Air pollution raises risk of Alzheimer's in elderly women

Elderly women exposed to high levels of air pollution may be at up to double the risk of Alzheimer’s, study of brain shrinkage suggests

  • Researchers studied the changes in brain volume of 712 women over five years
  • They found air pollution increases the risk of Alzheimer’s-related brain shrinkage
  • The team just looked at women, who are at a higher risk of Alzheimer’s than men
  • The study also only considered regional air pollution — not traffic emissions

Long-term exposure to high air pollution levels may raise older women’s risk of Alzheimer’s-related brain shrinkage by up to double, a study has suggested.

Researchers from the US studied the changes in brain volume of 712 senior women and compared this with their estimated annual level of air pollution exposure.

Fine particle pollution is comprised of tiny bits of smoke, dust and other chemical substances suspended in the air, the breathing in of which causes health issues.

The team found that the more air pollution women were exposed to over five-year-period, the greater the shrinking of the brain areas vulnerable to Alzheimer’s. 

In fact, women exposed to the highest levels seen in the study — 19 micrograms per cubic metre (μg/m³) — were at twice the risk of those with the lowest exposure.

The least exposed participants received only 7 μg/m³ on average — and every 3 micrograms per cubic metre increased the risk of Alzheimer’s by 24 per cent.

Women are disproportionally more affected by Alzheimer’s compared with men. 

The study — based on data collected by the Women’s Health Initiative — may not necessarily translate to men or younger women, the researchers cautioned.

In addition, the team only considered regional air pollution and did not factor in other sources — such as traffic emissions that come from busy roads.

Long-term exposure to high air pollution levels may raise older women’s risk of Alzheimer’s-related brain shrinkage by up to double, a study has suggested

‘Smaller brain volume is a known risk factor for dementia and Alzheimer’s disease, but whether air pollution alters brain structure is still being researched,’ said paper author Diana Younan of the University of Southern California in Los Angeles.

‘Our study found that women in their 70s and 80s who were exposed to the higher levels of air pollution had an increased risk of brain changes linked to Alzheimer’s disease over five years,’ she added.

‘Our research suggests these toxins may disrupt brain structure or connections in the brain’s nerve cell network, contributing to the progression toward the disease.’ 

In their study, Dr Younan and colleagues recruited 712 women aged 78 or over — none of whom had dementia when the study began — and took MRI scans of their brains both at the study’s start and again five years later.

Each participant provided the researchers with access to their health records — along with information on their ethnicity/race, educational background, employment records, typical levels of physical activity and alcohol/tobacco habits.

The researchers used each woman’s residential address to estimate their average exposure to air pollution in the three years preceding their first MRI scan — from which they divided the subjects into four equal groups

Researchers used the residential addresses of each participant to determine their average exposures to air pollution in the three years before the first MRI scan. They then divided participants into four equal groups based on this exposure.

For example, the lowest group included those exposed to an average of 7–10 micrograms of fine particle pollution per cubic metre of air — while the highest group was instead exposed to 13–19 micrograms per cubic metre.

In the US, where the study was conducted, the Environmental Pollution Agency considers safe an average yearly exposure of up to 12 micrograms per cubic metre.

Fine particle pollution is comprised of tiny bits of smoke, dust and other chemical substances suspended in the air, the breathing in of which causes health issues (stock image)

Using a machine learning tool trained to identify patterns of brain shrinkage — such that is indicative of Alzheimer’s disease — the researchers assigned each MRI with a score based on how similar the scans were to those of people with the disease.

The resulting scores ranged from zero to one — with the higher the score, the greater the Alzheimer’s-related changes in brain volume .

The team found that the women’s score averaged at 0.28 at the start of the study, but had increased to 0.44 five years later. 

Moreover, the researchers noted, for every 3 micrograms per cubic metre increase of air pollution exposure there was an average score increase of 0.03 over the five-year period — the equivalent of a 24 per cent higher risk of Alzheimer’s.

This increase in risk with higher pollution levels was found to hold even once the team had adjusted for other factors that could contribute to brain shrinkage — which include age, education, employment, heart health and physical activity. 

‘Our findings have important public health implications,’ added Dr Younan.

‘Not only did we find brain shrinkage in women exposed to higher levels of air pollution, we also found it in women exposed to air pollution levels lower than those the Environmental Protection Agency considers safe.’

‘While more research is needed, federal efforts to tighten air pollution exposure standards in the future may help reduce the risk of Alzheimer’s disease in our older populations,’ she concluded.

The full findings of the study were published in the journal Neurology: Clinical Practice.

Revealed: MailOnline dissects the impact greenhouse gases have on the planet – and what is being done to stop air pollution


Carbon dioxide

Carbon dioxide (CO2) is one of the biggest contributors to global warming. After the gas is released into the atmosphere it stays there, making it difficult for heat to escape – and warming up the planet in the process. 

It is primarily released from burning fossil fuels such as coal, oil and gas, as well as cement production. 

The average monthly concentration of CO2 in the Earth’s atmosphere, as of April 2019, is 413 parts per million (ppm). Before the Industrial Revolution, the concentration was just 280 ppm. 

CO2 concentration has fluctuated over the last 800,000 years between 180 to 280ppm, but has been vastly accelerated by pollution caused by humans. 

