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Exposure to indoor air pollution during childhood tends to be linked to poorer cognitive health in older adulthood. This suggests that access to clean energy early in life might help protect the brain as it ages. These findings come from a recent study published in Social Science & Medicine, which provides evidence that growing up in homes using solid fuels for cooking can set off a chain of disadvantages that affect memory and thinking skills decades later.
Xu Zong conducted the new study to explore a gap in our understanding of how early environmental exposures shape aging. While many scientists have established that breathing polluted air during adulthood increases the risk of cognitive decline, the long-term impact of breathing indoor air pollution during childhood remained mostly unexplored. Around the world, billions of people still rely on solid fuels like coal and wood for daily cooking and heating. This practice fills homes with toxic pollutants.
“I am interested in understanding how early-life living conditions, specifically indoor air pollution, may have long-term consequences for cognitive health. Air pollution has been highlighted by The Lancet as one of the modifiable risk factors for dementia. While much research has focused on adult exposures or urban outdoor pollution, there was a gap in linking childhood indoor environments to cognitive outcomes later in life,” said Zong, a researcher at the Max Planck – University of Helsinki Center for Social Inequalities in Population Health.
Zong wanted to see if breathing these pollutants during the first seventeen years of life creates a lasting ripple effect. From a life course perspective, childhood experiences shape a person’s entire biological and social trajectory. Early exposure to pollution might hinder brain development directly or cause other health issues that eventually weaken the brain’s resilience. By viewing cognitive aging as a lifelong process, Zong aimed to trace how early disadvantages might accumulate and eventually influence mental sharpness in middle and old age.
To investigate this, Zong analyzed data from a large, nationally representative survey called the China Health and Retirement Longitudinal Study. The final sample included 7,161 adults living in China who were 45 years of age or older. Participants answered questions about their life histories, including the primary type of cooking fuel their families used from the time they were born until they turned seventeen. Zong categorized these individuals into two groups based on whether they relied on solid fuels or had access to clean energy like electricity or natural gas.
To measure cognitive performance, the participants completed several standardized mental tasks. The tasks assessed episodic memory, which involves the ability to recall recent events or information, through memory recall tests. They also measured mental intactness, which involves basic thinking skills, by asking participants to do simple math, redraw a picture, and correctly state the current date. Together, these tasks measure fluid cognition, a type of mental processing that is highly sensitive to aging.
Zong applied an advanced statistical technique called a causal forest approach to analyze the data. This is a machine learning method that helps scientists estimate the effects of a specific variable while accounting for complex relationships among many different factors. The analysis controlled for several background details that might influence the results, such as the participants’ age, gender, marital status, and the education levels of their parents.
The results showed that individuals exposed to indoor air pollution throughout their childhood tended to have significantly poorer cognitive performance in later life. This negative association was evident in both their episodic memory and their mental intactness. Out of the 7,161 participants, 96 percent had grown up in homes using solid fuels. These individuals consistently scored lower on the cognitive tests than the 4 percent who grew up using clean energy.
The research also provides evidence explaining how this early exposure translates into cognitive deficits decades later. Zong tested three potential pathways connecting early life to late life: biological, psychological, and socioeconomic. The data suggests that biological factors act as connecting bridges between early pollution exposure and later cognitive decline. For instance, childhood pollution exposure was linked to a higher body mass index and more physical limitations in daily activities during adulthood.
Body mass index is a measure of body fat based on height and weight, and higher levels are linked to various health issues. Limitations in daily activities refer to difficulties with basic self-care tasks like dressing or bathing. Both of these biological factors represent a decline in physical health that can accelerate cognitive aging. On the other hand, inflammation levels, measured by a blood marker called C-reactive protein, did not seem to bridge the gap between early pollution exposure and later-life cognitive decline.
Socioeconomic factors also played a major mediating role in the study. Individuals exposed to indoor air pollution as children often completed less education and earned lower incomes as adults. These social and economic disadvantages are known to limit intellectual stimulation and access to healthcare, which tends to speed up cognitive aging. Meanwhile, psychological factors, such as experiencing symptoms of depression, did not show a significant linking effect in this specific analysis.
“We were somewhat surprised by the persistence of the association even after accounting for socioeconomic factors and other childhood conditions,” Zong told PsyPost. “Biological mediators such as BMI and limitations in daily living activities significantly mediated this association.”
“Our analysis also revealed indirect effects through adult education and income, highlighting the role of socioeconomic pathways. Children exposed to indoor air pollution may follow a disadvantaged life trajectory, limiting educational attainment and economic mobility, which in turn is associated with faster cognitive aging and higher risk of cognitive decline.”
Zong also looked at how different groups of people responded to the long-term effects of childhood pollution. The results showed that men, people who had a history of smoking, and people who regularly consumed alcohol were particularly vulnerable. These groups experienced a more pronounced drop in cognitive performance if they had been exposed to indoor air pollution early in life. Zong suggests this might be due to a combination of lifestyle choices and early environmental insults, which together create a heavier burden on the body over time.
“Our findings suggest that early-life indoor air quality matters for cognitive development and lifelong cognitive health,” Zong explained. “Improving access to clean energy (such as electricity and natural gas) in homes could help prevent cognitive decline from the very beginning.”
“While the effects are modest at the individual level, they are meaningful at the population level and highlight the importance of environmental interventions in childhood. Considering that nearly 30% of the global population, roughly 2.4 billion people, still cook without clean fuels, this issue is relevant not only in low- and middle-income countries but also in some populations in high-income countries, where the use of solid fuels has increased due to higher energy prices following the Ukraine war.”
It is important to recognize that this study is observational, meaning it shows associations but cannot prove strict cause and effect. One limitation is that participants had to recall the type of fuel their families used decades ago, which leaves room for memory errors. This is especially true when studying older adults who might already be experiencing some memory loss.
Additionally, because the vast majority of the older adults in this sample used solid fuels, the group of unexposed individuals was relatively small. Although this small group represents millions of people in the general population, the imbalance makes statistical comparisons more challenging. Because the study focused on older adults in China, the results might not perfectly apply to younger generations or people living in other countries.
Zong plans to use data tracked over longer periods of time to better understand the exact causal relationships. Future research will also test whether these findings hold true in different global populations. By studying how early environments shape lifelong health, scientists hope to find new ways to protect aging brains from the very beginning.
The study, “The long arm of childhood: The association between early-life indoor air pollution exposure and cognitive performance in later life,” was authored by Xu Zong.
