Common belief that insulin puts diabetics at risk of heart disease may not be true

By: Bernard Ho

In patients experiencing diabetes mellitus, the body is either unable to produce insulin or is resistant to the body’s own insulin. The usual treatment for this ailment is exercise and dietary modifications, but when the disease becomes more severe, exogenous insulin injections must be given on a consistent basis in order to regulate blood sugar levels. However, past observational studies have shown that higher insulin levels are associated with an increased risk of cardiovascular disease. Thus, insulin injections to treat diabetes may lead to problems elsewhere in the body.

Recently, researchers at McMaster University put this belief to the test. Dr. Hertzel Gerstein, a professor at McMaster’s DeGroote School of Medicine and deputy director of the Population Health Research Institute, conducted a randomized control trial along with several other researchers to determine whether exogenous insulin increases the risk of cardiovascular disease. In the study, over 12,500 people from 40 countries, who were at high risk for or were in the early stages of Type II diabetes, were randomized to either one daily injection of insulin or no insulin for an average of six years. After analyzing the data, researchers found no difference amongst the two groups in cardiovascular outcomes.

“People have been debating the question of whether there are adverse consequences to long-term insulin use for years,” said Gerstein. “This study provides the clearest answer yet to that question: no, there are not.” Indeed, the hazard ratio for heart disease between the treatment groups was 1.02, meaning that those who were given insulin experienced cardiovascular outcomes at almost the same rate as those who were not. Moreover, the participants of the study given insulin maintained normal fasting blood sugar levels, below 6 mmol/L.

A second key finding discovered by the researchers was that those who do not yet have diabetes, but are at a high risk of developing the illness and who receive daily insulin injections, have a 28% lower chance of developing the disease, even after the injections are stopped. This suggests that some people who start insulin injections won’t necessarily be looking at treatment for the rest of their lives. The study also confirmed the presence of two previously known side effects of exogenous insulin – hypoglycemia (low blood sugar) and modest weight gain. Both were considered to be minor from a medical perspective, with participants experiencing a small risk of hypoglycemia and gaining an average of 3.5 pounds during the study.

This study was part of a larger study known as the ORIGIN (Outcome Reduction with Initial Glargine Intervention) Trial, led by Dr. Gerstein and Dr. Salim Yusuf, that also looked at the effects of omega-3 fatty acids on cardiovascular diseases. The ORIGIN Trial has since been completed and the results have been published in the New England Journal of Medicine.