Recent studies have identified a higher risk of certain cancers among people with type 1 diabetes (T1D) and type 2 diabetes (T2D) compared to the general population.
In the case of T2D, those studies established a link between this increased risk with certain metabolic factors such as obesity or insulin resistance (i.e., decreased effect of insulin). While no explanation has yet been identified for T1D, some recently published studies offer new hints.
Using data from a large-scale study, researchers wanted to determine whether there is any observable relationship between the insulin dose used by 1,303 people with T1D and the incidence of cancer.
Participants were monitored through the Diabetes Control and Complications Trial (DCCT) and the Epidemiology of Diabetes Interventions and Complications (EDIC) study, two databases that have been in place since the 1980s. The main purpose of these studies was to assess the prevalence of complications over time.
More cancer cases among people with higher insulin doses
Over a 28-year follow-up period, 93 participants (7%) were diagnosed with cancer. On average, these participants were 50 years of age and had been living with T1D for 25 years at the time of the cancer diagnosis. Out of the 93 participants who were diagnosed with cancer, 61% were women and 39% were men.
While the study actually shows that women have a higher risk than men, it highlights another possible risk factor: high daily insulin doses.
Based on their average insulin dose administered daily (known as the total daily dose), participants in the study were divided into three categories:
- Low dosage: fewer than 0.5 units/kg daily
- Medium dosage: between 0.5 and 0.8 units/kg daily
- High dosage: more than 0.8 units/kg daily
For the purposes of the study, the above categories were defined based on a number of units per kilogram per day. This number is calculated by dividing a person’s total daily insulin dose by their weight (in kilograms).
For example: If a person weighs 67 kg (147 lbs) and takes the following doses in a day:
12 basal insulin units
4 units of rapid-acting insulin at breakfast
3.5 units of rapid-acting insulin at lunch
5 units of rapid-acting insulin at dinner
Their total daily dose is as follows: 12 + 4 + 3.5 + 5 = 24.5 units daily.To get their number of units/kg per day, they need to divide their total daily dose by their weight, i.e.: 24.5 ÷ 67 ≅ 0.36 units/kg daily.
The researchers then looked at the relationship between daily insulin doses and the incidence of cancer. They noted that higher insulin doses were associated with an increase in the number of cancer cases, which was significantly higher among participants who used high insulin doses compared to those who used low doses.
However, the number of participants was too small, and the number of cancer cases was proportionately too low to confirm a relationship between daily insulin doses and the incidence of cancer. For the same reasons, the particular types of cancer concerned could not be identified.
This finding is not, however, unique to people with T1D. Since insulin is a hormone that is naturally secreted by the body (except for people with T1D who need to administer it), it’s interesting to note that other studies have observed the same phenomenon among people without diabetes who had high blood insulin levels for various reasons (e.g., obesity, aging, sedentary lifestyle, insulin resistance).
According to some studies, high blood insulin levels combined with insulin resistance could promote the development or progression of cancer. Insulin is a hormone that supports the storage of nutrients and the development of cells, some of which can sometimes, unfortunately, evolve into cancer.
The chronic inflammatory process (article in French only) involved in T1D might also play a role by increasing the quantity of insulin needed. So, could this mean that the risk of cancer is associated with the degree of inflammation rather than with the insulin dose itself?
Since there are numerous risk factors (e.g., excess weight, sedentary lifestyle) and since the mechanisms involved in the development of cancer are complex, we can hardly conclude from this new study that high insulin doses increase the risk of cancer.
Can the required insulin dose be reduced?
First of all, it’s important to note that each person is different and has different insulin needs and a different risk of developing certain cancers. And some factors (such as genetic ones) cannot be changed.
If you have T1D and have concerns about your insulin doses, don’t hesitate to talk to the members of your healthcare team, who can help you to assess the situation and identify solutions.
Here are a few strategies that can help to increase the efficacy of your insulin and decrease your required dose:
- Make the most of technology. Some technologies like hybrid closed loop systems can help you to administer insulin doses that are closer to your actual needs, through the automated adjustment of certain settings and continuous glucose monitoring.
- Try to decrease hypoglycemic episodes. After correcting low blood sugar, you may very well need to take insulin to treat high blood sugar (hyperglycemia). In addition, the carbs you will eat to correct your hypoglycemia can lead to weight gain, which will decrease insulin efficacy. Continuous glucose monitors (e.g., Dexcom, FreeStyle Libre) that allow you to set alarms (before/upon hypoglycemia) are excellent tools to limit hypoglycemic episodes. Some types of insulin can also decrease the risk of hypoglycemia.
- Practise regular physical activity (article in French only).
- Improve the quality of your diet (e.g., limit processed, high-carb and high-fat foods).
- Avoid injecting insulin into lipodystrophies (video in French only).
- Find stress-reducing strategies.
- Talk to your healthcare team. There are certain medications typically used for T2D that can sometimes be combined with insulin.
To summarize, there are many factors that can impact the onset of cancer. Further studies will be needed to ascertain whether there really is a relationship between insulin doses and cancer prevalence, and to better understand the underlying mechanisms. However, this study encourages us to think about strategies for decreasing the quantity of insulin needed by people with T1D who use high doses, while not losing sight of blood sugar control objectives.
- Zhong W, Mao Y. Daily Insulin Dose and Cancer Risk Among Patients With Type 1 Diabetes. JAMA Oncol. Published online July 28, 2022. doi:10.1001/jamaoncol.2022.2960
- Carstensen, B., Read, S.H., Friis, S. et al. Cancer incidence in persons with type 1 diabetes: a five-country study of 9,000 cancers in type 1 diabetic individuals. Diabetologia 59, 980–988 (2016). https://doi.org/10.1007/s00125-016-3884-9
- Major JM, Laughlin GA, Kritz-Silverstein D, Wingard DL, Barrett-Connor E. Insulin-Like Growth Factor-I and Cancer Mortality in Older Men. J Clin Endocrinol Metab. 2010 Jan 15.
- Roddam AW, Allen NE, Appleby P, Key TJ, Ferrucci L, Carter HB, Metter EJ, Chen C, Weiss NS, Fitzpatrick A, Hsing AW, Lacey JV Jr, Helzlsouer K, Rinaldi S, Riboli E, Kaaks R, Janssen JA, Wildhagen MF, Schröder FH, Platz EA, Pollak M, Giovannucci E, Schaefer C, Quesenberry CP Jr, Vogelman JH, Severi G, English DR, Giles GG, Stattin P, Hallmans G, Johansson M, Chan JM, Gann P, Oliver SE, Holly JM, Donovan J, Meyer F, Bairati I, Galan P. Insulin-like growth factors, their binding proteins, and prostate cancer risk:analysis of individual patient data from 12 prospective studies. Ann Intern Med. 2008 Oct 7;149(7):461-71, W83-8.
- Godsland, Ian F. “Insulin resistance and hyperinsulinaemia in the development and progression of cancer.” Clinical science (London, England : 1979) vol. 118,5 315-32. 23 Nov. 2009, doi:10.1042/CS20090399
Written by: Sarah Haag RN. BSc.
- Maha Lebbar, MD, Msc candidate
- Amélie Roy-Fleming Dt.P., EAD, M.Sc.
- Rémi Rabasa-Lhoret, MD, PhD
- Anne-Sophie Brazeau RD, PhD
- Sonia Fontaine, Jacques Pelletier, Marie-Christine Payette, Michel Dostie, Eve Poirier, Claude Laforest, patient-partners of the BETTER project
Linguistic revision by: Marie-Christine Payette