Warm Water Immersion for Temperature Regulation in Aging

Overseen By Glen P Kenny, PhD

Age: 65+

Sex: Female

Trial Phase: Academic

Sponsor: University of Ottawa

Disqualifiers: Severe hypoglycemia, Uncontrolled hypertension, Cardiac abnormalities, others

No Placebo Group All trial participants will receive the active study treatment (no placebo)

Compensation: Varies

Number of Visits: 9

Duration: 7 days

12 Participants Needed

What You Need to Know Before You Apply

What is the purpose of this trial?

This trial examines how soaking in warm water can help older women better manage hot indoor temperatures. As global warming increases the frequency of heat waves, the study investigates whether a 7-day warm-water immersion (heat acclimation therapy) can reduce stress on the body and heart during heat exposure. It targets women with high blood pressure or type 2 diabetes who have not experienced severe complications from these conditions. Participants must not smoke and should speak English or French. The goal is to find a way to help women stay safe during extreme heat, particularly if they lack air conditioning. As an unphased trial, this study provides a unique opportunity to contribute to innovative research that could enhance heat resilience for many.

Will I have to stop taking my current medications?

The trial does not specify if you need to stop taking your current medications. However, if you or the investigators believe that your medication use makes participation inadvisable, it may affect your eligibility.

What prior data suggests that warm-water immersion is safe for older adults?

Research has shown that soaking in warm water can be a safe and comfortable way for older adults to acclimate to heat. One study found that middle-aged individuals generally tolerated hot water immersion well, while younger adults sometimes experienced dizziness, indicating age-related differences in reactions.

Another study examined a 7-day warm-water immersion routine and found it could help older adults lose body heat more effectively. This suggests it might aid in coping with heat, particularly for those without air conditioning.

Overall, passive heat therapy, such as soaking in warm water, appears to improve heart and blood vessel health in older adults, potentially enhancing their cardiovascular function.

This trial aims to explore the effectiveness of this method, but current research supports the safety of warm-water immersion for helping older adults acclimate to heat. ^{1 2 3 4 5}

Why are researchers excited about this trial?

Researchers are excited about the trial exploring heat acclimation through warm-water immersion for temperature regulation in aging because it offers a novel, non-pharmacological approach to managing heat stress, which is particularly relevant for seniors. Unlike typical strategies that might involve cooling devices or medications to manage body temperature, this method leverages the body's natural ability to adapt to heat through gradual exposure. By using warm-water immersion, the body may improve its ability to regulate temperature during extreme heat events, potentially reducing heat-related health risks for the elderly without relying on drugs or external cooling systems. This method could empower individuals to enhance their resilience to heat in a sustainable and accessible way.

What evidence suggests that warm-water immersion is effective for temperature regulation in aging?

Research has shown that soaking in warm water can help older adults cope better with heat. Studies found that spending time in warm water for seven days improved the body's cooling ability and reduced both body temperature and heart strain. This is important because it can lessen stress on the heart and body during hot weather. By increasing heat resistance, this method might protect older adults from overheating indoors, especially without air conditioning. While current findings are encouraging, more research is needed to confirm these benefits in everyday situations.

In this trial, participants will undergo a warm-water immersion protocol to assess its effectiveness in improving temperature regulation. Additionally, they will experience daylong exposure to indoor overheating conditions to evaluate the impact of warm-water immersion on their ability to cope with heat. ^{1 2 6 7 8}

Who Is on the Research Team?

Glen P Kenny, PhD

Principal Investigator

University of Ottawa

Are You a Good Fit for This Trial?

This trial is for older females who may be vulnerable to heat-related issues due to lack of air-conditioning or reliable electricity. It's designed to help them become more resistant to heat by using warm-water baths. Participants should not have conditions that prevent them from safely experiencing increased temperatures.

Inclusion Criteria

Non-smoking

Ability to provide informed consent

I have had high blood pressure or type 2 diabetes for over 5 years.

Exclusion Criteria

My blood pressure is not higher than 150/95 mmHg.

