Could warmer temperatures raise diabetes risk in pregnancy?
Outdoor air temperature may influence a pregnant woman's risk of developing gestational diabetes, a new study suggests.
Mothers-to-be in very cold climes are less likely to develop diabetes during pregnancy than women exposed to hotter temperatures, researchers say.
If borne out in other studies, these findings could have important implications for the prevention and management of gestational diabetes, said study lead author Dr. Gillian Booth.
Changes in temperature may only lead to a small increase in the risk of gestational diabetes, but the number of women affected may be substantial, said Booth. She is a scientist at the Li Ka Shing Knowledge Institute at St. Michael's Hospital in Toronto.
Also, areas that are getting hotter because of climate change could see more cases of gestational diabetes, the study authors theorized.
Others are less certain of this link, however.
"Temperature and risk of diabetes is a hot topic," said Dr. Joel Zonszein, director of the clinical diabetes center at Montefiore Medical Center in New York City.
However, the study doesn't show a direct cause-and-effect relationship, and Zonszein cautioned that it's too soon to consider the findings definitive.
"Pregnant women or those wanting to become pregnant should not pay attention to this finding at this time, as more studies are needed to show a true causal effect," said Zonszein, who wasn't involved in the study.
Moreover, "the findings of this study do not support that climate change, a rise in global temperatures, increases the incidence of diabetes in Canada or worldwide," he said.
Booth explained that gestational diabetes in women develops in the second trimester of pregnancy and is usually temporary. Women are screened for it at 24 to 28 weeks of pregnancy.
If there is a connection between temperature and gestational diabetes risk, cells called brown fat might help explain it.
According to Zonszein, "Brown fat cells are cells that -- instead of storing energy -- burn energy."
Booth speculated that extreme cold triggers activity of brown fat, thus controlling weight gain. It might even lead to weight loss, improving blood-sugar levels, she noted.
However, Zonszein said that many environmental factors -- such as excessive food intake, sugary drinks, inactivity, stress and lack of sleep -- can cause gestational diabetes in women genetically susceptible to the disease.
"Genetic factors are very important," he said, "and they are affected by many environmental factors, probably temperature is one more."
For this study, the researchers analyzed about 500,000 births in the Toronto area over 12 years. The researchers also looked at the average temperature for 30 days before diabetes testing, then compared temperature readings with results of the diabetes testing.
In women exposed to extreme cold -- 14 degrees Fahrenheit or lower -- in the month before the test, gestational diabetes was less than 5 percent. But it was about 8 percent for women when temperatures averaged 75 degrees Fahrenheit or higher, the findings showed.
Moreover, the odds of developing gestational diabetes rose slightly with every 18-degree rise in temperature, Booth said.
The association held up whether women were born in hot climates or colder regions, she added.
"Furthermore, the same association was seen when we looked at consecutive pregnancies in the same woman," Booth said.
Besides a healthy diet and physical activity to avoid excess weight, controlling temperature might be something women can do for a healthier pregnancy, Booth suggested.
"For example, turning down the thermostat and getting outside in the winter, or using air conditioning in summer, and avoiding excess layers in hot weather may help to lower the risk of gestational diabetes," she said.
An association between temperature and gestational diabetes was also reported last September in a Swedish study. In that paper, researchers found that gestational diabetes was more common in the summer than in other seasons.
Booth said the findings of the new study might also pertain to developing type 2 diabetes.
"The risk factors for gestational diabetes and type 2 diabetes are virtually the same," she said.
The report was published online May 15 in the CMAJ (Canadian Medical Association Journal).