Climate change may play a part in rising diabetes numbers, a new study reports. Based on population data from 2015, the researchers estimate that a 1°C increase in outdoor temperature contributes to more than 100,000 new cases of diabetes each year in the United States alone.

The intention of the team of Dutch researchers from the Leiden University Medical Center was to investigate the association of outdoor temperature with diabetes incidence and prevalence of glucose intolerance, on a countrywide and global scale. The researchers used data on diabetes incidence among adults in 50 states of the USA and three territories (Guam, Puerto Rico and Virgin Islands) for the years 1996 to 2009 from the National Diabetes Surveillance System of the Centers for Disease Control and Prevention (CDC).

The team wanted to know if global increases in temperature were contributing to the current type 2 diabetes growth by negatively impacting on glucose metabolism via a reduction in brown adipose tissue (BAT) activity.

Global Warming And Insulin Sensitivity

Brown adipose tissue’s function in the body is to transfer energy from food into heat. Previous studies have shown that exposure to cold stimulates BAT, thus leading to modest weight loss and improved insulin action and sensitivity - making a person less likely to develop diabetes.

Worldwide, the prevalence of type 2 diabetes is increasing rapidly. In 2015, 415 million adults globally had the condition and it is expected that prevalence will rise by almost 55% - up to 642 million cases by 2040.

Researchers found that on average, per 1°C rise in temperature, age-adjusted diabetes incidence increased by 0.314 per 1,000.

Similarly, the worldwide prevalence of glucose intolerance increased by 0.17% per 1°C rise in temperature. These associations were the same after obesity was taken into account.

Such findings indicated that the diabetes incidence rate in the USA and prevalence of glucose intolerance worldwide did increase with higher outdoor temperature.

Observational Study

This was an observational study, so no firm conclusions can be drawn about cause and effect, but the authors analyzed longitudinal state-level data for each state separately before pooling the results. They also found that once they had taken into account important inter-country differences, such as age, sex, income and obesity, this did not materially change the results on the global level.

The study was not able to assess the directness of an association between body mass index (BMI) and diabetes incidence or prevalence in its models because continuous data on BMI were not available.

The authors conclude:

“These findings emphasise the importance of future research into the effects of environmental temperature on glucose metabolism and the onset of diabetes, especially in view of the global rise in temperatures with a new record set for the warmest winter in the USA last year."

The work was supported by a grant from the Board of Directors of the Leiden University Medical Center, and a grant from the Netherlands Organization of Scientific Research.

Blauw LL, Aziz NA, Tannemaat MR, et al Diabetes incidence and glucose intolerance prevalence increase with higher outdoor temperature BMJ Open Diabetes Research and Care 2017;5:e000317. doi: 10.1136/bmjdrc-2016-000317

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