responses were associated with higher plasma betaC concentrations in both UV and non-UV subjects further supports a role for this nutrient in immunomodulation.