Sunlight exposure in association with risk of lymphoid malignancy: a meta-analysis of observational studies

Several observational studies have shown contradictory results regarding the association between sunlight exposure and the risk of malignant lymphoma. Thus, we aimed to systematically determine the association between sunlight exposure and lymphoid malignancy risk through a meta-analysis.

A thorough search of four electronic databases (PubMed, Embase, Web of Science, and Scopus) was performed to identify eligible studies until 13 August 2020. A random-effects model was used to calculate risk estimates of sunlight exposure. The main outcome measure was the risk of lymphoid malignancy subtypes with odds ratios (ORs) and 95% confidence intervals (CIs) according to various forms of solar ultraviolet radiation.

In total, 17 case-control studies and 9 cohort studies including 216,285 non-Hodgkin lymphoma (NHL) and 23,017 Hodgkin's lymphoma (HL) patients were included in the final analysis. Personal sunlight exposure was significantly associated with a decreased risk of HL (OR 0.77; 95% CI 0.68-0.87) and NHL (OR 0.81; 95% CI 0.71-0.92), including all subtypes except T-cell lymphoma. Ambient sunlight exposure at residence was associated with a reduced risk of HL (OR 0.88; 95% CI 0.81-0.95) and all NHL subtypes (OR 0.84; 95% CI 0.73-0.96), except for chronic lymphocytic leukemia/small lymphocytic lymphoma. As the number of sunburns and sunbaths increased, the risk of NHL tended to decrease.

While there was an observed protective effect both from case-control and prospective studies, substantial heterogeneity was found in the current study. Thus, more evidence is required to confirm that promoting sunlight exposure can prevent the development of lymphoid neoplasia.