Growing global temperatures may be playing a part in the rising numbers of people developing type 2 diabetes, suggests new research from the Leiden University Medical Center and the Delft University of Technology, the Netherlands.

The prevalence of type 2 diabetes is increasing rapidly worldwide.

In 2015, 415 million adults globally were suffering from diabetes, and expectations are that the prevalence will rise by almost 55%, up to 642 million cases by 2040. In high-income countries, 91% of adults affected by diabetes have type 2 diabetes.

Interestingly, it was recently shown that acclimatization of patients with type 2 diabetes to moderate cold for only 10 days already improves insulin sensitivity. Physiologically, cold exposure activates brown adipose tissue (BAT) that has been identified to combust large amounts of lipids to generate heat.

Previously, it has been shown that BAT activity is negatively associated with outdoor temperature.

A research team headed by Leiden University Medical Center Professor Patrick Rensen set out to investigate if global increases in temperature were contributing to the current type 2 diabetes growth by negatively impacting on glucose metabolism via a reduction in BAT activity.

“In the present study, we aimed to assess the association between outdoor temperature and glucose metabolism on a countrywide as well as a global scale,” Prof. Rensen and co-authors said.

“We specifically hypothesized that diabetes incidence and prevalence of glucose intolerance increase with rising outdoor temperatures.”

The researchers used data on diabetes incidence amongst adults in 50 US states 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).

Data was also analyzed from the WHO’s Global Health Observatory online data repository system on country-wise prevalence rates of raised fasting blood glucose and obesity in 190 countries. In addition, country-wise average annual temperature data was obtained via the Climatic Research Unit at the University of East Anglia in the UK.

The team found that on average, per 1 degree Celsius increase in temperature, age-adjusted diabetes incidence increased by 0.314 per 1,000.

“We demonstrated that, on average, per 1 degree Celsius increase in temperature, age-adjusted diabetes incidence increased with 0.314 per 1,000,” the authors said.

“Similarly, the worldwide prevalence of glucose intolerance increased by 0.170% per 1 degree Celsius rise in temperature. These associations persisted after adjustment for obesity.”

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

Using their findings, the scientists calculated that a 1 degree Celsius rise in environmental temperature could account for more than 100,000 new diabetes cases per year in the United States alone, given a population of nearly 322 million people in 2015.

“The findings emphasize 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 United States last year,” the researchers concluded.

A report on the research is published online in the journal BMJ Open Diabetes Research & Care.

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Lisanne L. Blauw et al. 2017. Diabetes incidence and glucose intolerance prevalence increase with higher outdoor temperature. BMJ Open Diabetes Research and Care 5 (1): e000317; doi: 10.1136/bmjdrc-2016-000317