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Air pollution may directly contribute to dementia

Long-term air pollution exposure may raise Alzheimer’s risk mainly through direct effects on the brain, a study of US Medicare records suggests.
The research followed more than 27.8m US Medicare recipients aged 65 and over from 2000 to 2018, comparing estimated pollution exposure with later Alzheimer’s diagnoses.
Researchers focused on PM2.5, very fine particles smaller than 2.5 micrometres that can enter the bloodstream and travel to organs including the brain.
The team, led by Dr Yanling Deng of Emory University in Atlanta, Georgia, found higher PM2.5 exposure was linked to a greater risk of Alzheimer’s disease
The association was slightly stronger among people with a history of stroke, while high blood pressure and depression appeared to make little difference.
Dr Deng said: “Overall, the findings suggest that air pollution contributes to Alzheimer’s disease mostly through direct pathways rather than through other chronic health conditions.’
“However, people with a history of stroke may be especially susceptible to the harmful effects of air pollution on brain health.”
Dr Mark Dallas, associate professor in cellular neuroscience at the University of Reading, who was not involved in the study, said: “This long-term study, which tracked 28m adults, suggests that breathing tiny particles of air pollution may slightly increase the risk of Alzheimer’s disease.
“People who have had a stroke might be somewhat more sensitive to these effects, although the increase in risk remains small.”
“Because the research relies on broad pollution estimates and medical records, there are important limitations, but the findings align with growing evidence that air pollution is a modifiable risk factor for dementia.
“Overall, the study reinforces a simple idea: what we breathe over many years can shape how our brains age.”
Matt Loxham, professor of respiratory biology and toxicology at the University of Southampton, said stroke-related damage to blood vessels in the brain could increase their “leakiness”, potentially making it easier for particles or inflammatory molecules to enter.
The blood-brain barrier is a protective lining that normally helps keep harmful substances out.
“Following a stroke, damage to the blood vessels of the brain may increase the leakiness of the vessels (termed the blood-brain barrier), which could potentially facilitate entry of particles or inflammatory molecules into the brain,” he said.
“Alternatively, it is possible that the injury caused by the stroke may render the brain more susceptible to other effects of inhaled pollution.
“However, the mechanism through which any effect of PM2.5 on Alzheimer’s disease is caused is likely to be complex and multifactorial.
“Indeed, it is notable in this study here that the majority of the association of PM2.5 with Alzheimer’s disease was seen even in individuals without previous history of stroke.
“It might be that the mechanisms through which effects occur are in place in otherwise healthy individuals, but just heightened, or acting on already injured tissue, following stroke.”
Loxham said more work was needed to establish how pollution affects the brain, whether some pollutants are more harmful than others, and who is most at risk.
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AI can predict Alzheimer’s with almost 93% accuracy, researchers say

Alzheimer’s AI can predict the disease with nearly 93 per cent accuracy using more than 800 brain scans, researchers say.
The system identified anatomical changes in the brain linked to the onset of the most common form of dementia, a condition that gradually damages memory and thinking.
The findings build on years of research suggesting AI could help spot early Alzheimer’s risk, predict disease and identify patients whose condition has not yet been diagnosed.
Benjamin Nephew, an assistant research professor at the Worcester Polytechnic Institute in Massachusetts, said: “Early diagnosis of Alzheimer’s disease can be difficult because symptoms can be mistaken for normal ageing.
“We found that machine-learning technologies, however, can analyse large amounts of data from scans to identify subtle changes and accurately predict Alzheimer’s disease and related cognitive states.”
The study used MRI scans, a type of detailed brain imaging, from 344 people aged 69 to 84.
The dataset included 281 scans showing normal mental function, 332 with mild cognitive impairment, an early stage of memory and thinking decline, and 202 with Alzheimer’s.
The scans covered 95 of the brain’s nearly 200 distinct regions and used an AI algorithm to predict patients’ health.
Being able to use AI to help diagnose Alzheimer’s earlier could give patients and doctors crucial time to prepare and potentially slow the progression of the disease.
The analysis showed that one of the top predictive factors was brain volume loss, or shrinkage, in the hippocampus, which helps form memories, the amygdala, which processes fear, and the entorhinal cortex, which helps provide a sense of time.
This pattern held across age and sex, with both men and women aged 69 to 76 showing volume loss in the right part of the hippocampus, suggesting it may be an important area for early diagnosis, the researchers noted.
However, the research also found that the way brain regions shrink differs by sex.
In females, volume loss occurred in the brain’s left middle temporal cortex, which is involved in language and visual perception. In males, it was mainly seen in the right entorhinal cortex
The researchers believe this could be linked to changes in sex hormones, including the loss of oestrogen in women and testosterone in men.
These conclusions could help improve methods of diagnosis and treatment going forward, Nephew said.
More than 7.2m Americans are living with Alzheimer’s, according to the Alzheimer’s Association.
More research is being done to reveal other impacting factors.
Nephew said: “The critical challenge in this research is to build a generalisable machine-learning model that captures the difference between healthy brains and brains from people with mild cognitive impairment or Alzheimer’s disease.”
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