Rising temperatures appear to significantly increase the short-term risk for hypoglycemia among adults with type 1 diabetes (T1D), new research suggested.

An analysis of more than 32 million continuous glucose monitor (CGM) readings from nearly 700 adults with T1D in the UK showed a 26% greater risk for hypoglycemia at a temperature of 25 °C (77 °F) than at 13 °C (55.4 °F). Hypoglycemia was defined as a glucose level < 3.9 mmol/L (70 mg/dL).

The findings were published in the August 2026 issue of Diabetes Care by a team led by Harriet E. Daultrey, MBBS, PhD, of the Department of Global Health and Infection at Brighton and Sussex Medical School in Brighton and the Environment & Health Modelling Lab at the London School of Hygiene and Tropical Medicine in London, both in England.

“Our findings provide robust, individual-level evidence to support clinically guided insulin adjustments during periods of elevated ambient temperature, particularly > 25 °C,” Daultrey and colleagues wrote.

“These results also suggest ambient temperature may be considered a variable within hybrid closed-loop insulin-delivery algorithms and included in structured education, especially during increasingly frequent severe-weather warnings. They also highlight the importance of preparing clinical teams and healthcare systems to manage the increased risk of hypoglycemia during hotter weather.”

Potential mechanisms linking heat exposure to hypoglycemia include changes in insulin absorption and action, the authors noted.

Millions of CGM Readings Analyzed

The study included 679 individuals with T1D and 32,966,282 CGM readings collected between February 23, 2017, and August 8, 2024. Participants had a mean age of 46.4 years and a mean T1D duration of 23.7 years.

The researchers used a case time series design to assess the longitudinal association between ambient temperature and hypoglycemia. The model controlled for factors that remained constant or changed slowly over time, such as socioeconomic status and BMI.

The mean daily temperature during the study period was 12.0 °C (53.6 °F), with temperatures ranging from -3.7 °C to 28.7 °C. The mean daily glucose level was 10.1 mmol/L (182 mg/dL).

Peak Risk: Summer and Mondays

The researchers observed strong seasonal patterns, with lower odds of hypoglycemia in late winter and early spring, followed by a peak during the summer.

The lowest risk occurred on Mondays. The odds then increased over the course of the week and peaked toward the weekend, with a significant odds ratio of 1.14 on Saturdays compared with Mondays.

Increases in hypoglycemia were observed during both hot and cold weather, but the association was stronger for heat. The net odds ratio was 1.26 at 25 °C compared with 13 °C.

The effect was immediate, with an odds ratio of 1.10 for same-day exposure to 25 °C compared with 13 °C. Risk returned to baseline after 7 days.

Secondary analyses, including those using the continuous daily mean of CGM readings and a lower hypoglycemia threshold, confirmed the same patterns.

“These findings are particularly relevant for people with T1D who are already at higher risk of hypoglycemia, such as those with glycemia levels close to target, with a lower HbA1c or with impaired hypoglycemia awareness,” Daultrey and colleagues wrote.

“For individuals using multiple daily injections, proactive reduction in basal insulin may be required in anticipation of forecasted temperature increases to minimize hypoglycemia.”

Development of the data-linkage procedures, study design, and statistical methods applied in this study was supported by the Wellcome Trust and the Medical Research Council-UK. Daultrey reported no additional disclosures. 

Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape, with other work appearing in The Washington Post, NPR’s Shots blog, and diaTribe. She is on X @MiriamETucker and Bluesky @miriametucker.bsky.social.