'Get outside and embrace the cold:' Gestational diabetes linked to warmer temperatures

Canadian researchers have uncovered a direct link between risk of gestational diabetes and what may at first seem like an unlikely source: outdoor air temperatures.

In Monday's issue of the Canadian Medical Association Journal, researchers report the relationship they found after checking records of nearly 400,000 pregnant women in the Greater Toronto Area who gave birth between 2002 and 2014.

"This is the first population study showing this relationship between air temperature and gestational diabetes risk,"said lead author Dr. Gillian Booth, a scientist at St. Michael's Hospital and the Institute for Clinical Evaluative Sciences.

Alicia Dubay's gestational diabetes illustrates the stakes for women at high risk of developing the condition. Left untreated, the temporary form of diabetes in pregnancy can result in stillbirth, increase the risk of having a difficult delivery and increase the risk of developing Type 2 diabetes for mom and baby.

"I remember after I got my diagnosis, I called my husband crying really, really hard, because I was nervous and worried about it what it meant for me and for my baby,"Dubay, 32, recalled.

Women typically take a glucose drink test 24 to 28 weeks into their pregnancy to see if their blood sugar levels are high.

Dubay's baby girl, Seraphina Rose,was born healthy and full term at 37 weeks in December 2015. A short stay in the neonatal ICU to check that the infantwas fine at regulating her blood sugars was the only effect related to the Brampton, Ont., mom's gestational diabetes.

"There were a few things that were really challenging,"Dubaysaid. "Just keeping on top of all the scheduling of everything that you need to do" to manage the condition while working full time. It included:

• Carefully planned and prepared meals and snacks.
• Blood glucose checks four times a day.
• Weekly ultrasounds.
• More regular medical appointments to keep on top of potential complications.

"With gestational diabetes, you've got this disease but you've also got this child growing inside of you that needs nourishment and very specific kinds of food."

The whole process was "difficult but doable" and definitely worth it, she said.

The adaptations and their vital consequencesaddto the appeal of potential simple new way of reducing the risk of gestational diabetes.

Booth's teamtook advantage of the wide fluctuations of temperatures Canada hasbetween seasons to explore a natural experiment.

Cooler temperatures, brown fat

It was based on the emerging science of how brown fat in humans becomes active in cold to generate heat and metabolism throughout our bodies.

• Turn down thermostat for weight loss, scientists propose

For instance, when previous investigators lowered the thermostat from 24 C to 19 C, nuclear PET scans on humans showed substantial improvements in insulin sensitivity.

Even a small increase in the air temperature might actually mean that many more women are going to have gestational diabetes.- Dr. Gillian Booth

Those experiments can't be done on pregnant women.

Instead, Booth's team checked the Ontario Diabetes Database for gestational cases and historical weather data to calculate a 30-day average of high and low air temperaturesbefore the pregnant women were screened with a glucose drink test.

When women are in their second trimester of pregnancy, they become less sensitive to the hormone insulinand the sensitivity ramps up in the third trimester, Booth said. The hormone insulin is made by the pancreas, allowing the body to properly use sugar from carbohydrates in food.

The researchers found that after adjusting for age, number of pregnancies, initial body mass index and socioeconomic factors, each 10 C increase in average air temperature was associated with a six per cent to nine per cent greater likelihood of having gestational diabetes.

"If you were at high risk, this actually could be something that could push you over the edge," Booth said.

Each year, an estimated 15 million pregnancies worldwide are affected by gestational diabetes.

The study's authors said that if the association between air temperature and risk of gestational diabetes is real, then lowering home thermostats and spending more time outdoors in cool weather may reduce the risk of gestational diabetes.

They also note that climate change models forecast a rise of 1 to 2 C in surface temperatures by 2050.

"Even a small increase in the air temperature might actually mean that many more women are going to have gestational diabetes," Booth said.

Since the study was not a randomized control trial, cause-and-effect can't be determined.

Booth acknowledged the researchers weren't able to account for other important behaviours that affect gestational diabetes risk, such as what the women ate or how much physical activity they did.

When possible, get outside

Overall, the study was well designed and rigorously carried out, said Dr. Jan Hux, chief science officer at Diabetes Canada. She was not involved in the research.

At an individual level for women at low risk, the findings may not necessarily have an impact, Hux said.

"Every 10 degree increase in ambient temperature increases the risk of gestational diabetes by about eight per cent, but every five-year age increase increases risk by 70 per cent and being of a high-risk ethnicity doubles the risk," Hux said.

For women like Dubay who are already at high risk for gestational diabetes, staying cool can help reduce that risk.

"For some,this may be more difficult as women in poverty may not have easy access to air conditioning," Hux said."When possible, get outside and embrace the cold."

Dubay said she walked in the cold during her pregnancy but it wasn't enough to overcome the hormonal conflict she faced between her placenta and pancreas. She'll keep the lower thermostat idea in mind if she and her husband decide to try for another pregnancy.

The study was funded bythe St. Michael's Hospital Foundation and the Canadian Institutes of Health Research.