Nitrogen dioxide 

The gas nitrogen dioxide (NO2) comes from burning fossil fuels, car exhaust emissions and the use of nitrogen-based fertilisers used in agriculture.

Although there is far less NO2 in the atmosphere than CO2, it is between 200 and 300 times more effective at trapping heat.

Sulfur dioxide 

Sulfur dioxide (SO2) also primarily comes from fossil fuel burning, but can also be released from car exhausts.

SO2 can react with water, oxygen and other chemicals in the atmosphere to cause acid rain. 

Carbon monoxide 

Carbon monoxide (CO) is an indirect greenhouse gas as it reacts with hydroxyl radicals, removing them. Hydroxyl radicals reduce the lifetime of carbon dioxide and other greenhouse gases. 


What is particulate matter?

Particulate matter refers to tiny parts of solids or liquid materials in the air. 

Some are visible, such as dust, whereas others cannot be seen by the naked eye. 

Materials such as metals, microplastics, soil and chemicals can be in particulate matter.

Particulate matter (or PM) is described in micrometres. The two main ones mentioned in reports and studies are PM10 (less than 10 micrometres) and PM2.5 (less than 2.5 micrometres).

Air pollution comes from burning fossil fuels, cars, cement making and agriculture 

Scientists measure the rate of particulates in the air by cubic metre.

Particulate matter is sent into the air by a number of processes including burning fossil fuels, driving cars and steel making.

Why are particulates dangerous?

Particulates are dangerous because those less than 10 micrometres in diameter can get deep into your lungs, or even pass into your bloodstream. Particulates are found in higher concentrations in urban areas, particularly along main roads. 

Health impact

What sort of health problems can pollution cause?

According to the World Health Organization, a third of deaths from stroke, lung cancer and heart disease can be linked to air pollution. 

Some of the effects of air pollution on the body are not understood, but pollution may increase inflammation which narrows the arteries leading to heart attacks or strokes. 

As well as this, almost one in 10 lung cancer cases in the UK are caused by air pollution. 

Particulates find their way into the lungs and get lodged there, causing inflammation and damage. As well as this, some chemicals in particulates that make their way into the body can cause cancer. 

Deaths from pollution 

Around seven million people die prematurely because of air pollution every year. Pollution can cause a number of issues including asthma attacks, strokes, various cancers and cardiovascular problems. 


Asthma triggers

Air pollution can cause problems for asthma sufferers for a number of reasons. Pollutants in traffic fumes can irritate the airways, and particulates can get into your lungs and throat and make these areas inflamed. 

Problems in pregnancy 

Women exposed to air pollution before getting pregnant are nearly 20 per cent more likely to have babies with birth defects, research suggested in January 2018.

Living within 3.1 miles (5km) of a highly-polluted area one month before conceiving makes women more likely to give birth to babies with defects such as cleft palates or lips, a study by University of Cincinnati found.

For every 0.01mg/m3 increase in fine air particles, birth defects rise by 19 per cent, the research adds. 

Previous research suggests this causes birth defects as a result of women suffering inflammation and ‘internal stress’. 

What is being done to tackle air pollution? 

Paris agreement on climate change

The Paris Agreement, which was first signed in 2015, is an international agreement to control and limit climate change. 

It hopes to hold the increase in the global average temperature to below 2°C (3.6ºF) ‘and to pursue efforts to limit the temperature increase to 1.5°C (2.7°F)’.

Carbon neutral by 2050 

The UK government has announced plans to make the country carbon neutral by 2050. 

They plan to do this by planting more trees and by installing ‘carbon capture’ technology at the source of the pollution.

Some critics are worried that this first option will be used by the government to export its carbon offsetting to other countries.

International carbon credits let nations continue emitting carbon while paying for trees to be planted elsewhere, balancing out their emissions.

No new petrol or diesel vehicles by 2040

In 2017, the UK government announced the sale of new petrol and diesel cars would be banned by 2040.  

However,  MPs on the climate change committee have urged the government to bring the ban forward to 2030, as by then they will have an equivalent range and price.

The Paris Agreement, which was first signed in 2015, is an international agreement to control and limit climate change. Pictured: air pollution over Paris in 2019.

Norway’s electric car subsidies

The speedy electrification of Norway’s automotive fleet is attributed mainly to generous state subsidies. Electric cars are almost entirely exempt from the heavy taxes imposed on petrol and diesel cars, which makes them competitively priced.

A VW Golf with a standard combustion engine costs nearly 334,000 kroner (34,500 euros, $38,600), while its electric cousin the e-Golf costs 326,000 kroner thanks to a lower tax quotient. 

Criticisms of inaction on climate change

The Committee on Climate Change (CCC) has said there is a ‘shocking’ lack of Government preparation for the risks to the country from climate change. 

The committee assessed 33 areas where the risks of climate change had to be addressed – from flood resilience of properties to impacts on farmland and supply chains – and found no real progress in any of them.

The UK is not prepared for 2°C of warming, the level at which countries have pledged to curb temperature rises, let alone a 4°C rise, which is possible if greenhouse gases are not cut globally, the committee said.

It added that cities need more green spaces to stop the urban ‘heat island’ effect, and to prevent floods by soaking up heavy rainfall. 

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