🧬 biology

Lifetime perceived thermal stress impacts brain and behavior in healthy young adults.

This study of 5,851 healthy young adults reveals that a lifetime of perceived thermal stress has persistent, cumulative effects on brain structure, psychological well-being, and lifestyle behaviors, suggesting that subjective thermal discomfort is a critical factor in evaluating thermal-related neurological alterations.

Original authors: Chunshui Yu, Yuan Ji, Caihong Wang, Xiaojun Xu, Zhihan Yan, Meiyun Wang, Long Jiang Zhang, Zuojun Geng, Yongqiang Yu, Weihua Liao, Hui Zhang, Bo Gao, Tong Han, Zhenwei Yao, Quan Zhang, Meng Liang, Wen

Published 2026-08-04

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Chunshui Yu, Yuan Ji, Caihong Wang, Xiaojun Xu, Zhihan Yan, Meiyun Wang, Long Jiang Zhang, Zuojun Geng, Yongqiang Yu, Weihua Liao, Hui Zhang, Bo Gao, Tong Han, Zhenwei Yao, Quan Zhang, Meng Liang, Wen Qin, Feng Liu, Qiang Xu, Jiayuan Xu, Nana Liu, Jie Tang, Sijia Wang, Xue Hui, Haiyan Li, Shuqi Yang, Zhaoxiang Ye, Peng Zhang, Wei Li, Wei Wei, Dapeng Shi, Su Lui, Feng Chen, Jing Zhang, Wen Shen, Yanwei Miao, Dawei Wang, Jia-Hong Gao, Yunjun Yang, Junfang Xian, Wenzhen Zhu, Kai Xu, Bing Zhang, Xiaochu Zhang, Shijun Qiu, Guangbin Cui, Xi-Nian Zuo, the CHIMGEN Consortium the CHIMGEN Consortium

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ⚕️ This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer

Imagine your brain as a high-tech city, constantly under construction. Just like a city needs to manage traffic, power, and waste, your brain manages signals, connections, and structures. Now, imagine the weather outside this city. For a long time, scientists thought that just knowing the air temperature was enough to understand how the weather affects the city's construction. But there's a catch: the air temperature doesn't tell the whole story. It doesn't account for how the wind chills your skin, how the sun beats down on your roof, or how humidity makes the air feel heavy. To get the real picture, scientists use a special "feels-like" score called the Universal Thermal Climate Index (UTCI). This score combines all those factors to tell us exactly how much stress the weather puts on a human body.

Why does this matter? We are living in a world where extreme heat is becoming more common. We know that heat can make people sick or even cause accidents, but we didn't know if living in a hot, stressful climate for your whole life could actually change the physical shape of your brain or how you act. This is the big question: Does the "feels-like" heat you've experienced since you were born leave a permanent mark on your brain's architecture and your personality, even if you are perfectly healthy?

The Great Heat Detective Story

A massive team of researchers, part of a group called the CHIMGEN Consortium, decided to play detective. They didn't just look at one person or one city; they gathered data from 5,851 healthy young adults (aged 18 to 30) from all over China. These weren't patients with brain diseases; they were a super-healthy group, which made the study even more interesting. If heat stress could change their brains, it would be a very strong signal that it affects everyone.

The team built a unique "heat resume" for each person. Instead of just checking the weather on the day they got an MRI scan, they tracked the weather at every place these young people had lived from the moment they were born until the day of the scan. They calculated two main scores:

TSD-26: The percentage of hours in their lives where the "feels-like" temperature was above 26°C (a bit uncomfortable).
TSD-32: The percentage of hours where it was above 32°C (strong heat stress).

Then, they compared these heat scores to three big things: how the participants lived (lifestyle), what their brains looked like (MRI scans), and how they thought and felt (behavior).

The Brain's Blueprint: Shrinking and Swelling

When the scientists looked at the brain scans, they found some surprising changes in the city's architecture. People who had spent more hours in uncomfortable or strong heat stress showed:

Smaller cerebral volumes: The main part of the brain (the cerebrum) was slightly smaller in several regions. It's as if the heat stress caused the city's main districts to shrink a little bit.
Larger cerebellar volumes: Interestingly, the cerebellum (a part of the brain at the back, often linked to balance and coordination) was slightly larger.
Weaker connections: The "wiring" between different parts of the brain, specifically in a bridge called the corpus callosum, showed lower integrity. Think of this as the roads between city districts becoming a bit more bumpy or less efficient.

