Among women, exposure to polluting fuels was associated with smaller hippocampal volumes – a region critical for memory and one of the earliest to show shrinkage in Alzheimer’s disease.
Published Jul 04, 2025 | 7:00 AM ⚊ Updated Jul 04, 2025 | 7:00 AM
In rural Karnataka, nearly one in three households still depends on firewood or dung cakes for cooking.
Synopsis: A new study from the Indian Institute of Science Bengaluru has found that exposure to smoke from polluting cooking fuels is harming brain health in older adults in rural Karnataka, with women facing the most severe effects. The research, involving over 4,000 villagers in Kolar district, links household air pollution from traditional wood burning stoves to cognitive decline and reduced brain volume.
In the villages of Karnataka’s Kolar district, where traditional stoves burning wood and dung cakes remain a mainstay of daily cooking, women are facing a silent health crisis.
A new scientific study, published in The Lancet Regional Health – Southeast Asia, has found that long-term exposure to smoke from polluting cooking fuels is harming the brains of older adults in rural Karnataka – affecting memory, attention, and even altering brain structures in women.
The research, conducted by scientists at the Centre for Brain Research, Indian Institute of Science (IISc), Bengaluru, is the first in India to link household air pollution (HAP) from cooking fuels to both cognitive decline and structural changes in the brain, using MRI scans.
The study focused on over 4,145 people aged 45 and above from the villages of Srinivaspura, a rural taluk in Kolar district. Most participants belong to farming communities and have limited formal education.
Researchers assessed their cognitive performance through a series of computer-based and language-adapted tests. Around 1,000 participants also underwent MRI scans to examine changes in brain structures.
Out of the 8,059 individuals initially enrolled, 4,145 had complete cognitive data and were included in the final analysis. The average age of the study population was 57.2 years, with 43.66 percent being women.
Participants were grouped based on the type of cooking fuel used: 2,480 (59.83 percent) used only clean cooking fuels, 1,585 (38.23 percent) used a mix of clean and polluting fuels, and 80 (1.93 percent) relied solely on polluting fuels such as firewood, cow dung, or kerosene.
What the researchers found was both stark and concerning. People using only polluting fuels scored significantly lower on tests assessing memory, visual processing, and decision-making.
Even those using a combination of clean and polluting fuels performed worse than those who used only clean options like LPG or electricity.
The study revealed significant cognitive impairments across a range of brain functions. Participants who used only polluting cooking fuels scored 0.28 standard deviations lower in overall cognitive performance compared to those using clean cooking technologies.
They also performed 0.28 standard deviations worse in geometric figure matching tests, which assess visuospatial ability, and 0.25 standard deviations lower in semantic association tests, which measure executive function.
Those using at least one polluting cooking technology scored 0.10 standard deviations lower on the Hindi Mental State Examination (HMSE) – a widely used screening tool for dementia.
An age-stratified analysis showed that participants under 60 using polluting fuels scored 0.12 standard deviations lower on HMSE tests, while those aged 60 and above scored 0.12 standard deviations lower on visuospatial ability tests.
The study’s most concerning findings emerged when the data was broken down by gender. Among women, exposure to polluting fuels was associated with smaller hippocampal volumes – a region critical for memory and one of the earliest to show shrinkage in Alzheimer’s disease.
Sex-stratified analysis found that women using polluting cooking fuels had HMSE scores 0.11 standard deviations lower than those using clean fuels. No such association was observed in men.
MRI data further confirmed the link: among women, those using polluting fuels had hippocampal volumes 0.18 standard deviations smaller than those using clean cooking fuels.
The hippocampus, a seahorse-shaped structure deep in the brain, plays a key role in learning and memory and is particularly vulnerable in neurodegenerative conditions like Alzheimer’s.
In rural Karnataka, despite years of clean fuel initiatives, nearly one in three households (30.7 percent) still depends on traditional biomass – such as firewood or dung cakes – for cooking, according to the National Family Health Survey.
Burning these fuels in open stoves or poorly ventilated kitchens releases harmful gases and fine particles that not only damage the lungs, but now appear to affect the brain as well.
The study’s discussion section outlines how cooking smoke may impact brain health.
“When solid fuels are burned indoors for cooking, especially in poorly ventilated spaces, air pollutants like oxides of carbon, nitrogen, sulphur, heavy metals, volatile organic compounds, and suspended particulate matter are released,” the researchers explain.
“The primary mechanisms may be related to inflammation and oxidative stress, wherein ultrafine air pollutants affect the brain directly by entering the brain through the olfactory bulb or by crossing the blood–brain barrier. Air pollutants are also postulated to indirectly affect the brain by inducing systemic inflammation, which may reach the brain via circulating cytokines.”
India’s population is ageing rapidly. By 2050, nearly 20 percent of the country will be over the age of 60, raising the risk of a surge in dementia cases.
Yet, most studies on dementia have focused on genetics or conditions such as diabetes and hypertension. This study marks a critical shift in understanding environmental risk factors.
The researchers point out that “HAP also significantly contributes to India’s overall disease burden, especially in rural areas, wherein agrarian populations primarily rely on cheap, polluting fuels like cow dung cakes and crop residue.
India faces a significant risk of dementia due to an increase in the proportion of ageing populations, and the dependence on polluting cooking technology is more pervasive among rural populations.”
The study’s findings carry serious public health implications. Despite government schemes like the Pradhan Mantri Ujjwala Yojana, which aimed to provide free LPG connections to low-income households, adoption in rural areas remains limited.
Many families revert to biomass fuels due to high refill costs, supply issues, or cultural preferences.
“Despite initiatives like the Prime Minister Ujjwala Yojana, which was implemented in 2016 to replace the reliance of adult women from economically necessitous households on polluting cooking fuels with LPG, problems like regional disparities in the programme implementation and lack of complete and permanent adoption of LPG as the only cooking fuel due to factors like prohibitive cost of refills, continue to persist,” the study notes.
The authors stress that “recognising HAP as a risk factor for dementia could drive improved implementation and adoption of such initiatives. There is an urgent need for a complete and sustained switch to cleaner cooking fuels and technology.”
They recommend going beyond traditional LPG distribution, advocating for alternative, locally adapted solutions.
As they note, “clean fuel stacking-based strategies should also be planned and implemented in rural areas of India, wherein, alongside LPG, rural households can also rely on community biogas plants and solar electric mini grids to offer a sustained supply of affordable clean fuels for cooking.”
