Exposure to indoor air pollution during childhood tends to lead to poorer cognitive function later in life. This suggests that access to clean energy early in life may help protect the brain as we age. These discoveries are Social science and medicineThis provides evidence that growing up in a household that uses solid fuels for cooking can cause a chain of disadvantage that affects memory and thinking skills decades later.
Xu Zong conducted new research to explore gaps in our understanding of how early environmental exposures shape aging. Although many scientists have established that breathing polluted air in adulthood increases the risk of cognitive decline, the long-term effects of breathing indoor air pollution in childhood are largely unknown. Billions of people around the world still rely on solid fuels such as coal and wood for their daily cooking and heating needs. This action fills your home with toxic pollutants.
“I am interested in understanding how early childhood living conditions, especially indoor air pollution, can have long-term effects on cognitive health.Air pollution has been highlighted by various media outlets. lancet It is one of the modifiable risk factors for dementia. “While many studies have focused on adult exposure and urban outdoor pollution, there has been a gap in the link between childhood indoor environments and later cognitive outcomes,” said Zhong, a researcher at the Center for Population, Health and Social Inequalities at the Max Planck University of Helsinki.
Zhong wanted to see if breathing in these pollutants during the first 17 years of life had any lasting knock-on effects. From a life course perspective, early childhood experiences shape a person’s entire biological and social trajectory. Early exposure to pollution can directly interfere with brain development and cause other health problems that ultimately weaken the brain’s resilience. By viewing cognitive aging as a lifelong process, Zhong aimed to trace how early disadvantages accumulate and ultimately impact mental acuity in middle age and older age.
To investigate this, Zong analyzed data from a large, nationally representative study called the China Longitudinal Study of Health and Retirement. The final sample included 7,161 adults aged 45 and older living in China. Participants answered questions about their life history, including the type of primary cooking fuel their family used from birth until age 17. Zhong divided these people into two groups based on whether they rely on solid fuels or have access to clean energy such as electricity or natural gas.
To measure cognitive ability, participants completed several standardized mental tasks. This task assessed episodic memory, including the ability to recall recent events and information, through a memory recall test. They also measured mental health, including basic thinking skills, by asking participants to do simple calculations, redraw pictures, and accurately 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 the causal forest approach to analyze the data. It is a machine learning technique that helps scientists estimate the impact of a particular variable while taking into account the complex relationships between many different factors. The analysis controlled for several background details that could influence the results, including participants’ age, gender, marital status, and parents’ education level.
The results showed that people exposed to indoor air pollution throughout childhood tended to have significantly worse cognitive abilities later in life. This negative association was evident in both their episodic memory and mental intactness. Of the 7,161 participants, 96% grew up in households that used solid fuels. These people consistently scored lower on cognitive tests than the 4 percent who grew up using clean energy.
The study also provides evidence to explain how this early exposure influences cognitive impairment decades later. Zhong tested three potential pathways linking early life to later life: biological, psychological, and socio-economic. Data suggest that biological factors act as a bridge between early pollution exposure and subsequent cognitive decline. For example, exposure to environmental pollution during childhood was associated with higher BMI and increased physical limitations in daily activities in adulthood.
BMI is a measure of body fat based on height and weight, and higher values are associated with a variety of health problems. Limitations in daily activities refer to difficulty in performing basic self-care tasks such as dressing and bathing. Both of these biological factors represent a decline in physical health and can accelerate cognitive aging. However, levels of inflammation, measured by a blood marker called C-reactive protein, do not seem to bridge the gap between early pollution exposure and subsequent cognitive decline.
Socioeconomic factors also played a major mediating role in the study. People exposed to indoor air pollution in childhood often have less education and lower incomes as adults. These social and economic disadvantages are known to limit access to intellectual stimulation and health care and tend to accelerate cognitive aging. On the other hand, psychological factors such as experience of depressive symptoms did not show a significant associated effect in this particular analysis.
“We were somewhat surprised that this association persisted even after accounting for socio-economic factors and other early-life circumstances,” Zhong told SciPost. “Biological mediators such as BMI and limitations in activities of daily living significantly mediated this association.”
“Our analysis also revealed indirect effects through adult education and income, highlighting the role of socio-economic pathways. Children exposed to indoor air pollution are likely to have adverse life trajectories, with limited educational attainment and economic mobility, which in turn is associated with accelerated cognitive aging and increased risk of cognitive decline.”
Zhong also looked at how different groups of people are responding to the long-term effects of childhood environmental pollution. They found that men, people with a history of smoking and people who regularly consume alcohol were particularly vulnerable. These groups experienced more pronounced declines in cognitive performance if they had been exposed to indoor air pollution early in life. Dr Zhong suggests that this may be due to a combination of lifestyle choices and early environmental insults, which can combine to take a greater toll on the body over time.
“Our findings suggest that indoor air quality during early childhood is important for cognitive development and lifelong cognitive health,” Zong explained. “Improving access to clean energy (such as electricity and natural gas) in the home may help prevent cognitive decline in the first place.”
“While the effects are modest at an individual level, they are significant at a population level and highlight the importance of environmental interventions during early childhood. Given that almost 30% of the world’s population, or approximately 2.4 billion people, still cook without clean fuels, this issue is relevant not only for low- and middle-income countries, but also for populations in some high-income countries, where high energy prices after the Ukraine war have increased the use of solid fuels.”
It’s important to note that this study is observational, and while it shows an association, it cannot prove exact causation. One limitation is that participants had to recall the types of fuel their families used decades ago, which leaves room for misremembering. This is especially true when studying older adults who may already be experiencing some degree of memory loss.
Furthermore, because the majority of older adults in this sample used solid fuels, the group of unexposed people was relatively small. Although this small group represents millions of people in the general population, the imbalance makes statistical comparisons more difficult. This study focused on older people in China, so the results may not fully apply to younger generations or people living in other countries.
Zong plans to use data tracked over a longer period of time to better understand the exact cause-and-effect relationships. Future research will also test whether these findings apply to different populations around the world. By studying how early environment shapes lifelong health, scientists hope to find new ways to protect the aging brain from the beginning.
The study, “The Long Arm of Childhood: Associations between Early Childhood Indoor Air Pollution Exposure and Later Cognitive Abilities,” was authored by Xu Zong.
