Chang ET, Canchola AJ, Cockburn M, et al. Adulthood residential ultraviolet radiation, sun sensitivity, dietary vitamin D, and risk of lymphoid malignancies in the California Teachers Study. Blood. 2011;118:1591-1599.
Prospective cohort study that examined the association between residential ambient ultraviolet radiation (UVR) exposure and incidence of lymphoid malignancies. In 1995–1996, participants filled out a questionnaire that evaluated various risk factors for cancer. Average daily UVR exposure was estimated for each participant based on their residential address at baseline. The women were followed until December 31, 2007.
The cohort consisted of 121,216 active and retired female public school teachers participating in the California Teachers Study.
Incidence of lymphoid malignancies (non-Hodgkin lymphomas, multiple myeloma, and Hodgkin lymphoma)
During the follow-up period, 629 women were diagnosed with non-Hodgkin lymphomas, 119 with multiple myeloma, and 38 with Hodgkin lymphoma. Higher residential UVR levels within a 20-km radius were associated with lower risk of overall non-Hodgkin lymphomas; the relative risk (RR) comparing the highest and the lowest statewide quartiles of minimum UVR was 0.58 (95% confidence interval [CI], 0.42–0.80). RRs (95% CIs) were 0.36 (0.17–0.78) for diffuse large B-cell lymphoma, 0.46 (0.21–1.01) for chronic lymphocytic leukemia/small lymphocytic lymphoma, and 0.57 (0.36–0.90) for multiple myeloma. These associations were not modified by skin sensitivity to sunlight, race/ethnicity, body mass index, or neighborhood socioeconomic status. Dietary vitamin D intake also was not associated with risk of lymphoid malignancies.
While excessive UVR exposure is clearly undesirable, the results of the present study support other evidence indicating that spending a moderate amount of time in the sun can be beneficial.
Although observational studies cannot prove cause-and-effect, the results of this study are consistent with the possibility that sunlight exposure prevents the development of lymphoid malignancies. The mechanism of this possible protective effect is not clear. UVR exposure has multiple physiological effects (aside from vitamin D synthesis), including the production of corticotrophin-releasing hormone (an immunomodulating agent) in the skin, and possible stimulation of the hypothalamic-pituitary axis through the retina. While in vitro studies suggest that vitamin D might help prevent the development of lymphomas, a meta-analysis of 10 prospective cohort studies found no association between serum 25-hydroxyvitamin D levels and risk of non-Hodgkin lymphoma. Moreover, in the present study there was no association between dietary vitamin D intake and risk of lymphoid malignancies. Those findings suggest that any protective effect of UVR exposure against lymphoid cancer is not due to vitamin D.
The American Academy of Dermatology has recommended that people essentially avoid all sunlight exposure, in order to prevent skin cancer. However, considering that sun exposure has been a constant throughout human history, the idea that we should avoid sunlight completely is counterintuitive. While excessive UVR exposure is clearly undesirable, the results of the present study support other evidence indicating that spending a moderate amount of time in the sun can be beneficial.