Vitamin D status and risk of non-Hodgkin lymphoma: An updated meta-analysis

This meta-analysis aimed to extensively investigate the association between various measures of vitamin D status and non-Hodgkin lymphoma (NHL) and its subtypes. We searched MEDLINE (PubMed), Embase, and the Cochrane Library in February 2018. Two authors independently reviewed and selected articles based on predetermined criteria. A total of 30 studies with 56,458 NHL cases were finally selected, with 24, 9, and 3 studies on sunlight/ultraviolet radiation (UVR) exposure, dietary intake, and serum/plasma 25-hydroxyvitamin D levels, respectively. Significant protective effects of overall sunlight/UVR exposure on NHL and subtypes were observed, with summary relative risks (RRs) ranging from 0.67-0.80 (RR for NHL = 0.80; 95% confidence interval [CI]: 0.71-0.90) among subjects with high exposure compared to those with low exposure. The results were consistent with various classifications of sunlight/UVR exposure. In contrast, when exposure measures of dietary vitamin D intake (RR for NHL = 1.03; 95% CI: 0.90-1.19) and serum/plasma 25-hydroxyvitamin D levels (RR for NHL = 0.97; 95% CI: 0.82-1.15) were used, risk estimates were inconsistent or non-significant for NHL and the subtypes. While risk estimates varied by different measures of vitamin D status, a protective effect of sunlight/UVR exposure on NHL incidence was verified, across most of the tested subtypes as well as exposure categories.