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An analysis of studies incorporating data from almost 30 million people has highlighted the role that air pollution – including that coming from car exhaust emissions – plays in increased risk of dementia.

Dementias such as Alzheimer's disease are estimated to affect more than 57.4 million people worldwide, a number that is expected to almost triple to 152.8 million cases by 2050. The impacts on the individuals, families and caregivers and society at large are immense.

While there are some indications that the prevalence of dementia is decreasing in Europe and North America, suggesting that it may be possible to reduce the risk of the disease at a population level, elsewhere the picture is less promising.

Air pollution has recently been identified as a risk factor for dementia, with several studies pointing the finger at a number of pollutants. However, the strength of evidence and ability to determine a causal effect has been varied.

In a paper published today in The Lancet Planetary Health, a team led by researchers at the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge, carried out a systematic review and meta-analysis of existing scientific literature to examine this link further. This approach allowed them to bring together studies that on their own may not provide sufficient evidence, and which sometimes disagree with each other, to provide more robust overarching conclusions.

In total, the researchers included 51 studies, including data from more than 29 million participants who had been exposed to air pollutants for at least one year, mostly from high-income countries. Of these, 34 papers were included in the meta-analysis: 15 originated in North America, 10 in Europe, seven in Asia, and two in Australia.

The researchers found a positive and statistically-significant association between three types of air pollutant and dementia. These were:

Particulate matter with a diameter of 2.5 microns or less (PM2.5), a pollutant made up of tiny particles small enough that they can be inhaled deep into the lungs. These particles come from several sources, including vehicle emissions, power plants, industrial processes, wood burning stoves and fireplaces, and construction dust. They also form in the atmosphere because of complex chemical reactions involving other pollutants such as sulphur dioxide and nitrogen oxides. The particles can stay in the air for a long time and travel a long way from where they were produced.

Nitrogen dioxide (NO2), one of the key pollutants that arise from burning fossil fuels. It is found in vehicle exhaust, especially diesel exhaust, and industrial emissions, as well as those from gas stoves and heaters. Exposure to high concentrations of nitrogen dioxide can irritate the respiratory system, worsening and inducing conditions like asthma and reducing lung function.

Soot from sources such as vehicle exhaust emissions and burning wood. It can trap heat and affect the climate. When inhaled, it can penetrate deep into the lungs, aggravating respiratory diseases and increasing the risk of heart problems.

According to the researchers, for every 10 micrograms per cubic meter (μg/m³) of PM2.5, an individual’s relative risk of dementia would increase by 17%. The average roadside measurement for PM2.5 in Central London in 2023 was 10 μg/m³.

For every 10 μg/m3 of NO2, the relative risk increased by 3%. The average roadside measurement for NO2 in Central London in 2023 was 33 µg/m³.

For each 1 μg/m³ of soot as found in PM2.5, the relative risk increased by 13%. Across the UK, annual mean soot concentrations measured at select roadside locations in 2023 were 0.93 μg/m³ in London, 1.51 μg/m³ in Birmingham and 0.65 μg/m³ in Glasgow.

Senior author Dr Haneen Khreis from the MRC Epidemiology Unit said: “Epidemiological evidence plays a crucial role in allowing us to determine whether or not air pollution increases the risk of dementia and by how much. Our work provides further evidence to support the observation that long-term exposure to outdoor air pollution is a risk factor for the onset of dementia in previously healthy adults.

“Tackling air pollution can deliver long-term health, social, climate, and economic benefits. It can reduce the immense burden on patients, families, and caregivers, while easing pressure on overstretched healthcare systems.”

Several mechanisms have been proposed to explain how air pollution may cause dementia, primarily involving inflammation in the brain and oxidative stress (a chemical process in the body that can cause damage to cells, proteins, and DNA). Both oxidative stress and inflammation play a well-established role in the onset and progression of dementia. Air pollution is thought to trigger these processes through direct entry to the brain or via the same mechanisms underlying lung and cardiovascular diseases. Air pollution can also enter circulation from the lungs and travel to solid organs, initiating local and wide-spread inflammation.

The researchers point out that the majority of people included in the published studies were white and living in high-income countries, even though marginalised groups tend to have a higher exposure to air pollution. Given that studies have suggested that reducing air pollution exposure appears to be more beneficial at reducing the risk of early death for marginalised groups, they call for future work to urgently ensure better and more adequate representation across ethnicities and low- and middle-income countries and communities.

Joint first author Clare Rogowski, also from the MRC Epidemiology Unit, said: “Efforts to reduce exposure to these key pollutants are likely to help reduce the burden of dementia on society. Stricter limits for several pollutants are likely to be necessary targeting major contributors such as the transport and industry sectors. Given the extent of air pollution, there is an urgent need for regional, national, and international policy interventions to combat air pollution equitably.”

Further analysis revealed that while exposure to these pollutants increased the risk of Alzheimer's disease, the effect seemed stronger for vascular dementia, a type of dementia caused by reduced blood flow to the brain. Around 180,000 people in the UK are thought to be affected by this type of dementia. However, as there were only a small number of studies that examined this difference, the researchers did not class it as statistically significant.

