Epidemiologic, pharmacoepidemiologic and pathophysiologic evidence points consistently to an association between type 2 diabetes and cancer. This association could be explained by hyperinsulinemia induced by insulin resistance. We studied the association between fasting serum insulin (FSI) and cancer mortality in a population of non-diabetic individuals.

We followed 3117 healthy workers (50.2% women), included in the TELECOM cohort study, between 1985 and 1987; their median age was 38 years (Q1–Q3=30–50). Baseline FSI was measured by radioimmunoassay, the INSI-PR method. People with diabetes or cancer at baseline were excluded. Vital status and causes of death were available until December 2013. The association between FSI and cancer deaths was analysed by sex, using a Cox proportional hazards model with age as the time scale, adjusting for body mass index, smoking habits, alcohol consumption, occupational category and ethnic origin.

After a 28-year follow-up, 330 (10.6%) deaths were reported, among which, 150 were cancer-related (80 men, 70 women). In men, the association between FSI and death by cancer was J-shaped: compared to the average FSI of 7.1mU/L, men with 5mU/L and 12.9mU/L had respectively adjusted hazard-ratios (HR) of 1.88 (95% confidence interval, 1.00–3.56) and 2.30 (95% CI, 1.34–3.94). Among women, no significant association was found (adjusted HR, 1.03; 95% CI, 0.96–1.11) for an increase of 1mU/L in FSI.

These results strengthen the hypothesis of an independent risk of cancer death associated with extreme values of FSI, mainly the highest, among men, but not among women.