Purpose: Some studies have suggested an increased risk of breast cancer associated with elevated fasting serum glucose in nondiabetic subjects. Given how common both breast cancer and impaired glucose tolerance are in our aging societies, this is an important issue for public health.
Methods: We performed a systematic review of prospective cohort studies that examined the association between elevated serum glucose levels in nondiabetic subjects (levels below 7.0 mml/L) and the subsequent risk of breast cancer. We performed a systematic literature search and extracted relevant data in a standard way. We then computed summary relative risks (SRR) and 95 % confidence intervals using a random effects model applied on the risk of highest versus lowest quantile of serum glucose concentrations.
Results: Ten cohort studies were retrieved. The SRR for all studies was 1.11 (1.00-1.23), with no evidence of heterogeneity or publication bias. The SRR was not affected when the analysis was restricted to the 8 studies that reported results for fasting subjects (SRR = 1.11; 95 % CI 0.98-1.25). Three studies provided BMI-unadjusted and BMI-adjusted SRRs of 1.24 (95 % CI 0.60-2.56) and 1.20 (95 % CI 0.63-2.27), respectively. Similar magnitudes of associations were observed in sensitivity analyses, but statistical significance was lost.
Conclusion: In nondiabetic subjects, the risk of breast cancer associated with fasting serum glucose levels seems to be small. Potential limitations to this meta-analysis include the fact that not all studies reported risks adjusted for adiposity and that serum glucose levels of comparison groups were variable across studies.