Does air pollution cause Alzheimer's disease?
Does air pollution cause Alzheimer's disease?
Hello everyone,
According to the World Health Organisation (WHO), air pollution is one of the greatest environmental risks to health and in 2019, 99% of the world’s population lived in places where the WHO air quality guidelines were not met.
Air pollution is known to be linked to lung disorders, but could it also harm our brains? We asked 6 experts in epidemiology, biostatistics and neurology, ‘Does air pollution cause Alzheimer's disease?’, this is what they said…
EXPERT CONSENSUS
Does air pollution cause Alzheimer's disease?
4 out of 6 experts says ‘likely’
What is Alzheimer’s disease?
Alzheimer's disease is a brain disorder that causes a gradual decline in cognitive function. Alzheimer’s disease is the most common form of dementia, an umbrella term which refers to memory loss and cognitive decline. Over 55 million people worldwide have dementia, and 60-70% of those people have Alzheimer’s disease.
What is air pollution and where does it come from?
Air pollution is the chemicals or particles in the air that can harm plants and animals (including humans). Air pollution can come from human sources such as emissions from factories, cars or planes, or natural sources such as wildfires or volcanos. Air pollution can be worsened by heat or mountains which prevent air movement.
Dr Eirini Dimakakou, an expert in epidemiology and biostatistics from Heriot Watt University in Scotland, says “Particulate matter (PM), also known as particulate air pollution, is a complex mixture of extremely small particles and liquid droplets that are in the air of our cities. Once these particles are inhaled, they can cause serious health effects. Particles that are very small in diameter cause the greatest problems, because they can get very deep into the lungs, and they may even get into the bloodstream or the brain. Particulate matter comes from both human and natural sources. Soot from diesel vehicles, smoke from fires and wind-blown dust are all sources of airborne particulate matter.”
What are the dangers of air pollution?
Dr Dimakakou, says “Exposure to air pollution is a particular concern to the public. In Britain, the 1952 ‘London Smog’ heightened public awareness of the problem because of the increased mortality and morbidity reported soon after the event.” The ‘Great Smog of London’ was caused by a combination of people burning coal in their homes to keep warm and smog-forming weather conditions, and it was estimated to result in the death of at least 4,000 people.
Dr Dimakakou says “It is now widely accepted that exposure to air pollution may cause or exacerbate allergic respiratory diseases (e.g., asthma), chronic obstructive pulmonary disease, pneumonia, lung cancer and cardiovascular disease. More recently, evidence has emerged from epidemiological and experimental laboratory studies that long-term exposure to particulate air pollution may be associated with dementia.”
Professor Paul Ernsberger, an expert in pharmacology from Case Western Reserve University in the USA, explains how air pollution can affect our health, saying “Very small particles can enter the blood stream within the alveoli of the lung. From there they can reach the brain and other organs. Rates of lung, heart and neurological diseases can be linked to exposure to fine particulates smaller than 2.5 microns in diameter.”
Does air pollution cause Alzheimer's disease?
Dr Tia Louise Cummins, an expert in neuroscience from the Florey Institute of Neuroscience and Mental Health in Australia, says “Scientists are still unsure of the exact cause(s) of Alzheimer's, however it is likely that a number of factors are involved. Air pollution may be associated with Alzheimer's, but it is unlikely that it is the ‘cause’. Many lifestyle and medical variables are associated with Alzheimers, but we can not deduce the finite cause just yet.”
Dr Tim Wilkinson, an expert in neurology and Alzheimer’s disease from Edinburgh University in Scotland, highlights a review paper that examined the results of 9 research articles looking at the relationship between air pollution and brain health. He summarises the conclusions of the review as
“There is now ample evidence that links air pollution to poor brain health
We don't understand when in the life course air pollution has the most impact (i.e. is it worse if exposed to air pollution in childhood, midlife etc)
We don't understand whether it affects one particular subtype of dementia (e.g. Alzheimer's disease, vascular dementia) compared to others.”
Dr Dimakakou says “Human epidemiological evidence suggests that long-term exposure to fine particulate air pollution may be a risk factor for neurodegenerative diseases. The mechanisms underlying this are currently unknown, but it may involve the particles moving from the inhaled air to the brain or the release of inflammatory chemicals from the lung, which may indirectly cause damage in the brain.”
Dr Dimakakou goes on to say that “It is not absolutely clear whether particulate air pollution causes dementia, although exposure to air pollution may contribute to the initiation of disease or accelerate disease development. Is particulate air pollution an important cause or just another cause? It’s known that small air pollution particles can enter the brain and the research shows a fairly consistent evidence of a link between air pollution and neurodegenerative diseases, but just not quite sufficient to provide unequivocal scientific proof. There are so many questions still unanswered, which definitely suggests a need for further research in this field.”
Professor Ying Zhang, an expert in epidemiology from Sydney University in Australia, summarises by saying that air pollution “may not be a direct cause of Alzheimer's disease but an epidemiological risk factor that could contribute to the development of the disease.”
The takeaway:
Air pollution may be linked to Alzheimer’s disease, but more research is needed to confirm this.
May the facts be with you!
Eva
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