Researchers at the London School of Hygiene & Tropical Medicine and University College London have estimated the risk of 16 different cancers across the whole glycaemic spectrum in a population sample from the UK Biobank and UK cancer registry.
Among 378,253 individuals with median follow-up time of 7.1 years, 21,172 (5.6%) had an incident cancer diagnosis.
The cancers investigated were prostate, colorectal, lung and pre- and post-menopausal breast cancers; oesophageal, stomach, pancreatic cancer, melanoma, uterus, ovarian, kidney, bladder, central nervous system, non-Hodgkin’s lymphoma, multiple myeloma and leukaemia.
Age-standardised rates per 1000 person years (PYs) for any cancer in those with normal, prediabetic and diabetic HbA1c levels were 8.65, 10.69 and 9.89, respectively.
Age-standardised rates of prostate cancer were lower among individuals with diabetic levels of HbA1c (2.84 per 1000 PYs) than those with normal HbA1c (4.09 per 1000 PYs).
Conversely, rates of colorectal cancer were higher among individuals with diabetic levels of HbA1c (1.34 per 1000 PYs) than those with normal HbA1c (1.01 per 1000 PYs).
For lung and postmenopausal breast cancer, rates were similar between those with normal and diabetic HbA1c levels but elevated among those with prediabetic levels of HbA1c.
Similar rates of premenopausal breast cancer were observed among those with normal and diabetic levels of HbA1c but lower among those with prediabetic levels of HbA1c; however, there were only five cases in this group.
After multivariable analysis, there was no clear evidence of an association between HbA1c and incidence of prostate, colorectal and lung cancer.
There was evidence of increased risk of premenopausal breast cancer at lower levels of HbA1c (HR, 1.27; 95% CI, 1.00-1.60 for 25 vs 35 mmol/mol) and decreased risk at higher levels of HbA1c (HR, 0.71; 95%CI, 0.54-0.94 for 45 vs 35 mmol/mol; HR, 0.50; 95%CI, 0.26-0.93 for 55 vs 35 mmol/mol).
There was weak evidence of an association between lower HbA1c and increased risk of postmenopausal breast cancer (HR, 1.19; 95% CI, 0.99-1.43 for 25 vs 35 mmol/mol).