Heat and Epigenetic Aging: Impacts on Older Adults

Heat May Speed Up Epigenetic Aging in Older Adults

A recent study has indicated that exposure to extreme heat may have significant implications for epigenetic aging in older adults. The findings reveal an intriguing correlation between outdoor heat and accelerated biological aging, as quantified by various epigenetic clocks. This article delves into the mechanisms through which heat affects DNA methylation, the study's methodology, and the implications for public health.

Heat Alters DNA

While warm summer days can be delightful, extreme heat poses substantial health risks, particularly for the aging population. Studies have established a link between extreme temperatures and increased rates of cardiovascular diseases as well as premature mortality [2] [3]. The process of DNA methylation serves as a biological mechanism through which organisms react to environmental stressors such as heat. Changes in DNA methylation can alter gene expression, leading to potential long-term effects on lifespan.

Although ample evidence exists regarding the impact of heat on DNA methylation in various organisms, such as worms [4] and mice [5], studies focusing on humans remain limited. Consequently, this research utilized epigenetic clocks to determine whether increases in outdoor heat correlate with accelerated aging in a sample of over 3,500 adults aged 56 and older in the United States.

Hot and Humid

The researchers computed a daily heat index following a formula provided by the National Weather Service (NWS) for each day from 2010 to 2016. This heat index combines maximum ambient temperatures and minimum humidity to assess how the temperature feels to the human body, thus affecting heat exposure levels.

According to senior author Jennifer Ailshire, a professor at the USC Leonard Davis School, "It’s really about the combination of heat and humidity, particularly for older adults, because older adults don’t sweat the same way..." This factor reduces the cooling effect that sweat evaporation provides. The NWS heat index categorizes heat exposure as follows:

The study utilized various time windows in their analysis. By examining immediate heat waves, mid-length exposures, and prolonged heat conditions, researchers assessed the cumulative health impacts and potential dose-response relationships related to heat exposure.

Hotter Days, Quicker Aging

Results indicated that elevated ambient temperatures correlate with accelerated epigenetic aging. Eunyoung Choi, a co-author and postdoctoral scholar at USC, remarked that older adults living in areas experiencing >=90°F days during half the year suffered up to 14 months of additional biological aging compared to those in regions with fewer heat days.

This finding persisted even after controlling for variables such as socioeconomic status, et cetera, highlighting that geographic exposure to heat translates into biological aging.

The Longer, The Worse

Different epigenetic clocks exhibited varying levels of sensitivity to heat exposure:

• PCPhenoAge: Consistently indicated an association between heat days and accelerated aging across all time lengths.
• PCGrimAge: Showed significant results only for longer exposure periods, demonstrating sensitivity dependent on time scale.
• DunedinPACE: Similar to PCGrimAge, the effects were notable only during extended time frames.

These variations emphasize the need for further research on how specific methylation sites contribute to biological aging when exposed to environmental heat stress. Previous studies have echoed that long-term exposure has more pronounced effects than short-term exposure [6] [7].

Everyone is Affected

The analysis also highlighted that findings were consistent among various sociodemographic subgroups, indicating no particular group was disproportionately affected by heat exposure. However, the authors acknowledged that a specialized epigenetic clock could enhance subgroup assessments.

It's pertinent to note that this analysis is based on outdoor environmental conditions. The researchers were unable to track individuals' time spent outdoors or utilize air-conditioning, leading to a potential gap in the applicability of these findings in individual risk assessments.

Risk Mitigation

The findings underscore the necessity of incorporating heat exposure into discussions surrounding health risks associated with morbidity and mortality. Addressing excessive heat exposure should be integral to shaping public health strategies and interventions.

As Ailshire posits, "If everywhere is getting warmer and the population is aging... we need to get really a lot smarter about these mitigation strategies."

Literature Cited

[1] Choi, E. Y., & Ailshire, J. A. (2025). Ambient outdoor heat and accelerated epigenetic aging among older adults in the US. Science Advances, 11(9), eadr0616.

[2] Cleland, S. E., et al. (2023). Urban heat island impacts on heat-related cardiovascular morbidity: A time series analysis of older adults in US metropolitan areas. Environment International, 178, 108005.

[3] Khatana, S. A. M., et al. (2022). Association of Extreme Heat With All-Cause Mortality in the Contiguous US, 2008-2017. JAMA Network Open, 5(5), e2212957.

[4] Wan, Q. L., et al. (2021). N6-methyldeoxyadenine and histone methylation mediate transgenerational survival advantages induced by hormetic heat stress. Science Advances, 7(1), eabc3026.

[5] Murray, K. O., et al. (2021). Exertional heat stroke leads to concurrent long-term epigenetic memory, immunosuppression, and altered heat shock response in female mice. The Journal of Physiology, 599(1), 119–141.

[6] Ni, W., et al. (2023). Associations between medium- and long-term exposure to air temperature and epigenetic age acceleration. Environment International, 178, 108109.

[7] Chiu, K. C., et al. (2024). Exposure to ambient temperature and heat index in relation to DNA methylation age: A population-based study in Taiwan. Environment International, 186, 108581.