By Jacqueline Howard
Now, researchers are looking at whether climate change may be related to another public health concern: type 2 diabetes.
Between 1996 and 2009, outside temperatures rose across the United States, as did the prevalence of diabetes, according to a study published in the scientific journal BMJ Open Diabetes Research & Care, this Monday.
"We were surprised by the magnitude of the effect," says Lisanne Blauw, a researcher at Leiden University Medical Center in the Netherlands and lead author of the study.
"We estimate that a 1 degree Celsius increase in ambient temperature can explain more than 100,000 new cases of diabetes per year in the United States alone," says Blauw. "Therefore, future research on the effects of global warming on health is of great importance."
However, this observational study simply reveals an association between climate and diabetes, not causality. Factors known to cause type 2 diabetes include being overweight or obese and having a family history of the disease.
"I think the general message should always be that association studies do not really imply a causal effect," says Dr. Adrián Vella, an endocrinologist who has investigated type 2 diabetes at the Mayo Clinic. Vella was not involved in the research linking climate change to diabetes.
Currently, about one in three Americans will develop type 2 diabetes, according to the US Centers for Disease Control and Prevention (CDC).
For the new study, the researchers analyzed information on the incidence of type 2 diabetes in the United States, including the territories of Guam, Puerto Rico, and the Virgin Islands, between 1996 and 2009. The information came from the Surveillance System for Factors of CDC risk
The researchers also analyzed information on average annual temperatures by state, using data from the National Centers for Environmental Information.
Another type of global information was also analyzed. For example, data on fasting blood glucose levels and obesity were collected through the World Health Organization's Global Health Observatory, whose database is online.
The researchers found that for every 1 degree Celsius increase in outside temperatures, there was about a 4% increase in the total incidence of diabetes in the United States, per year, between 1996 and 2009. A 1 degree Celsius increase is equivalent to a rise of 1.8 degrees Fahrenheit.
The global prevalence of glucose intolerance increases 0.17% for every 1 degree Celsius increase in temperature, according to the researchers.
"To the best of our knowledge, this study is the first to analyze the association of outdoor temperature with the incidence of diabetes and the prevalence of increased fasting blood glucose at the national and global level," the researchers wrote.
Although more research is necessary to determine why and how this correlation exists, the study formulates a hypothesis that speaks to how colder temperatures can activate a body fat called brown fat, or brown adipose tissue.
“The function of brown adipose tissue is to burn fat to produce heat, which is important to prevent a reduction in body temperature when exposed to cold external temperatures. Therefore, we believe that brown fat plays a key role in the mechanism underlying the association between external temperatures and diabetes, ”says Blauw. "In warmer climates, standing fat can become less activated, which could causally lead to insulin resistance and diabetes."
However, Vella says that brown fat doesn't have much of an impact on human metabolism. "In humans, brown adipose tissue maybe explains 1% or 2% of energy expenditure in cold situations, and chills explain much more, so that's an exaggeration," he says.
"I think that between 1996 and 2009 the environment has changed," adds Vella. “Many things have changed and that can change the incidence of diabetes, right? The composition of the current population changed somewhat. The calorie intake of that population probably changed. We don't know anything about physical activity ”.
In 2012, a report from the International Diabetes Federation indicated that type 2 diabetes and climate change could be interconnected.
Climate change threatens the supply of fresh food, which could negatively impact the diets of people with diabetes, according to that report. Also, deadly heat waves could weaken overall health through dehydration.
Last week, the Consortium of Medical Societies on Climate and Health released a report with a "medical alert," called "Climate change is harming our health."
The report highlights how, across the United States, climate change can lead to fatal heat waves, poorer outdoor air quality, dangerous and extreme weather events, food-related infections, water-related infections, mosquito and tick infections. , wildfires, and increased levels of depression, anxiety, and post-traumatic stress disorder in flood victims and farmers.