A Harvard-led study found that Type 2 diabetes was associated with a higher risk for several types of cancer, with risk peaking less than a decade after diagnosis.
Researchers have long recognized an association between Type 2 diabetes and cancer. For example, in a 2010 report in Diabetes Care, experts noted a connection between diabetes and an increased risk for certain cancers and stated that possible mechanisms responsible for the link included hyperinsulinemia, hyperglycemia and inflammation. However, increasing evidence of a link between Type 2 diabetes and cancer did not translate into better understanding of how the former might affect risk for the latter.
Evidence of Hyperinsulinemia’s Role
To help fill the knowledge gap, Mingyang Song, MD, ScD, Assistant Professor of Clinical Epidemiology and Nutrition at Harvard T.H. Chan School of Public Health and Assistant Professor of Medicine at Massachusetts General Hospital, and a team of researchers conducted a prospective, two-cohort study. They analyzed the records of approximately 159,000 men and women from the Nurses’ Health Study and Health Professionals Follow-Up Study. None of the individuals had diabetes or cancer at baseline.
Individuals with diabetes had a 21% increased risk of total cancer, and their risks of obesity-related and diabetes-related cancer stood at 28% and 25%, respectively, compared with individuals without diabetes. Diabetes was associated with a higher risk of breast, colorectal, endometrial, esophageal, liver, lung, pancreatic and thyroid cancers. The findings appeared in the Journal of the National Cancer Institute.
“The most striking finding is that we showed the pattern of the relationship between duration of Type 2 diabetes and cancer risk,” Dr. Song says. “What we found was that the association peaked at around six to eight years after diagnosis of Type 2 diabetes. This is also the time when insulin levels tend to peak. That indicates the high likelihood for the insulin hypothesis for the link between diabetes and cancer risk.”
Act Soon After Diabetes Diagnosis to Reduce Cancer Risk
The mechanism driving the connection between Type 2 diabetes and cancer risk remains unclear, but Dr. Song says the most compelling hypothesis is that most patients have high insulin levels in the years immediately following diagnosis. That could promote cell proliferation.
“[These data indicate] that the best time to prevent cancer is probably in the early phase of Type 2 diabetes diagnosis,” Dr. Song says. “[W]e may consider telling some [newly diagnosed] patients to reduce [their] cancer risk.”