Association between glycosylated hemoglobin and cancer risk: a New Zealand linkage study

Background: The purpose of this study was to examine the relationship between glycosylated hemoglobin (HbA1c) level and subsequent cancer risk. Material and methods: HbA1c measurements were made on blood samples of participants in a hepatitis B (HB) screening program (1999–2001). Cancer incidence was determined by linkage to cancer registrations and hospitalization records to the end of 2004. Participants previously diagnosed with diabetes or cancer were excluded. Hazard ratios (HR) and 95% confidence intervals (CIs) were estimated using Cox regression. Results: Among the 46 575 participants (70% M aori, 12% Pacific, 5% Asian and 12% Other), 634 cancer cases were observed. For all cancers combined, a significant increased risk was found in persons with moderately elevated HbA1c levels (6%–6.9%) (HR 1.40, 95% CI: 1.11–1.76), with a smaller increased risk in persons with highly elevated levels (‡7%) (HR 1.09, 95% CI: 0.80–1.48) as compared with persons having low HbA1c levels (<6%). The HRs for respiratory cancers were 2.27 (95% CI: 1.34–3.86) for the moderate HbA1c category and 1.58 (95% CI: 0.77–3.26) for the upper HbA1c category. For endometrial cancers, the HRs were 4.05 (95% CI: 1.10–14.88) and 5.07 (95% CI: 1.20–21.31), respectively. For other cancer sites, no significantly increased risks were found. Conclusions: These findings are consistent with other evidence that abnormal glucose metabolism may be associated with an increased risk of some cancers.