Cardiac abnormalities identified during screening

Use of or changes in medication judged by the patient or investigators to make participation in this study inadvisable

Timeline for a Trial Participant

Screening

Participants are screened for eligibility to participate in the trial

2-4 weeks

Baseline Assessment

Participants undergo baseline assessment of heat and cardiovascular responses during a 10-hour passive heat exposure

1 day

1 visit (in-person)

Treatment

Participants undergo a 7-day passive heating protocol with warm-water immersion

7 days

7 visits (in-person)

Post-Treatment Assessment

Participants undergo post-treatment assessment of heat and cardiovascular responses during a 10-hour passive heat exposure

1 day

1 visit (in-person)

Follow-up

Participants are monitored for safety and effectiveness after treatment

4 weeks

What Are the Treatments Tested in This Trial?

Interventions

• Heat acclimation by warm-water immersion

Trial Overview

The study tests if soaking in warm water can make older women better at handling extreme indoor heat, without exercising. For seven days, they'll immerse in warm water with their core temperature maintained around 38.5°C for the last hour, and then face an 8-hour indoor heat challenge.

How Is the Trial Designed?

Group I: Daylong exposure to indoor overheating Experimental Treatment 1 Intervention

Prior to and following the warm-water immersion protocol, participants will undergo a 10-hour passive heat exposure where they will remain in a climate-controlled chamber regulated at 36°C and 45% humidity (temperatures experienced indoors during extreme heat events in North America). During this time they will remain seated with the exception of hourly 5-minute breaks to stretch.

Who Is Running the Clinical Trial?

University of Ottawa

Lead Sponsor

Trials

231

Recruited

267,000+

Published Research Related to This Trial

Heat acclimation enhances the body's ability to regulate temperature by shifting the thresholds for heat dissipation and thermal injury, which allows for better performance in high temperatures.

Molecular mechanisms, including the expression of protective proteins like HSP70 and HSF1, play a crucial role in the acclimation process, suggesting that both physiological and cellular adaptations are important for developing heat tolerance.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat acclimation, epigenetics, and cytoprotection memory. Horowitz, M.[2022]

A 2-hour immersion in 42°C hot water significantly increased the vastus lateralis muscle temperature by about 2.8°C, which is beneficial for cellular adaptation and muscle growth.

The hot-water immersion protocol was found to be safe and well-tolerated, with no significant changes in blood pressure and only moderate increases in heart rate and thermal sensation, indicating it can be used for health-related purposes.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Muscle temperature kinetics and thermoregulatory responses to 42 °C hot-water immersion in healthy males and females. Rodrigues, P., Trajano, GS., Wharton, L., et al.[2021]

Daily hot water immersion (HWI) after exercise for 6 days led to significant heat acclimation in 17 male participants, evidenced by lower resting and exercise-induced rectal temperatures in both temperate and hot conditions.

HWI improved endurance performance by 4.9% during a 5-km time trial in hot conditions (33°C), while no performance changes were observed in the control group, highlighting HWI as an effective strategy for enhancing exercise performance in heat.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat. Zurawlew, MJ., Walsh, NP., Fortes, MB., et al.[2022]

In a study comparing nine healthy older men and eleven young men during severe lower-body heating, older men showed a significantly lower rate of temperature increase in core body temperature, indicating a delayed thermoregulatory response as they aged.

Older men experienced greater heat accumulation in their calf muscles and skin compared to younger men, suggesting that aging affects the body's ability to transfer heat effectively from lower to upper body areas during hyperthermia.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat transfer and loss by whole-body hyperthermia during severe lower-body heating are impaired in healthy older men. Brazaitis, M., Paulauskas, H., Eimantas, N., et al.[2018]

Heat acclimation enhances the body's ability to tolerate extreme temperatures by activating protective pathways that produce molecules capable of combating various stressors, a process known as heat acclimation-mediated cross-tolerance (HACT).

HACT leads to long-lasting protective effects across different organs, characterized by increased reserves of cytoprotective proteins and epigenetic changes that help the body quickly return to a protected state after stress exposure.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat Acclimation-Mediated Cross-Tolerance: Origins in within-Life Epigenetics? Horowitz, M.[2020]

Heat acclimation leads to significant physiological changes that enhance the body's ability to manage extreme heat, including a lower temperature threshold for heat dissipation and improved circulatory reserves, as observed in a rat model.

