Relationship between HbA1c and cancer in people with or without diabetes: a systematic review

To identify the relationship between HbA1c and cancers in people with or without diabetes.

Cancer is a major public health problem, accounting for 8.2 million deaths worldwide in 2012. HbA1c level has been associated with the risk of developing certain cancers, although the existing evidence is conflicting.

EMBASE, MEDLINE, CINAHL and the Cochrane Library were searched. Eligible articles included randomized controlled trials, cohort studies, case-control studies, systematic reviews and meta-analyses. Participants of either sex, with or without Type 1 or 2 diabetes, were included. The studies were assessed using the Scottish Intercollegiate Guidelines Network (SIGN) criteria by two independent assessors. No meta-analysis was performed because of the heterogeneity of results.

A total of 19 studies from 1006 met the inclusion criteria, of which 14 were cohort studies and five were nested case-control studies. Eight studies investigated outcomes for all cancer sites. Four of these studies reported that higher HbA1c levels were associated with higher incidence and/or mortality risk for all cancers. One study observed a U-shaped relationship between HbA1c and cancer incidence and mortality. Increasing HbA1c levels were associated with increasing risk of developing colorectal, pancreatic, respiratory and female genital tract cancers. No increased risk was observed for breast cancer, gastrointestinal or urological malignancies.

HbA1c appears to be associated with cancer incidence and/or cancer mortality, but further studies are needed to fully understand the complex relationship between HbA1c and cancer.