Among people with type 1 diabetes, higher insulin doses are linked to a greater long-term risk for cancer, according to a new study published in the journal JAMA Oncology.
Taking insulin is essential to blood glucose control and survival in people with type 1 diabetes, and the researchers did not imply in any way that people with diabetes should take any less insulin than is needed for optimal blood glucose control. In fact, the overall risk for cancer that was seen in the study — 2.8 new cancer cases for every 1,000 years that participants lived — is small enough to be dwarfed by the risk for long-term diabetes complications that may result from inadequate blood glucose control.
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But different dietary and overall diabetes management strategies may require different daily insulin doses — even for people with type 1 diabetes. How much insulin someone needs depends, in part, on how much carbohydrate they consume — which means that following a lower-carb diet can mean that less insulin is needed for optimal blood glucose control. Similarly, consuming foods with a lower glycemic index — meaning the carbohydrate is digested more slowly and causes less of a glucose rise — may require lower mealtime insulin doses. And, if your doctor prescribes it, taking the injectable diabetes drug Symlin (pramlintide) along with insulin can mean greatly reduced mealtime insulin doses. Any dietary or medical strategy to reduce your insulin doses should be followed only in consultation with your health care team, to reduce your risk for dangerously high or low blood glucose levels.
For the latest study, researchers looked at data from 1,303 people who were originally enrolled in a large study on diabetes control between 1983 and 1989. These participants then volunteered to take part in a follow-up study, which started in 1993 and included annual cancer history updates through 2012 — for a total of 28 years in which participants’ cancer status was recorded.
During the total study period, 93 participants (7%) developed cancer. The average age for a first-time cancer diagnosis was 50, and the average diabetes duration for a first-time cancer diagnosis was 25 years. Among participants who developed cancer during the study, 9% developed it within 10 years, 33% developed it after 11-20 years, and 58% developed it after 21-28 years.
Highest daily insulin doses linked to increased cancer risk
Several different factors were linked to the risk for developing cancer, including participants’ age, sex, and exercise habits. When the researchers adjusted for other factors linked to cancer, they found that daily insulin doses were strongly linked to the risk for developing cancer — compared with participants who had the lowest insulin doses, those with the highest doses were 4.13 times as likely to develop cancer. The risk for cancer climbed along with insulin doses throughout the range of doses — suggesting that insulin levels may play a role in the development of certain cancers.
The most commonly diagnosed form of cancer in the study was skin cancer, with 27 new cases, as noted in an article at MedPage Today. There were 15 cases of breast cancer, eight cases of cancers of the reproductive system, six cases of cancers of the digestive system, and five cases of head or neck cancers.
More research is needed, the researchers suggested, to learn more about the potential link between insulin and specific cancer types.
Want to learn more about insulin? Read “What Does Insulin Do?,” “Insulin Basics,” and “Everything You Ever Wanted to Know About Injecting Insulin.”