These findings suggest that a lifetime of feeling hot might physically reshape the brain, even in young, healthy people.

The Lifestyle Shift: What We Eat and How We Sleep

The heat didn't just change the brain; it seemed to change how people lived their lives, too. The study found that people with higher lifetime heat stress:

Changed their taste buds: They tended to like sour and spicy foods less.
Changed their diet: They ate fish and poultry more often.
Struggled with sleep: They reported more "daytime dysfunction," meaning they felt groggy, tired, or less enthusiastic during the day, even if they thought they slept okay at night.

It's like the heat stress rewired their daily habits, perhaps as a way to cope with the constant warmth.

The Personality Puzzle: Fear, Curiosity, and Happiness

Perhaps the most fascinating part was how heat stress linked to personality and mood. The study suggested that people with more lifetime heat stress tended to:

Be more cautious: They scored higher on "harm avoidance," meaning they were more sensitive to potential threats.
Seek novelty: They also scored higher on "novelty seeking," showing a stronger desire for new and exciting experiences.
Care less about social rewards: They had lower "reward dependence," suggesting they might rely less on social approval or attachment.
Feel less happy: They reported lower overall psychological well-being.

The "When" Matters: Sensitive Windows

The researchers didn't just look at the total heat; they asked, "Does it matter when you felt the heat?" Using a special time-traveling math model, they found that the brain and behavior are most sensitive to heat stress at specific ages.

For example, heat stress at age 8 seemed to change taste preferences, while heat at age 17 influenced poultry intake.
For brain structure, heat at age 1 made a certain part of the brain larger, but heat at ages 12–13 made that same part smaller.
This means the brain isn't just a sponge that soaks up heat equally all the time; it has specific "construction windows" where it is more vulnerable to the weather.

The Pathway: Direct Hits and Detours

Finally, the team tried to figure out how the heat caused these changes. Did the heat go straight to the brain, or did it change your lifestyle first, which then changed your brain?

Direct Hits: The study suggests that heat stress mostly hits the brain directly. It's like a direct hit on the city's construction site, changing the structure without needing a middleman.
Detours: However, for some behaviors (like how much you worry or how happy you feel), the heat did take a detour. It changed your sleep or your diet first, and those changes then influenced your personality.

The Bottom Line

This paper suggests that the "feels-like" heat we experience over our entire lives leaves a lasting fingerprint on our brains and behaviors, even in people who are otherwise very healthy. It's not just about feeling hot for a day; it's about the cumulative weight of a lifetime of thermal stress. While the changes found were small, finding them in such a healthy group suggests that the effect might be even stronger in more vulnerable people. The study also highlights that we need to look beyond simple air temperature and consider the full "feels-like" experience to truly understand how climate change might be reshaping human biology.

Technical Summary: Lifetime Perceived Thermal Stress Impacts Brain and Behavior in Healthy Young Adults

Problem Statement
As global temperatures rise, extreme thermal exposure is increasingly linked to adverse health outcomes, including mortality, morbidity, and specific brain-related diseases (e.g., stroke, Alzheimer's, depression). However, existing research predominantly relies on outdoor air temperature as a proxy for thermal exposure. This metric fails to capture the physiological reality of human-perceived thermal stress, which is modulated by wind speed, solar radiation, humidity, clothing, and metabolic activity. Consequently, the specific effects of perceived thermal stress on brain structure, function, lifestyle, and behavior in healthy populations remain unclear. Furthermore, previous studies often lack the granularity to distinguish between cumulative lifetime effects and critical sensitive periods during development, or to disentangle direct biological impacts from indirect effects mediated by lifestyle adaptations.

Methodology
This study leveraged data from the Chinese Imaging Genetics (CHIMGEN) consortium, a large-scale prospective cohort of 7,306 healthy Han Chinese adults (aged 18–30) recruited from 31 centers across mainland China. The analysis focused on 5,851 participants who provided complete residential coordinates from birth to the time of MRI scanning.

