Diabetes mellitus (DM) is thought to be associated with an increased risk of non-Hodgkin's lymphoma (NHL), although the evidence so far remains inconsistent. Thus, our study aimed to further assess this association.

Electronic searches were performed of the PubMed, Web of Science and Embase databases up to 11 March 2019. A random-effects model was used to calculate summary relative risks (RRs) with corresponding 95% confidence intervals (CIs).

A total of 20 articles including data from 35 cohort studies matched our inclusion criteria, and 31 RRs were calculated for type 2 DM; the summary RR was 1.20 (95% CI: 1.12–1.30, I² = 84.7%). Also, four RRs were calculated for type 1 DM, and the result was significant (RR: 1.55, 95% CI: 1.15–2.08, I² = 0.0%). The results of subgroup analyses demonstrated that the association between DM and NHL was much more substantial in an Asian population, while sensitivity analyses suggested the robustness of a positive association between DM and NHL risk. In addition, the RR of NHL correlated negatively with duration of DM, with the highest risk found in patients within 1–2 years of DM diagnosis.

Our study findings suggest a moderate increase in risk of NHL in type 1 and 2 DM patients. Future studies should investigate the effects of duration of DM and antidiabetes interventions on NHL risk.