Heat Exposure

Extreme heat events are becoming more frequent, intense, and prolonged, increasing the risk of heat-related illness among workers performing physically demanding work in hot environments. Current occupational heat-stress guidelines aim to limit excessive increases in core body temperature and physiological strain through the use of work-rest schedules. However, these guidelines do not provide clear direction on the safe, maximum duration of continuous work that can be performed before heat-mitigation controls should be implemented, known as the initial stay time. Recent work has generated initial stay time recommendations for young and older workers performing moderate-intensity work in the heat, but these estimates were developed under normoxic conditions. In many occupational settings, workers may be exposed to additional environmental stressors such as hypoxia, including work at altitude or in oxygen-reduced environments. Hypoxia can increase cardiovascular strain, reduce arterial oxygen saturation, and alter exercise tolerance, potentially compromising the effectiveness of heat-stress guidance developed under normal oxygen conditions. Older workers may be especially vulnerable due to age-related reductions in thermoregulatory and cardiovascular function. To date, it remains unclear whether hypoxia alters physiological strain during work in the heat or whether current initial stay time and recovery recommendations remain protective under combined heat and hypoxic stress. The primary objective of this study is to determine whether exposure to hypoxia increases physiological strain during moderate-intensity work in the heat in young and older males. Specifically, investigators will assess whether normoxia-derived initial stay times and recovery recommendations for work at 29°C wet-bulb globe (37.5°C, 35% RH) temperature remain effective when workers are exposed to hypoxia equivalent to 14% inspired oxygen (simulating \~3000 m in altitude). Healthy young and older males will complete simulated occupational heat exposure under two conditions: heat alone and combined heat plus hypoxia. Participants will perform moderate-intensity treadmill work based on age-specific initial stay times, followed by prescribed work-rest cycles and seated recovery. Measures of core temperature, cardiovascular strain, oxygen saturation, skin temperature, hydration status, perceptual responses, mood, symptoms of environmental stress, and cognitive function will be assessed to determine whether hypoxia modifies responses to work in the heat. This study will provide important evidence on whether occupational heat-stress guidance requires refinement when workers are exposed to combined heat and hypoxic stress.

Extreme heat events are becoming more frequent, intense, and prolonged, increasing the risk of heat-related illness among workers exposed to hot environments. Current occupational heat-stress guidelines are designed to limit excessive increases in core body temperature and physiological strain during work in the heat through the use of work-rest schedules. However, these guidelines are largely based on single-day heat exposures and assume that workers recover in cool indoor environments between shifts. During heat events, many workers may instead recover in homes or accommodations that remain overheated, particularly in the absence of air conditioning. Inadequate overnight cooling may impair the body's ability to dissipate heat, increase physiological strain, and reduce tolerance to heat exposure on subsequent workdays. Older adults may be especially vulnerable due to age-related impairments in heat-loss capacity. To date, the effects of recovering in an overheated indoor environment on physiological strain and thermoregulatory function during repeated occupational heat exposure remain poorly understood, limiting the development of evidence-based recommendations to protect workers during prolonged heat events. The primary objective of this study is to determine whether overnight recovery in an overheated indoor environment increases physiological strain during repeated occupational heat exposure in older adults. Specifically, investigators will assess whether recovery at the recently proposed upper indoor temperature limit of 26°C and 45% relative humidity (RH) (PMID: 38329752) is sufficient to attenuate elevations in core temperature during subsequent work in the heat compared with recovery in an overheated indoor environment (31°C, 45% RH) representative of conditions commonly experienced during extreme heat events. Healthy older adults will complete two consecutive days and nights of simulated moderate-intensity occupational heat exposure, with overnight recovery occurring in either the 26°C or 31°C condition. Measures of core temperature, cardiovascular strain, heat-loss capacity, hydration status, sleep quality, cognitive function, mood, and perceptual responses will be assessed to determine the impact of overnight recovery conditions on responses to repeated heat exposure. Whole-body heat-loss capacity will also be evaluated before and after the exposure protocol as assessed during incremental, intermittent exercise protocol performed in an air calorimeter.