Long-term heat acclimation (LTHA) results in increased efficiency of thermal regulatory mechanisms, partly due to changes in gene expression and enhanced levels of heat shock proteins, which help protect cells from thermal injury.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

From molecular and cellular to integrative heat defense during exposure to chronic heat. Horowitz, M.[2019]

The study involved 13 participants undergoing passive heat acclimation (HA) through lower body immersion in hot water, which improved physiological symptoms like reduced heart rate and increased sweating capacity.

Despite these improvements, the heat acclimation did not alter levels of central or peripheral fatigue during exercise in hot conditions, indicating that while HA enhances physiological responses, it does not necessarily mitigate fatigue effects from hyperthermia.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Heat acclimation does not reduce the impact of hyperthermia on central fatigue. Brazaitis, M., Skurvydas, A.[2022]

Head-out immersion in hot water (42°C) increased core body temperature in both elderly (66-75 years) and young males (21-32 years), but the increase was less pronounced in the elderly, indicating age-related differences in temperature regulation.

While young participants showed a significant rise in serum interleukin-6 levels one hour after immersion, elderly participants did not experience any change, suggesting that aging may affect the body's inflammatory response to heat exposure.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Attenuation of core temperature elevation and interleukin-6 excretion during head-out hot water immersion in elderly people. Yamashiro, M., Nishimura, Y., Mikami, Y., et al.[2020]

Aging affects human temperature regulation, leading to changes in baseline body core temperature and circadian temperature rhythms, as well as reduced physiological responses to cold stress, such as less effective peripheral vasoconstriction and lower metabolic heat production.

Despite increased mortality risks from extreme temperatures in older adults, studies suggest that age alone does not significantly impair thermoregulation, as factors like fitness level and chronic diseases play a more critical role in thermal tolerance.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Invited review: aging and human temperature regulation. Kenney, WL., Munce, TA.[2022]

Reinduction of heat acclimation (ReAC) occurs significantly faster than initial acclimation, taking only 2 days compared to 30 days, suggesting the presence of 'molecular memory' that aids in this rapid process.

Gene profiling revealed that even after a month of deacclimation, key stress-related genes remained activated, indicating that the molecular changes associated with heat acclimation persist beyond the physiological adaptations, highlighting the role of chromatin remodeling in maintaining acclimatory memory.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Physiological and molecular evidence of heat acclimation memory: a lesson from thermal responses and ischemic cross-tolerance in the heart. Tetievsky, A., Cohen, O., Eli-Berchoer, L., et al.[2023]

In a study comparing six older men (average age 61) and six young men (average age 26) during heat exposure, older individuals showed a lower heart rate during heat acclimation, indicating a potential difference in cardiovascular response to heat stress.

Both age groups benefited from a 9-day heat acclimation, resulting in lower baseline body temperatures during heat exposure, but older men had a reduced ability to increase forearm blood flow and sweating rates compared to younger men, suggesting age-related differences in thermoregulatory function.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Effects of age and acclimation on responses to passive heat exposure. Armstrong, CG., Kenney, WL.[2022]

Heat acclimation (HA) improved thermoregulation, perceived exertion, and exercise performance in both young and elderly participants, indicating its efficacy across age groups.

Both exercise-based heat acclimation and post-exercise hot water immersion are effective methods for preparing elderly individuals to handle heat stress, with no significant differences in outcomes between the two approaches.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

Exercise heat acclimation and post-exercise hot water immersion improve resting and exercise responses to heat stress in the elderly. Waldock, KAM., Gibson, OR., Relf, RL., et al.[2021]

The critical thermal maximum (CTmax) in zebrafish showed moderate repeatability, with an initial increase in tolerance due to thermal acclimation, indicating that individuals can adapt to heat stress over time.

Repeated CTmax trials did not negatively impact growth or survival rates (99% survival), supporting the method's safety and relevance for assessing thermal tolerance in aquatic species.

NCBI (Pubmed)

pubmed.ncbi.nlm.nih.gov

CTmax is repeatable and doesn't reduce growth in zebrafish. Morgan, R., Finnøen, MH., Jutfelt, F.[2019]

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