Exposure Assessment: The study utilized the Universal Thermal Climate Index (UTCI), derived from the ERA5-HEAT reanalysis dataset (1940–present), to quantify human-perceived thermal stress. Two cumulative exposure metrics were calculated for each participant: Thermal Stress Duration (TSD)-26 (proportion of lifetime hours with UTCI > 26°C, indicating uncomfortable stress) and TSD-32 (proportion of hours with UTCI > 32°C, indicating strong heat stress).
Phenotyping:
- Lifestyle: 31 items covering dietary habits (22 items), sleep quality (7 items, PSQI), and mobile phone usage (2 items).
- Brain Imaging: 449 MRI phenotypes including grey matter volume (GMV) of 124 regions, cortical surface area (SA) and thickness (CT) of 62 regions, fractional anisotropy (FA) of 48 white matter tracts, and functional connectivity between 18 resting-state networks.
- Behavior: 28 measures encompassing 11 personality traits, 7 mental health indicators, and 10 cognitive assessments.
Statistical Analysis:
- Association Analysis: Linear regression models were fitted to assess associations between lifetime TSD and all phenotypes, adjusting for age, sex, education, family socioeconomic status (SES), and lifetime average NDVI. Missing data were handled via Multiple Imputation by Chained Equations (MICE), generating 10 datasets with results pooled via Rubin's rules. Significance was corrected for the effective number of tests (n=288), setting a threshold of $P < 1.74 \times 10^{-4}$ .
- Sensitive Periods: Distributed Lag Models (DLMs) were employed to identify specific age windows (0–18 years) where annual TSD significantly influenced adult outcomes.
- Pathway Analysis: Structural Equation Modeling (SEM) was used to characterize direct effects of thermal stress on brain/behavior and indirect effects mediated by lifestyle factors.
- Robustness: Sensitivity analyses included subsampling, alternative regression models (proportional-odds logistic), non-imputed data verification, and adjustment for air pollutants (PM2.5, NO2).

Key Results
The study identified significant associations between lifetime perceived thermal stress and multiple domains of health in this exceptionally healthy cohort:

Lifestyle Outcomes: Higher TSD-26 was associated with weaker preferences for sour and spicy tastes, higher frequency of fish and poultry intake, and greater daytime dysfunction related to sleep quality. TSD-32 was associated with weaker sour and spicy preferences. Sensitive period analysis revealed that specific ages (e.g., age 8 for taste preferences, age 5 for sleep dysfunction) were particularly influential for these lifestyle changes.
Brain Imaging Outcomes:
- Structure: Higher TSD-26 was associated with smaller GMV in 11 cerebral regions and larger GMV in two cerebellar regions. Both TSD-26 and TSD-32 were associated with reduced FA in the body of the corpus callosum. TSD-32 additionally correlated with lower FA in the left superior longitudinal fasciculus and thinner left lateral occipital cortex.
- Sensitive Periods: DLMs identified divergent effects at different ages. For instance, higher TSD-26 at age 1 was associated with larger GMV in the left inferior temporal gyrus, whereas exposure at ages 12–13 was associated with smaller GMV in the same region.
Behavioral Outcomes: Higher TSD-26 was linked to greater harm avoidance and novelty seeking, but lower reward dependence and reduced psychological well-being. TSD-32 was similarly associated with higher harm avoidance and lower well-being. Sensitive periods were identified for novelty seeking (ages 5–7 vs. 17) and reward dependence (ages 0–1 and 9–11 vs. 3–6).
Pathways: SEM analysis indicated that thermal stress affects brain phenotypes primarily through direct effects. However, behavioral outcomes were partially mediated by lifestyle alterations; for example, the association between TSD-26 and harm avoidance was mediated by sleep-related daytime dysfunction and fish intake.

Significance and Claims
The authors claim that this study provides the first comprehensive evidence that lifetime perceived thermal stress has persistent, measurable impacts on brain structure, personality, and mental well-being, even in a cohort of "extraordinarily healthy" young adults.

Physiological Relevance: By utilizing UTCI rather than air temperature, the study demonstrates that human-perceived thermal stress is a more sensitive and biologically relevant index for assessing thermal exposure impacts.
Developmental Sensitivity: The identification of sensitive periods (with some showing congruent or incongruent effect directions relative to cumulative effects) suggests that the timing of thermal exposure is critical, offering potential targets for targeted interventions.
Mechanistic Insight: The findings support a model where thermal stress impacts the brain both directly (potentially via neuroinflammation) and indirectly through lifestyle adaptations (diet and sleep), which in turn influence behavior.
Generalizability: The authors posit that because significant effects were detected in a narrow, healthy age range with minimal confounding, perceived thermal stress is a robust metric for evaluating thermal risks in more vulnerable populations, such as those with pre-existing brain diseases.

The paper concludes with modesty regarding its limitations, acknowledging the cross-sectional nature of the neuroimaging data, reliance on self-reported lifestyle measures, and the restriction to a specific demographic (young Han Chinese adults), noting that future longitudinal work in diverse populations is necessary to fully clarify long-term consequences.