RecruitingNAINTERVENTIONAL

Identifying the Limits of Survivability in Heat-exposed Older Females

This study explores how older women cope with very hot conditions. With hotter summers becoming more common due to climate change, it's important to understand how extreme heat affects people, especially older women who may be at higher risk. We want to find out the specific limits of heat and humidity where the body can no longer cool itself down effectively. Participants will go through different controlled heat and humidity tests within a laboratory setting. We'll monitor their body temperature, heart, and how they feel both physically and mentally. This will help us understand when the body reaches its limits and what impact different heat levels have, ultimately aiming to improve safety guidelines during heatwaves.

At a glance

Status

Recruiting

Phase

Sponsor

University of Ottawa

Enrolment target

Start

16 Jul 2025

Estimated completion

31 Jan 2026

Heat Stress Temperature Change, Body Aging Thermoregulation Heat Exposure

What is this study about?

Climate change means we're seeing more and more extremely hot weather events, which can be very dangerous for people's health. We know that older women, particularly those over 65, might be more vulnerable to the effects of heat than other groups. This study aims to understand why this is and, more specifically, to find out exactly what levels of heat and humidity become too much for an older woman's body to handle safely.

Your body usually has ways to cool itself down, like sweating and increasing blood flow to the skin. But there comes a point where it can't keep up, and your core body temperature starts to rise continuously. When this happens, it becomes genuinely dangerous. This study uses carefully controlled tests to identify this 'tipping point' for older women. We'll be looking at how your body temperature, heart, and even your thoughts and feelings are affected when exposed to different heat levels.

By understanding these limits, we can better protect people during heatwaves. The information we gather will help health experts create better advice and warnings, making sure everyone stays safer when temperatures soar. We're testing a new way of finding these limits to make sure it's accurate and gives us the best possible information.

Key takeaways

Understanding how older women's bodies cope with extreme heat is crucial for public safety.
The study aims to find the specific heat and humidity limits where the body can no longer cool itself.
Participants will undergo five controlled tests in a special temperature-controlled room.
Your safety is paramount, with constant monitoring and the ability to stop at any time.
Findings will help create better health advice and warnings for heatwaves.
Taking part involves physical monitoring, including internal body temperature.

Who may be eligible?

To join this study, we're looking for women who are between 65 and 85 years old. You should be a non-smoker and able to speak English or French well enough to understand information and give your consent.

It's okay if you have high blood pressure (hypertension) or Type 2 diabetes, as long as it's been at least five years since you were diagnosed. However, there are some health conditions that would mean you can't take part. These include serious recent issues with low blood sugar if you have diabetes, uncontrolled very high blood pressure, or other serious health problems that limit your physical activity or could make participating unsafe. We'll also ask about any medications you're taking.

Before you start, our medical team will do checks to make sure it's safe for you to participate. This includes checking your heart health. They'll review all your health information to ensure your safety throughout the study.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

Are you a woman between 65 and 85 years old?
Do you speak English or French?
Are you a non-smoker?
Do you have severe uncontrolled high blood pressure or other serious active health conditions?
Have you had serious low blood sugar events within the last year if you have diabetes?
Are you able to provide consent for yourself?

Answer every question to see your result.

What does participation involve?

If you join the study, you'll take part in a total of five separate study days. Each day will involve spending time in a special room where the temperature and humidity can be carefully controlled. You'll rest in a seated position while we monitor your body's responses.

On the first day, called the 'ramping trial', you'll start in a warm, humid environment (around 42°C and 28% humidity) for about an hour. Then, the humidity will slowly increase every 10 minutes until it reaches 70%. During this time, we'll be continuously measuring your internal body temperature (using a small, safe rectal thermometer) to find the point where your body starts to struggle with the heat.

On the four other study days, which will be arranged in a random order, you'll be exposed to different, but fixed, heat and humidity levels for a longer period. Some of these conditions will be slightly below your personal 'tipping point' found on the first day, one will be slightly above it, and one will be a comfortable, normal room temperature. We will compare how your body reacts in the different fixed conditions to what we saw on the first day. Throughout all trials, we'll monitor your core body temperature, heart rate, and ask you about how you're feeling and your mental sharpness. The total time for each trial day and any follow-up will be explained in detail.

Potential risks and benefits

Participating in this study might offer a small personal benefit by helping you understand your own body's response to heat. More broadly, the information we gain will significantly help improve public health advice and safety guidelines for older women during heatwaves, potentially saving lives. As with any study, there are potential risks, primarily related to heat exposure, such as feeling unwell, dizzy, or overheated. Our team will be closely monitoring you and will stop the trial immediately if you show any signs of discomfort or risk. You are always free to withdraw from the study at any time, for any reason, without it affecting your medical care outside of the study.

Locations (2)

University of Ottawa
Verified postcode
Ottawa, Canada· Not yet recruiting
University of Ottawa
Verified postcode
Ottawa, Canada· Recruiting

Common questions

Why are you only studying older women?

Research suggests older women might be more affected by extreme heat, so this study focuses specifically on understanding their body's responses to help improve safety for this group.

What does 'uncompensable heat' mean?

It means the heat is so intense that your body can no longer cool itself down effectively, causing your core body temperature to rise continuously, which can be dangerous.

Will I get too hot or be in danger?

Your safety is our top priority. We will monitor you very closely, and if you become uncomfortable or show any signs of being at risk, the trial will be stopped immediately. The heat levels are carefully controlled.

Do I need to be completely healthy to join?

Not necessarily. It's okay if you have conditions like controlled high blood pressure or Type 2 diabetes. However, we have specific health requirements to ensure your safety, which we will discuss with you.

What kind of monitoring will be done?

We'll typically measure your internal body temperature (usually with a small rectal thermometer), heart rate, and sometimes your skin temperature. We'll also ask you questions about how you're feeling and your concentration.

How to find out more

Glen P Kenny, PhD

gkenny@uottawa.ca 613-562-5800 Official trial record

Always speak to your GP or specialist before deciding to take part in a study.