Breaking: Scientists Discover Link Between Extreme Heat Exposure and Accelerated Biological Aging

Global warming is not just an environmental threat, but may also be silently accelerating biological aging. While extreme heat has long been associated with increased morbidity and mortality cliamte change may also be exacerbating the biological aging process. Recent evidence on the detrimental effects of extreme heat on physiological function has suggested it may also alter molecular level changes that cause a steeper decline of the aging process. A groundbreaking study by the researchers at the University of Southern California (USC) has provided convincing evidence linking chronic exposure of heat to epigenetic age acceleration, which gains new insights into how climate change may both accelerate human aging processes via environmental change.

The Science of Aging: Chronological vs. Biological Age

Aging is traditionally measured by the chronological age however this method fails to take into account differences in physiological change. Instead scientists use epigenetic clocks which analyze DNA methylation patterns (DNAm) chemical modifications that regulate gene expression to predict biological age that is a more accurate indicator of the age related decline in physiology.

The biological aging process was measured in this study using three different epigenetic clocks which measured different facets of this aging process:

• PCPhenoAge Acceleration: Predicts the onset of disease and the likelihood of mortality.

• PCGrimAge Acceleration: Estimates human lifespan along with those diseases that generally affect the aged.

• DunedinPACE (Pace of Aging): Measures the rate at which physiological degradation occurs.

By analyzing blood samples from 3, 686 elderly U.S. adults over the age of 56, alteration in the surname τiming of extreme heat exposure was found and these associations were analysed to see if this was supporting the current hypothesis that environmental stressors may be changing the epigenome in the human genome, influencing for a long period of time upon health.

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Study Design: How Heat Exposure Alters Epigenetic Aging

Every participant data on daily air temperatures for their residences from the previous six years prior to blood sample collection was analyzed to determine exposed heat levels. The heat index which combines temperature and humidity and reflects perceived heat stress was classified into standard risk levels:

• Caution (27–32°C or 80–89.6°F)

• Extreme Caution (32.2–40.6°C or 90–105°F)

• Danger (40.6–51.7°C or 105–125°F)

• Extreme Danger (>51.7°C or 125°F)

The researchers used multilevel regression models in their analysis of the relationship between exposure to heat and epigenetic age acceleration.

The results of this analysis were quite impressive as stated; it was observed that the epigenetic age was found to increase with longer periods of exposure to heat.

For every 200 days of staying above 32. 2°C (90°F) for a period of up to 6 years biological age was accelerated by up to 3. 5 months.

PCPhenoAge accelerated beyond the baseline after 2.48 years of "Extreme Caution" heat exposure.

The Period increase for PCGrimAge was 1.09 years over the same period.

Totally Tracking cumulative physiological wear by DunedinPACE showed a rapid but relatively significant increase in the order of 0. 05 years per six year period.

These findings indicate that both short term exposure as well as chronic heat stress produces epigenetic aging with the longer exposure having a greater effect.

The Epigenetic Mechanisms Behind Heat-Induced Aging

DNA methylation (DNAm) which is a key epigenetic modification is known to be responsive to environmental influences, as it alters gene expression in response to external stressors like heat exposure.

Experimental data suggest that long-term exposure to high temperatures leads to formation of maladaptive epigenetic memory which causes the cellular physiology of the organism to progress to an accelerated senescence phase whilst reducing its overall resistance; it is to be noted that such a course of events can lead to the long term altering of the function of the cell, ensuring that susceptible tissues lack resilience against environmental stressors.

Animal studies have demonstrated that prolonged heat stress can result in disrupted methylation patterns in genes which are associated with:

• Cellular repair mechanisms

• Inflammatory pathways

• Oxidative stress response

• Metabolic regulation

Due to the impairment of these crucial functions extreme heat may aggravate aging related decline which in turn may exacerbate conditions like cardiovascular disease, neurodegenerative diseases and metabolic dysregulation.

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Comparing Global Findings: The Taiwan and Germany Studies

The USC study follows on exactly from earlier work that was done previously in both Germany and Taiwan:

This earlier work once again identified correlations between heat exposure and epigenetic aging.

Ni et al. (Germany, 2021): The investigators have found that an 8-week exposure to temperatures at the 97th percentiles (18.7°C) accelerated biological age by up to 11. 71 years across different clocks of aging. A 1°C increase in annual temperature led to an increase of epigenetic aging scale coupling by 0. 24 to 2.24 years. Chiu et al. (Taiwan, 2022):

Reported that a 1 °C rise in the average 60–90 day air temperature accelerated biological aging in cancer free adults up to 44.3 days. Although in contrast to earlier studies which had considered regional populations with included criteria, the USC research were able to examine nationally representative U. S. samples which reinforced the generalizability of its findings.

Health Consequences of Heat-Induced Epigenetic Aging

While acute heat exposure is known to cause heat exhaustion, heat stroke and cardiovascular stress, longer term, sub-clinical effects of heat stress on biological aging have not been extensively looked at.

The findings propose that exposure to heat accelerates age related physiological decline thus increasing the risk of:

• Cardiovascular diseases: Dysregulation of vascular function by heat stress elevates hypertension and stroke risk.

• Cognitive decline: Epigenetic dysregulation may inhibit neuroplasticity which is associated with an risk of accelerating Alzheimer's disease progression.

• Metabolic disorders: Exhaustion of insulin sensing capacity and metabolism of lipids, when induced by heat, could lead to exacerbation of diabetes and obesity.

Limitations and Future Research Directions

In spite of the fact that the study controlled for variables like age, sex, race, wealth, smoking, alcohol use, obesity and physical activity, there are some confounding factors which remain unquantified, namely:

• Access to air conditioning and cooling resources.

• Individual heat-adaptive behaviors (e.g., hydration, time spent outdoors).

• Dietary and lifestyle factors influencing epigenetic plasticity.

Future investigations should therefore be expanded onto younger populations to achieve the goal of analysing diverse climatic regions and incorporation of genomic and transcriptomic analyses to maximise knowledge of the molecular pathways involved in coupling of heat stress to biological aging.

Public Health and Policy Implications

With projected frequency and intensity of heat waves increasing, these results strongly emphasize the need for urgent climate adaptive policies which seek to mitigate heat induced biological aging. Possible interventions include:

• Urban heat mitigation strategies: Expansion of green spaces, reflective surfaces and cooling infrastructure in high risk areas.

• Personalized heat-health monitoring: Availing wearable sensors to monitor responses to biological heat stress.

• Targeted interventions for vulnerable populations: Prioritisation of elderly population for heat prevention programs and better access to healthcare facilities.

Understanding how temperature redistributes and reshapes the human epigenome is essential to develop longer term strategies for dealing with the consequences of climate change on estrabion. As the extremes of the weather will now become the global norm, preventative measures will be essential in the steps towards controlling global health.

Call for Climate-Resilient Aging Strategies

This study displays robust evidence of chronic heat exposure to be an important cause of premature biological ageing through epigenetic modifications and highlights the unheralded health consequence of climate change, the findings go on to call for interdisciplinary research across the areas of climate science, molecular biology and public health that brings together gaps in funding to develop interventions which are designed to protect aging populations from heat induced physiological aging.

With the trajectory that global warming will have with aging and the changes in climate, this has become increasingly more apparent understanding this relationship will be vital in the future of public health and environment policy.

Reference Journal

Science Advances DOI: 10.1126/sciadv.adr0616

Journal Link Address

https://www.science.org/doi/10.1126/sciadv.adr0616

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