Impact of daily incremental change in environmental temperature on beta cell function and the risk of gestational diabetes in pregnant women

Aims/hypothesis The prevalence of gestational diabetes (GDM) is higher in summer months, possibly reflecting an association between ambient temperature and blood glucose levels. However, the specific exposure and mechanism by which temperature may affect glucose metabolism in pregnancy remains unclear. We systematically evaluated the relationships of environmental temperature and changes therein over varying durations of exposure time with beta cell function, insulin sensitivity and glucose tolerance in women undergoing antepartum screening for GDM. Methods At a mean gestation of 29 weeks, 1464 women in Toronto (ON, Canada) underwent an OGTT, from which 318 were diagnosed with GDM. Blood glucose, beta cell function and insulin sensitivity were evaluated in relation to 18 temperature variables: mean temperature and change in temperature on the day of the OGTT and over the preceding 7, 14, 21, 28, 35, 42, 49 and 56 days, respectively. Results Temperature changes in the preceding 14, 21, 28, 35, 42, 49 and 56 days (rather than mean temperatures) emerged as independent predictors of blood glucose. These relationships were evident in months where mean daily temperature was rising (February – July), but not in those where it was falling (August – January). Indeed, in February – July, the temperature changes in the preceding 21, 28 and 35 days emerged as predictors of both poorer beta cell function and higher blood glucose. Moreover, in February – July, the changes in temperature in the preceding 21 days (OR 1.16, 95% CI 1.01, 1.33) and 28 days (OR 1.20, 95% CI 1.03, 1.39) were independent predictors of GDM, while mean temperatures were not. Conclusions/interpretation In pregnant women, rising environmental temperature in the 3–4 weeks prior to glucose tolerance testing may be associated with beta cell dysfunction and an increased risk of GDM.