The goal of this clinical trial is to learn whether creatine supplementation changes how the body adapts to repeated exercise in the heat in healthy recreationally active adults and varsity athletes. The study will also examine whether creatine affects fluid balance, blood volume changes and exercise performance. The main questions it aims to answer are: Does creatine supplementation increase plasma volume and total body water during repeated heat exposure more than placebo? Does creatine supplementation improve exercise performance after heat acclimation more than placebo? Does creatine supplementation influence cardiovascular responses to heat stress? Researchers will compare a creatine supplementation group to a placebo group to determine whether creatine changes the magnitude of heat acclimation adaptations. Participants will: Complete baseline measurements of body composition, hydration, blood markers, and exercise performance. Consume either creatine monohydrate or a placebo supplement daily Complete repeated supervised exercise sessions in a controlled heated environment Undergo repeated assessments of body water, temperature, heart rate, and exercise performance throughout the study

Insulin resistance and hyperglycemia predispose individuals with type 2 diabetes mellitus (T2DM) to endothelial dysfunction and a greater risk of cardiovascular diseases (CVD). Increased CVD risk in individuals with T2DM persists despite optimal pharmacological therapy, highlighting the need to identify complementary lifestyle interventions that improve cardiometabolic functions in this population. Evidence from animal models suggests that heat exposure improves metabolic functions. Notably, weekly heat exposure for 16 weeks blunts hyperinsulinemia and hyperglycemia induced by a high fat diet in mice. In parallel, studies in humans have shown that heat exposure improves vascular endothelial function. Based on such findings, it has been suggested that heat therapy may represent an effective lifestyle intervention to improve cardiometabolic functions. However, only 1 study has examined the impact of a heat therapy intervention on individuals with T2DM, demonstrating that 6 weeks of heat exposure reduces fasting plasma glucose and hemoglobin A1C. No study has considered potential vascular benefits of heat therapy in individuals with T2DM. This project will investigate cardiometabolic responses to repeated heat exposure in men and women with T2DM. We will test the hypothesis that 12 weeks of heat therapy improves postprandial fatty acid handling, insulin sensitivity and endothelial function in individuals with T2DM.

The goal of this stepped wedge trial is to assess the practical effects of air conditioners on hot weather impacts among older adults. The main questions it aims to answer are: How does the presence of an air conditioning unit affect heat stress, heat strain, mental health, and healthcare utilization among older adults who did not previously have access to air conditioning? How, and in what conditioners, do older adults use air conditioning once it is installed in their home? Researchers will compare participants in arms with (A) and without (B) air conditioning units in the first summer season; this will allow them to assess the effect of air conditioners. In the second summer season, both arms will have air conditioning units, but those in the year two distribution arm (B) will receive an electricity subsidy, while those in the year one AC distribution arm (A) will not, allowing researchers to assess the effect of an electricity subsidy. Participants will be randomized to receive an air conditioner and financial support for electricity costs in either the first summer season or the second summer season of the study. * Heat stress, heat strain, mental health, and healthcare utilization will be assessed via participant survey. * Air conditioner utilization will be assessed via continuous load monitoring devices. * Indoor air temperature will be assessed via continuous data loggers.

Extreme heat events pose a significant health threat in Canada, as demonstrated by the 2021 heat wave that claimed over 600 lives in Western Canada. Most heat-related deaths occur indoors and are preventable. Primary care providers (PCPs), who serve 88% of Canadians, are uniquely positioned to identify and support at-risk individuals. Heat Smart, in alignment with Heat Alert and Response Systems (HARS), aims to bridge the gap between primary care and public health to enhance community resilience and reduce health inequities related to extreme heat events. This randomized control trial in Eastern Ontario will examine whether patients receiving tailored digital health messages from their family physician or nurse practitioner change their behaviour to protect themselves from extreme heat-related illness. The Heat Smart study will: * Assess risk: Analyze electronic medical records and patient surveys to identify vulnerable individuals. * Deliver tailored messages: Send personalized digital guidance via e-mail or text, offering heat safety advice and local resource information in English and French. * Issue early warning alerts: Notify at-risk patients of upcoming heat events, prompting action. * Evaluate impact: Use surveys and health data to measure effectiveness in reducing heat-related health impacts. Short-term outcomes include increased awareness and preparedness among patients about heat-related health risks. Long-term goals involve scaling the intervention across Canada to reduce heat-related illnesses, enhance social connectedness, and decrease healthcare utilization.

Heat acclimation is when you repeatedly exposure yourself to heat so that your body adapts and better tolerates heat. This project will determine if completing a heat acclimation maintenance period after heat acclimation is more beneficial than heat acclimating alone for exercise performance in the heat. To determine this, participants will exercise in the heat before heat acclimation, after heat acclimation, and after heat acclimation maintenance. Researchers will assess the heart's pumping capacity, blood volume, body temperature, and exercise performance to determine which approach is more effective.

The purpose of this study is to determine the effect of 5 days post-exercise hot water immersion on exercise performance at simulated altitude.

This study will consist of a parallel-groups design, with 30 healthy active female participants randomly assigned to either an experimental heat acclimation and exercise intervention, or a thermo-neutral exercise intervention control group. Interventions will be 10 days in duration, and consist of daily 60-minute exercise bouts under the appropriate environmental condition. Before and after each intervention, various tests will be conducted to establish exercise capacity under various environmental conditions, as well as underlying mechanisms of physiological adaptation induced by each intervention.