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

Trial Summary

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 data supports the effectiveness of the treatment Heat acclimation by warm-water immersion for temperature regulation in aging?

Research shows that warm-water immersion can help older adults better manage heat stress by improving their body's response to heat. Studies indicate that while older adults may have a delayed heat transfer compared to younger individuals, warm-water immersion can still increase core body temperature and help with heat acclimation. ^{1 2 3 4 5}

Is warm water immersion safe for older adults?

Research shows that older adults may experience a delay in heat transfer and greater heat accumulation in their bodies during warm water immersion, but no specific safety issues were reported. It's important for older adults to be cautious and monitor their body's response during such treatments. ^{2 4 6 7 8}

How does warm-water immersion for heat acclimation differ from other treatments for temperature regulation in aging?

Warm-water immersion for heat acclimation is unique because it uses the body's natural ability to adapt to heat by enhancing protective pathways and adjusting gene expression, which helps the body better manage temperature changes. This approach is different from other treatments as it focuses on long-term adaptation and memory of heat tolerance, rather than immediate relief or external cooling methods. ^{9 10 11 12 13}

What is the purpose of this trial?

As overheating in buildings is expected to increase as global warming continues, proactive measures to increase heat resiliency in heat-vulnerable older people are needed, especially for those without access to home cooling or reliable sources of electricity. While short-term heat acclimation through exercise in the heat has been shown to increase heat dissipation and decrease both the physical and mental stress imposed on individuals exposed to heat, such protocols are not tenable for older, sedentary adults. A recent report showed that seven consecutive days of warm-water immersion improved whole-body heat loss and reduced physiological strain as assessed during an exercise-heat stress in habitually active older men This represents a critical finding as an increase heat-loss capacity would serve as an important safeguard for older adults exposed to indoor overheating due to lack of air-conditioning. While this preliminary data highlights passive hot water immersion as a promising strategy for increasing heat-resilience in vulnerable adults, work is needed to confirm its efficacy in more "real-world" environments. Thus, this study aims to assess the effectiveness of a 7-day passive heating (warm-water immersion with core temperature clamped at \~38.5°C for the final 60 minutes) protocol in mitigating increases in thermal and cardiovascular strain in older females exposed to daylong (10-hours) indoor overheating (36°C, 45% relative humidity) prior to and following the passive heating intervention. Relative to males, females have a reduced heat loss capacity (\~5%), which is driven by differences in the activation of heat loss responses (i.e., skin blood flow and sweating). Although there have been mixed findings with regards to the influence of sex as a mediating factor for heat-related mortality, some studies suggest that females are at a higher risk of heat-related mortality and morbidity compared to males, especially amongst older individuals (≥65 years). Notably, a greater proportion of older females died compared to their male counterparts during the 2021 Western Heat Dome. While the underlying causes for these differences remain unclear, greater cardiovascular strain may place females at higher mortality risk during extreme heat.

Research Team

Glen P Kenny, PhD

Principal Investigator

University of Ottawa

Eligibility Criteria

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

Ability to provide informed consent

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

Non-smoking

Exclusion Criteria

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

I've had severe low blood sugar or can't tell when my sugar is low in the last year.

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

Timeline

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

Treatment Details

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.

Participant Groups

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+

Findings from Research

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]

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]

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]

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]

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]

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 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]

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]

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]

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]

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 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]

References

1. Australia 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. [2021]

2. England pubmed.ncbi.nlm.nih.gov

Heat transfer and loss by whole-body hyperthermia during severe lower-body heating are impaired in healthy older men. [2018]

3. Japan pubmed.ncbi.nlm.nih.gov

Attenuation of core temperature elevation and interleukin-6 excretion during head-out hot water immersion in elderly people. [2020]

4. Germany pubmed.ncbi.nlm.nih.gov

Muscle temperature kinetics and thermoregulatory responses to 42 °C hot-water immersion in healthy males and females. [2021]

5. United States pubmed.ncbi.nlm.nih.gov

Invited review: aging and human temperature regulation. [2022]

6. Denmark pubmed.ncbi.nlm.nih.gov

Post-exercise hot water immersion induces heat acclimation and improves endurance exercise performance in the heat. [2022]

7. United States pubmed.ncbi.nlm.nih.gov

Effects of age and acclimation on responses to passive heat exposure. [2022]

8. Germany pubmed.ncbi.nlm.nih.gov

Heat acclimation does not reduce the impact of hyperthermia on central fatigue. [2022]

9. United States pubmed.ncbi.nlm.nih.gov

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

10. United States 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. [2023]

11. Switzerland pubmed.ncbi.nlm.nih.gov

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

12. United States pubmed.ncbi.nlm.nih.gov

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

13. England pubmed.ncbi.nlm.nih.gov

CTmax is repeatable and doesn't reduce growth in zebrafish. [2019]