The goal of this clinical trial is to learn how different temperatures affect blood sugar levels in adults with type 1 diabetes. Climate change is causing more extreme hot and cold weather, and people with type 1 diabetes may be at higher risk during these temperature changes. The main questions it aims to answer are: * Do different temperatures (cold, normal, or hot) change blood sugar levels in people with type 1 diabetes? * How does temperature affect insulin absorption in the body? Researchers will compare three different temperature conditions to see how each affects blood sugar levels and insulin in the body. Participants will: * Complete a screening visit with body measurements and questionnaires * Attend 3 separate study visits, each in a different temperature setting: * Cold room (10°C/50°F) * Normal room temperature (23°C/73°F) * Hot and humid room (36°C/97°F with 65% humidity) * Sit for 2 hours in each temperature condition while researchers monitor their blood sugar, heart rate, and body temperature * Wear a continuous glucose monitor for 48-72 hours before each visit * Keep a diary of food, sleep, and activity for 24 hours before and after each visit Each temperature visit is separated by at least 3 days. The study helps researchers understand if people with type 1 diabetes need special guidance for managing their blood sugar during extreme weather.
Background and Rationale Climate change is increasing the frequency of extreme weather events, including heat waves and cold snaps. People with type 1 diabetes face higher risks of illness and death during these extreme temperature periods compared to people without diabetes. However, the reasons for this increased risk are not well understood. When insulin is injected under the skin, it forms a small reservoir from which it gradually enters the bloodstream. Temperature may affect how quickly this insulin is absorbed. Warmer temperatures increase blood flow to the skin, which could speed up insulin absorption and potentially cause blood sugar to drop too low (hypoglycemia). Colder temperatures might slow insulin absorption, leading to higher blood sugar levels (hyperglycemia). Previous research from the 1980s showed that heating or cooling the injection site affects insulin absorption, but these studies were conducted before modern rapid-acting insulins and diabetes technologies like insulin pumps and continuous glucose monitors were available. No recent studies have examined how whole-body temperature exposure affects insulin absorption and blood sugar control in people with type 1 diabetes. Study Design Overview This is a randomized, crossover clinical trial where each participant will experience all three temperature conditions in random order. The study includes: * 1 preliminary visit for screening and measurements * 3 experimental visits (cold, neutral, hot conditions) * Total participation time: approximately 14 hours over up to 4 months Study Population The study will enroll 30 adults aged 18-45 years with type 1 diabetes for at least 2 years. Participants will be equally divided by: * Sex: 50% male, 50% female * Insulin delivery method: 10 using multiple daily injections, 10 using insulin pumps, 10 using hybrid closed-loop systems Preliminary Visit Procedures During the first visit at the Montreal Clinical Research Institute (IRCM), participants will: * Review and sign informed consent documents * Complete medical history and lifestyle questionnaires * Fill out a heat exposure questionnaire based on Health Canada guidelines * Complete the GENESIS PRAXY questionnaire to document gender-related factors * Undergo body measurements including height, weight, waist circumference, and body composition scan * Have resting heart rate and blood pressure measured * Receive training on continuous glucose monitor use (if not already using one) Experimental Visit Procedures Each of the three experimental visits will take place at Centre ÉPIC and follow the same protocol in different temperature conditions: Pre-Exposure Phase (60 minutes) * Participants arrive 2 hours after eating a standardized snack (100g Greek yogurt) with their usual insulin dose * Body weight measurement * Installation of rectal temperature probe (self-inserted privately) * Placement of intravenous catheter for blood sampling * Attachment of skin temperature sensors, blood pressure cuff, and heart rate monitor * 60-minute rest period at room temperature to establish baseline measurements Temperature Exposure Phase (120 minutes) Participants will sit in an environmental chamber set to one of three conditions: * Cold: 10°C (50°F) - causes shivering and increases energy expenditure by approximately 80% * Neutral: 23°C (73°F) - comfortable room temperature * Hot/Humid: 36°C (97°F) with 65% humidity - simulates a hot summer day in Montreal Measurements During Exposure Continuous monitoring: * Heart rate via chest strap monitor * Core body temperature via rectal probe * Skin temperature at four sites (arm, chest, thigh, calf) * Blood sugar levels via continuous glucose monitor (checked every 15 minutes) Intermittent measurements: * Blood pressure every 10 minutes * Blood samples at baseline, 60 minutes, and 120 minutes for analysis of glucose, insulin, glucagon, and other metabolic markers * Comfort and sensation ratings every 10 minutes using visual scales for thermal comfort, thermal sensation, and thirst Safety Monitoring Throughout each visit, research staff will continuously monitor participants for: * Signs of hypoglycemia (low blood sugar) - treated immediately with glucose if needed * Core body temperature limits (stopped if ≤35.5°C during cold or ≥39.5°C during heat exposure) * Blood pressure limits (stopped if \>180/110 mmHg or \<90/60 mmHg) * Participant comfort and willingness