Study: Higher Insulin Doses May Increase Cancer Risks in Type 1 Diabetes

A new analysis has suggested that people with type 1 diabetes that use larger amounts of insulin have an increased risk of cancer.

The news arrived in the form of a research letter published by JAMA Oncology, written by Wenjun Zhong, PhD, a statistician with pharmaceutical giant Merck, and Yuanjie Mao, MD, PhD, a professor of endocrinology at Ohio University.

Zhong and Mao were working with an old and important data set: the Diabetes Control and Complications Trial (DCCT) and the Epidemiology of Diabetes Interventions and Complications (EDIC) study. These two trials were the first to definitively link intensive glucose control with reduced risk of diabetic complications, changing mainstream diabetes treatment as we know it. The DCCT and EDIC remain the best looks we’ve ever had at long-term outcomes in type 1 diabetes, and continue to yield fresh insights.

Study participants were stratified into low, medium, and insulin high insulin use categories:

Low use: <0.5 units per kilogram per day (38.5 units per day for an average American woman weighing 170 pounds)
Medium use: Between 0.5 and 0.8 units/kg per day
High use: >0.8 units/kg per day (61.6 units per day for an average American woman)

Those in the high use category were nearly 50% more likely to develop cancer than those in the low use category, with the medium use category nearly as high.

It is unclear from the analysis if the increased use of insulin itself causes cancer, or if the increased use of insulin is simply a consequence of other health problems that might be associated with cancer development. High levels of endogenous insulin have been linked with cancer in people without diabetes, as has insulin resistance, two conditions so related that it is difficult to tease them apart.

It took decades for the increased risk of cancer to reveal itself among the participans in the DCCT and EDIC trials. Most of the cases of cancer identified in the new analysis were diagnosed in the third decade of follow-up, 20 years or more after the trials began. The average patient was 50 years old at the time of their first cancer diagnosis.

Other factors, including glucose control and obesity, did not have a correlation with cancer incidence.

What does it mean for real people with type 1 diabetes? Dr. Mao interpreted the results:

Our results implied that clinicians might need to balance the potential cancer risk when treating patients with type 1 diabetes on a high daily insulin dose or that improving insulin sensitivity may be preferred than simply increasing the insulin dose.

It seems unlikely that doctors will recommend that patients intentionally take less insulin to reduce the risk of cancer, given the overwhelmingly negative effect of chronic hyperglycemia. Optimal glycemic control remains paramount for people living with type 1 diabetes.

But it is possible to reduce insulin requirements the right way: by improving your insulin sensitivity. Insulin sensitivity is a blend of both modifiable and unmodifiable factors (like age and family history). According to the CDC, the two biggest modifiable factors are excess weight and physical activity. Working out regularly and losing weight should reduce the amount of insulin you need to stay comfortably in your blood sugar range. There are other smaller factors too, including sleep quality and nutrition. Check out our article: “How to Become More Insulin Sensitive.”

Exercise and diet can also reduce short-term insulin requirements. A lower-carbohydrate diet, especially one that avoids sugar and simple starches, can reduce insulin requirements as quickly as your next meal. And many people with diabetes find that cardiovascular exercise, even at a light intensity, is a better way of correcting some blood sugar highs.

While the news gives us another reason to consider prioritizing insulin sensitivity, you should speak to your doctor before making any dramatic diet or lifestyle shifts. A rapid drop in insulin requirements carries with it a risk of hypoglycemia, and it may be necessary to quickly change your dosage of insulin and other glucose-lowering medications.


For people with type 1 diabetes, high daily insulin usage may be associated with increased long-term risk of cancer.

The change in absolute risk is not massive, and it shouldn’t be any reason for panic. However, it is yet another reminder of the value in reducing insulin requirements through diet, exercise, and other healthy lifestyle habits. When your body is more insulin sensitive, it’s easier to keep your blood sugar in range, and there may be long-term benefits, to boot.

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