Insulin doesn't appear to increase cancer or cardiovascular risk

Using basal insulin to normalize glucose levels in patients with early diabetes and pre-diabetes doesn't affect cardiovascular event or cancer rates, a study found.

The trial randomized more than 12,000 people with a mean age of 63.5 years who had cardiovascular risk factors plus impaired fasting glucose, impaired glucose tolerance or type 2 diabetes to receive daily basal insulin glargine or standard care, defined as treatment based on local guidelines or the investigator's best judgment. Insulin was titrated to a target fasting blood glucose level of ≤95 mg/dL in the glargine treatment group; in the standard care group, only 11% were treated with insulin, with a majority of patients (60%) being treated with metformin, and 19% not receiving any glucose-lowering agents. Median length of follow-up was 6.2 years. The study was presented at the American Diabetes Association annual meeting and published online by the New England Journal of Medicine on June 11.

The insulin and control groups had similar rates of myocardial infarction, stroke or death from cardiovascular causes (2.94 with insulin vs. 2.85 without per 100 person-years) and of a combined outcome of those events plus revascularization or hospitalization for heart failure (5.52 vs. 5.28 per 100 person-years). The incidence of new diabetes in the pre-diabetic patients, measured about three months after insulin was discontinued, was lower in the insulin group (30% vs. 35%; odds ratio, 0.80; P=0.05). However, insulin was associated with more weight gain (1.6 kg vs. −0.5 kg) and severe hypoglycemia (1.00 vs. 0.31 per 100 person-years). The rate of cancer did not differ between groups.

Researchers concluded that insulin glargine had a neutral effect on cardiovascular outcomes and cancer but increased hypoglycemia and weight. As the largest and longest study of its kind, this trial provides reassurance about previously suspected links between insulin and cardiovascular problems and cancer, the authors said. They attributed the extended benefit of diabetes reduction after insulin was discontinued to resting of the pancreas, although they noted that the durability of the effect is unknown.

The study also randomized patients to receive n-3 fatty acids or placebo, and results of that investigation, also published in the New England Journal of Medicine, showed no benefit or harm from the supplementation.