Global Warming's Insidious Effect on Diabetes

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After what seems like a never-ending stream of superstorms, droughts, floods, and wildfires, there should be little doubt that climate change is having a dramatic impact on our lives. But global warming may also be causing other, subtler impacts on our health. Earlier studies, including a blistering 2012 BMC Public Health report, found that our ever-expanding waistlines were having the unintended consequence of pushing the mercury higher, as more resources were being used to cool, nourish and transport our excess weight, a trend that scientists say contributes to climate change because increased fossil fuel requirements result in more greenhouse gas emissions.

Really, this is just simple science. Energy use is a function of the basal metabolic rate, or the amount of energy an individual consumes at rest. Big bodies need more food, which means more food must be produced, packaged, transported and refrigerated, increasing our overall electricity and fuel needs. Heavier bodies also need more fuel to move around as engines and motors strain under increased demands. Are you getting the picture?

More recently, as climate change plays havoc with the weather, an unintended but not unusual consequence of obesitydiabetes—is also on the rise. Indeed, climate change and diabetes are flipsides of the same coin, says a newly published study in the peer-reviewed journal, BMJ Open Diabetes Research & Care. This study found a corresponding increase in the number of type 2 diabetes diagnoses—more than 100,000 annually in the U.S. alone—when temperatures rise by just by just one degree Celsius or 1.6 degrees Fahrenheit.

Although the researchers couldn’t exactly determine why rising temperatures caused a spike in diabetes cases, they also noticed an increase in obesity cases wherever climate change was prevalent, buttressing those earlier studies showing a link between global warming and obesity. Obesity is a major type 2 diabetes risk factor, and the researchers also found that each 1-degree Celsius temperature increase was associated with a 0.173 percent increase in obesity prevalence. Today, roughly 30 percent of overweight people have the type 2 diabetes, and 85 percent of diabetics are overweight. About 79 million Americans, or 35 percent of people 20 or older, have pre-diabetes. While it’s certainly true that not all obese folks are diabetic, the risk increases significantly as the numbers on the scale rise.

Scientists have long predicted that even the slightest temperature increase could herald disaster, leading to rising sea levels, lower crop yields, and extinction of already vulnerable species resulting from habitat loss. We know that climate change can create favorable conditions for the spread of some lethal conditions, including water-borne diseases such as malaria and dengue fever, thanks to rising temperatures that expand disease-spreading mosquitoes’ range, as well as cholera, legionella, salmonella, and other water-borne illnesses.

Diabetes, of course, isn’t a water-borne illness. It’s not an infectious disease either. People develop type 2 diabetes when their bodies become less sensitive to insulin, the result most often of extra pounds and a sedentary lifestyle. Lowered insulin sensitivity, in turn, causes blood sugar spikes, that left untreated, can eventually lead to heart disease, nerve damage, kidney disease and other serious health issues.

In the BMJ study, Dutch researchers fingered an unusual suspect as the cause of the rise in diabetes cases—brown fat. Known also as brown adipose tissue, or BAT, this fat kicks into gear when temperatures are low and the body draws on an additional heat source (burning fat and glucose) to stay warm.

A small but highly regarded 2015 Nature Medicine study of 8 adults with type 2 diabetes found that after 10 days in moderately cold weather, the subjects’ metabolisms improved and they became more insulin sensitive, reversing a key symptom of the disease. A 2016 study found a correlation between outside temperature and a measure of long-term blood sugar called HbA1c. When temperatures rose, so did the subjects’ HbA1c.

These results led the Dutch researchers to speculate that climate change could at least partially explain the global type 2 diabetes spike. In 1908, 108 million adults had the disease; in 2016, anywhere from 371 to 400 million people worldwide had type 2 diabetes, according to the International Diabetes Federation. This number is expected to hit 622 million by 2040. Looking at information from the U.S. Centers for Disease Control and Prevention, which included the diabetes prevalence in all 50 states for each year between 1996 and 2013, as well as the average temperature for each state in each year from the National Centers for Environmental Information, the researchers found that the higher the average temperature at a particular time and place, the “higher the age-adjusted incidence of diabetes.”

Even when the researchers adjusted for the obesity prevalence in each state, they found that each 1-degree temperature increase was associated with 2.9 additional cases of diabetes per 10,000 people. Bottom line: the warmer the location, the higher the incidence of diabetes. And there was no apparent geographical pattern which could explain this association, the researchers said.

The study wasn’t designed to show the link between air temperature and diabetes, but the researchers concluded that BAT didn’t have much work to do when temperatures are already warm, and this decrease in BAT activity with increasing environmental temperature adversely affected glucose metabolism, leading to an increase in type 2 diabetes incidents.

Of course, cold exposure may not be an optimal type 2 diabetes prevention and/or treatment strategy, so scientists are looking at pharmacological strategies that mimic cold exposure’s beneficial effects, noted one of researchers in the BMJ Open study. Despite some obvious study limitations, like an inability to account for changes in body mass index (BMI), which is directed correlated with type 2 diabetes, the results point out the need for more research into the effects of environmental temperature on glucose metabolism and type 2 diabetes onset.