The Effects of Daytime, Nighttime, and Combined Heat Exposure on Human Health

Randomized Controlled Crossover Trial on the Effects of Daytime, Nighttime, and Combined Heat Exposure on Human Health

Assess the acute effects of high-temperature exposure (including both daytime and nighttime conditions) on multiple physiological and psychological indicators, including cardiovascular, respiratory, neuropsychiatric, and metabolic functions, along with their potential mechanisms.

Study Overview

• Status: Recruiting
• Conditions: Cardiovascular System; Respiratory System; Metabolism Changes; Psychology Functional Behavior
• Intervention / Treatment: Other: Daytime or Nighttime High-Temperature Exposure; Other: Daytime and nighttime neutral temperature exposure

Detailed Description

This study will be conducted in Hefei, China, as a randomized controlled crossover human exposure trial involving approximately 50 healthy young adults. The primary objective is to systematically evaluate the acute effects of heat exposure-during both daytime and nighttime-on multiple physiological and psychological domains, including cardiovascular, respiratory, neurocognitive, and metabolic functions, and to explore the underlying biological mechanisms.

A randomized crossover design will be employed, comprising three exposure phases: nighttime heat exposure, daytime heat exposure, and combined day-night heat exposure. Each participant will undergo repeated exposures under different temperature conditions, with a washout period of at least three days between sessions to minimize carryover effects.

During the nighttime exposure phase, participants will be randomly assigned to one of two sequences. Group A will first be exposed to a nighttime heat condition at 30°C from 23:00 to 07:00 (8 hours, covering habitual sleep time), followed by exposure to a thermoneutral condition at 26°C after the washout period. Group B will follow the reverse sequence.

In the daytime exposure phase, participants will again be randomized in a crossover manner. Group A will first undergo exposure to a daytime heat condition at 32°C from 09:00 to 17:00 (8 hours, approximating a typical working day), followed by exposure to a 26°C thermoneutral condition after washout. Group B will receive the reverse sequence.

In the combined day-night exposure phase, a continuous heat exposure scenario will be simulated. Group A will first be exposed to both daytime heat (32°C, 09:00-17:00) and nighttime heat (30°C, 23:00-07:00), followed by a thermoneutral condition (26°C throughout the day and night) after washout. Group B will undergo the reverse order.

Throughout each exposure session, participants will remain in a resting state to minimize the confounding effects of physical activity. Health assessments will be conducted before exposure (within 1 hour prior), during exposure, and after exposure (within 2 hours post-exposure). These assessments will include, but are not limited to, ambulatory electrocardiogram (Holter) monitoring, blood pressure measurements, spirometry, cognitive function tests, psychological questionnaires, and collection of biological samples such as blood and urine. This comprehensive evaluation will enable characterization of the acute physiological responses to heat exposure and provide insights into potential mechanistic pathways.

• Study Type: Interventional
• Enrollment (Estimated): 35
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Jian Jian Cheng; Phone Number: +86 183 5603 7837; Email: jiancheng@ahmu.edu.cn

Study Locations

• China
  • Anhui
    • Hefei, Anhui, China, 230032
      • Recruiting
      • Anhui Medical University
      • Contact: Jian Jian Cheng; Phone Number: +86 183 5603 7837; Email: jiancheng@ahmu.edu.cn

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Age 18-30;
• In good health, with no history of cardiovascular disease, respiratory disease, diabetes, endocrine disorders, neurological or psychiatric conditions;
• No smoking or alcohol addiction, no history of substance abuse;
• No prior history of particular sensitivity to high-temperature environments.

Exclusion Criteria:

• Individuals who have experienced fever, colds, infectious diseases, or significant physical trauma within two weeks prior to the high-temperature test;
• Individuals currently using medications that may affect psychological, cognitive, cardiovascular, or respiratory functions;
• Pregnant women and lactating females;
• Participants shall not be scheduled to participate during menstruation;
• Individuals with a history of fainting or severe discomfort caused by high temperatures.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Intervention / Treatment; Daytime or Nighttime High-Temperature Group	Other: Daytime or Nighttime High-Temperature Exposure; Daytime Exposure Phase: The exposure group will be exposed to high temperature (32#) in a chamber for about 8 hours, resting during the whole periods Nighttime Exposure Phase: The exposure group will be exposed to high temperature (30#) in a chamber for about 8 hours, resting during the whole periods Day-Night Combined Exposure Phase: The exposure group will be exposed continuously to high temperatures during the day and night
Other: Control; Daytime or Nighttime Neutral -Temperature Group	Other: Daytime and nighttime neutral temperature exposure; Daytime Exposure Phase: The control group will be exposed to neutraltemperature (26#) in a chamber for about 8 hours, resting during the whole periods Nighttime Exposure Phase: The control group will be exposed to neutral temperature (26#) in a chamber for about 8 hours, resting during the whole periods Day-Night Combined Exposure Phase: The control group will be exposed continuously to neutraltemperatures during the day and night