to continue Data Collection 24-Hour Activity Logs Participants will record their food intake, insulin doses, sleep patterns, and physical activity for: * 48 hours before the preliminary visit (baseline lifestyle) * 24 hours before each experimental visit * 24 hours after each experimental visit Continuous Glucose Monitoring A Dexcom G7 sensor will be installed 48-72 hours before each visit to capture: * Glucose patterns during temperature exposure * 24-hour glucose control before and after each visit * Time spent in target range (3.9-10.0 mmol/L) * Time spent above target (\>10.0 mmol/L) * Time spent below target (\<3.9 mmol/L) Laboratory Analyses Blood samples will be analyzed for: * Plasma glucose and insulin levels * Glucagon (hormone that raises blood sugar) * Free fatty acids and glycerol (markers of fat metabolism) * Other metabolic hormones Special Considerations For Female Participants Study visits will be scheduled during the follicular phase of the menstrual cycle (or placebo pill phase for those using oral contraceptives) since hormonal changes can affect blood sugar levels. Insulin Delivery Methods The study will examine whether different insulin delivery methods (injections, pumps, or automated systems) respond differently to temperature changes. Participant Safety and Comfort * At least two research staff members will be present during each visit * One staff member will remain in the environmental chamber with the participant * Participants can request to stop the exposure at any time * Emergency procedures are in place for severe blood sugar episodes * Socks and gloves will be provided during cold exposure if needed Study Significance This research will provide the first modern evidence about how environmental temperature affects insulin absorption and blood sugar control in people with type 1 diabetes. The findings could lead to new clinical guidelines for diabetes management during extreme weather events, potentially reducing the increased health risks that people with type 1 diabetes face during heat waves and cold snaps. The study results may inform recommendations for insulin dose adjustments during temperature extremes and help health care providers better advise patients with type 1 diabetes about managing their condition during increasingly frequent extreme weather events related to climate change.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
NONE
Enrollment
30
Systematic exposure to controlled temperature and humidity conditions in a specialized environmental chamber. Each exposure lasts 120 minutes with participants remaining seated throughout. All exposures include standardized pre-exposure preparation (60-minute baseline period at room temperature), continuous physiological monitoring, standardized clothing, and identical blood sampling schedules. Safety protocols include continuous staff supervision, predetermined stopping criteria for extreme body temperatures or blood pressure changes, and immediate availability of warming/cooling interventions and hypoglycemia treatment protocols.
Institut de recherches cliniques de Montréal
Montreal, Quebec, Canada
Change in plasma glucose concentration during temperature exposure
The primary outcome is the change in plasma glucose levels (mmol/L) from baseline to end of exposure across the three temperature conditions (cold 10°C, neutral 23°C, hot/humid 36°C). Blood samples will be collected via intravenous catheter and analyzed for plasma glucose concentration. This measure will assess whether ambient temperature affects blood glucose control in individuals with type 1 diabetes, with the hypothesis that cold exposure may increase glucose levels due to slower insulin absorption, while heat exposure may decrease glucose levels due to faster insulin absorption.
Time frame: Measured at baseline, 60 minutes, and 120 minutes during each 2-hour environmental chamber exposure.
Change in plasma insulin concentration during temperature exposure
Change in circulating insulin levels (pmol/L) from baseline across the three temperature conditions. Blood samples collected via intravenous catheter will be analyzed for plasma insulin concentration to assess temperature effects on insulin absorption from subcutaneous injection sites.
Time frame: Measured at baseline, 60 minutes, and 120 minutes during each 2-hour environmental chamber exposure.
24-hour time in glucose range
Percentage of time spent in target glucose range (3.9-10.0 mmol/L) as measured by continuous glucose monitoring (Dexcom G7). This will assess whether temperature exposure has lasting effects on glucose control beyond the immediate exposure period.
Time frame: 24 hours before and 24 hours after each temperature exposure visit.
24-hour time above glucose range
Percentage of time spent above target glucose range (\>10.0 mmol/L) as measured by continuous glucose monitoring. This measure will identify potential hyperglycemic episodes following temperature exposure.
Time frame: 24 hours before and 24 hours after each temperature exposure visit.
24-hour time below glucose range
Percentage of time spent below target glucose range (\<3.9 mmol/L) as measured by continuous glucose monitoring. This safety measure will identify potential hypoglycemic episodes following temperature exposure.
Time frame: 24 hours before and 24 hours after each temperature exposure visit.
Continuous glucose monitor accuracy
Mean absolute relative difference (MARD) between continuous glucose monitor readings and plasma glucose measurements. This will assess whether temperature conditions affect the accuracy of glucose monitoring technology, which is critical for diabetes management during extreme weather.
Time frame: During each 2-hour temperature exposure.
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