The analysis followed a landmark study in 2015 that showed insulin sensitivity could improve in patients with type 2 diabetes after only 10 days in a colder climate.
A recent finding that showed how body fat responds to colder temperatures caused scientists at Leiden University Medical Center in The Netherlands to ask the question: Is there a connection between global warming and rising rates of diabetes worldwide?
Certainly sedentary behavior and the infiltration of Western diets have their roles in the fact that an estimated 422 million people worldwide have diabetes, most of them type 2 disease (T2D). In the United States, the total number with diabetes is nearly 30 million, with all but about 1.25 million having T2D.
This new study, published in BMJ Open Diabetes Research and Care, builds on a 2015 study by Hanssen et al that appeared in Nature Medicine, which found that when patients with T2D adjust to a moderately cold environment for as little as 10 days, their insulin sensitivity significantly improves.
Exposure to cold temperatures activates brown adipose tissue (BAT), which are the fat stores the body uses to generate heat. Thus, the BMJ authors wrote, “It is thus conceivable that an increase flux of fatty acids toward BAT may result in a compensatory increased flux of glucose to other metabolically active tissues, explaining improved insulin sensitivity at lower temperature.”
First, the research team examined the association between the mean annual temperature in each US state and its diabetes incidence from 1996 to 2009. Diabetes rates vary greatly by state, with higher rates clustered in the South and Southwest, where temperatures are warmer. Diabetes data were collected from the CDC. The team also did a worldwide analysis based on rising rates of glucose intolerance and mean annual temperature.
The analysis showed that, on average, for every 1-degree Celsius increase in temperature, age-adjusted diabetes incidence rose 0.314%. A country-by-country analysis of glucose intolerance found an association of 0.170% for every 1-degree rise in temperature. These rates held up after an adjustment for obesity.
Notably, the study finds a link between warmer temperatures and rising rates of diabetes; it cannot say that global warming is causing the disease, however. And, the researchers note, “The role of BAT activity as an underlying pathway in the association between outdoor temperature and diabetes incidence may even be genetic in origin,” as the BAT of different populations are speculated to have evolved differently over millennia to adjust to temperature.
Still, the researchers concluded, “This association between temperature and raised fasting blood glucose cannot merely be due to international differences in age, sex, income, or obesity prevalence, as our analyses adjusted for these variables.”
Although other population factor may affect the results, “the fact that this association closely parallels our findings in the USA supports the notion that the ambient temperature affects the occurrence of glucose intolerance worldwide.”
Blauw LL, Aziz NA, Tannemaat MR, et al. Diabetes incidence and glucose intolerance prevalence increase with higher outdoor temperature. BMJ Open Diabetes Res Care. 2017;5:e000317. doi: 10.1136/bmjdrc-2016-000317