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Heart Rate Variability	Smart Band will be conducted during each exposure session. Time-domain and frequency-domain HRV indices (e.g., SDNN, RMSSD, LF, HF) will be derived to assess autonomic nervous system regulation.	Volunteers will be asked to wear smart band for 24 hours from 6:00 A.M. at the day of intervention to 6:00 A.M. at the next day.
Systolic and Diastolic Blood Pressure	Blood pressure will be measured using an automated sphygmomanometer under standardized resting conditions. Both systolic and diastolic values will be recorded.	Blood pressure will be examined before exposure and immediately (within 10 mins) after the exposure session
Forced Expiratory Volume in 1 Second	Pulmonary function will be assessed using spirometry according to standardized protocols. FEV1 will be recorded as a measure of airway function.	Lung function will be examined before exposure and half an hour after the exposure session
Forced Vital Capacity	Forced vital capacity will be measured via spirometry to evaluate lung volume and ventilatory function.	Lung function will be examined before exposure and half an hour after the exposure session
Interleukin-6	Venous blood samples will be collected and serum IL-6 concentrations will be quantified using enzyme-linked immunosorbent assay (ELISA) to assess systemic inflammatory response.	Blood will be collected 1 hour before and after the exposure session
C-reactive Protein	Serum CRP levels will be measured using high-sensitivity assays as a marker of systemic inflammation.	Blood will be collected 1 hour before and after the exposure session
F2-Isoprostanes	Plasma or urinary F2-isoprostanes will be quantified using validated assays as a stable biomarker of lipid peroxidation and oxidative stress.	Blood will be collected 1 hour before and after the exposure session
Superoxide Dismutase	Serum SOD activity will be measured to evaluate antioxidant defense capacity.	Blood will be collected 1 hour before and after the exposure session
Serum Creatinine	Serum creatinine will be measured using standard biochemical methods to assess renal function.	Blood will be collected 1 hour before and after the exposure session
Urinary Neutrophil Gelatinase-Associated Lipocalin	Urinary NGAL levels will be quantified using ELISA as an early biomarker of acute kidney injury.	Urine will be collected 1 hour before and after the exposure session
Profile of Mood States	Psychological status will be assessed using the validated POMS questionnaire to evaluate mood disturbances.	Scale assessments will be conducted within one hour before and after exposure.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Heart Rate	Heart rate will be continuously recorded during exposure using wearable devices.	Volunteers will be asked to wear smart band for 24 hours from 6:00 A.M. at the day of intervention to 6:00 A.M. at the next day.
Peak Expiratory Flow	PEF will be measured using a portable peak flow meter to assess expiratory function.	Lung function will be examined before exposure and half an hour after the exposure session
Tumor Necrosis Factor-alpha	Serum TNF-α levels will be measured using ELISA.	Blood will be collected 1 hour before and after the exposure session
Monocyte Chemoattractant Protein-1	Serum MCP-1 concentrations will be quantified to assess inflammatory activation.	Blood will be collected 1 hour before and after the exposure session
Glutathione	Reduced glutathione levels will be measured to assess antioxidant capacity.	Blood will be collected 1 hour before and after the exposure session
Blood Urea Nitrogen	Blood Urea Nitrogen will be measured using standard biochemical assays.	Blood will be collected 1 hour before and after the exposure session
Perceived Stress Scale	Perceived stress will be assessed using the validated Perceived Stress Scale questionnaire.	Scale assessments will be conducted within one hour before and after exposure.

Collaborators and Investigators

• Sponsor: Jian Cheng

Study record dates

Study Major Dates

• Study Start (Actual): June 1, 2025
• Primary Completion (Estimated): September 30, 2026
• Study Completion (Estimated): December 31, 2026

Study Registration Dates

• First Submitted: March 18, 2026
• First Submitted That Met QC Criteria: March 24, 2026
• First Posted (Actual): March 30, 2026

Study Record Updates

• Last Update Posted (Actual): March 30, 2026
• Last Update Submitted That Met QC Criteria: March 24, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Other Study ID Numbers: 81250681

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No