According to researchers at the McMaster University Department of Medicine in Ontario, Canada, conducting the largest and longest study of its kind, daily glargine insulin injections, begun during the early stages of type 2 diabetes, neither increased nor reduced the risk of heart attacks, strokes, cancer, or cardiovascular-related mortality.
Their Outcome Reduction with Initial Glargine Intervention (ORIGIN) study randomized more than 12,500 people at high risk for, or in the early stages of, type 2 diabetes to either one daily injection of glargine insulin or standard care (no insulin), over a median of 6.2 years. Researchers found no difference among the two groups in cardiovascular outcomes or in the development of any type of cancer, suggesting that daily insulin injections to normalize glucose levels are not harmful when taken over long periods of time. Patients given insulin maintained glucose levels in the normal range (90-94 mg/dL) throughout the duration of the study.
Regarding side effects, ORIGIN did confirm the presence of two previously known side effects of insulin -- hypoglycemia and modest weight gain. However, both were considered minor.