Joint first author Dr Christiaan Bredell from the University of Cambridge and North West Anglia NHS Foundation Trust said: “These findings underscore the need for an interdisciplinary approach to dementia prevention. Preventing dementia is not just the responsibility of healthcare: this study strengthens the case that urban planning, transport policy, and environmental regulation all have a significant role to play.”

The research was funded by the European Research Council under the Horizon 2020 research and innovation programme and from the European Union’s Horizon Europe Framework Programme.

Reference

Best Rogowski, CB, & Bredell, C et al. Long-term Air Pollution Exposure and Incident Dementia: A Systematic Review and Meta-Analysis. Lancet Planetary Health; 24 July 2025; DOI: 10.1016/S2542-5196(25)00118-4

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https://www.iea.org/reports/energy-and-ai/ai-and-climate-change

And AI companies should have societal stigma of oil and mining companies

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"To date, most genetic data suggests that modern humans evolved in Africa 250,000 years ago, stayed put for the next 200,000 years, and then decided to disperse out of Africa 50,000 years ago and go on to people the rest of the world," said Akey.

"Our models show that there wasn't a long period of stasis, but that shortly after modern humans arose, we've been migrating out of Africa and coming back to Africa, too," he said. "To me, this story is about dispersal, that modern humans have been moving around and encountering Neanderthals and Denisovans much more than we previously recognized."

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For infants (<1 year old)

Between 2007 to 2022, infants were 1.78 (95% CI, 1.78-1.79) times more likely to die in the US than in the OECD18.

The 2 causes of death with the largest net difference between the US and OECD18 were prematurity (RR, 2.22 [95% CI, 2.20-2.24]) and sudden unexpected infant death (RR, 2.39 [95% CI, 2.35-2.43]).

For kids aged 1 to 19 years old

Between 2007 to 2022, 1- to 19-year olds were 1.80 (95% CI, 1.80-1.80) times more likely to die in the US than in the OECD18.

The 2 causes of death with the largest net difference between the US and OECD18 were firearm-related incidents (RR, 15.34 [95% CI, 14.89-15.80]) and motor vehicle crashes (RR, 2.45 [95% CI, 2.42-2.48]).

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Earth is expected to spin more quickly in the coming weeks, making some of our days unusually short. On July 9, July 22 and Aug. 5, the position of the moon is expected to affect Earth's rotation so that each day is between 1.3 and 1.51 milliseconds shorter than normal.

I guess I need to cancel my plans today, not enough time in the day.

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spoilerThe herbicide ingredient used to replace glyphosate in Roundup and other weedkiller products can kill gut bacteria and damage organs in multiple ways, new research shows.

The ingredient, diquat, is widely employed in the US as a weedkiller in vineyards and orchards, and is increasingly sprayed elsewhere as the use of controversial herbicide substances such as glyphosate and paraquat drops in the US.

But the new piece of data suggests diquat is more toxic than glyphosate, and the substance is banned over its risks in the UK, EU, China and many other countries. Still, the EPA has resisted calls for a ban, and Roundup formulas with the ingredient hit the shelves last year. Foam washes up from a body of water onto sandy ground with scrubby plants. ‘We thought we’d got the numbers wrong’: how a pristine lake came to have the highest levels of ‘forever chemicals’ on record Read more

“From a human health perspective, this stuff is quite a bit nastier than glyphosate so we’re seeing a regrettable substitution, and the ineffective regulatory structure is allowing it,” said Nathan Donley, science director with the Center For Biological Diversity, which advocates for stricter pesticide regulations but was not involved in the new research. “Regrettable substitution” is a scientific term used to describe the replacement of a toxic substance in a consumer product with an ingredient that is also toxic.

Diquat is also thought to be a neurotoxin, carcinogen and linked to Parkinson’s disease. An October analysis of EPA data by the Friends of the Earth non-profit found it is about 200 times more toxic than glyphosate in terms of chronic exposure.

Bayer, which makes Roundup, faced nearly 175,000 lawsuits alleging that the product’s users were harmed by the product. Bayer, which bought Monsanto in 2018, reformulated Roundup after the International Agency for Research on Cancer classified glyphosate as a possible carcinogen.

The new review of scientific literature in part focuses on the multiple ways in which diquat damages organs and gut bacteria, including by reducing the level of proteins that are key pieces of the gut lining. The weakening can allow toxins and pathogens to move from the stomach into the bloodstream, and trigger inflammation in the intestines and throughout the body. Meanwhile, diquat can inhibit the production of beneficial bacteria that maintain the gut lining.

Damage to the lining also inhibits the absorption of nutrients and energy metabolism, the authors said.

The research further scrutinizes how the substance harms the kidneys, lungs and liver. Diquat “causes irreversible structural and functional damage to the kidneys” because it can destroy kidney cells’ membranes and interfere with cell signals. The effects on the liver are similar, and the ingredient causes the production of proteins that inflame the organ.

Meanwhile, it seems to attack the lungs by triggering inflammation that damages the organ’s tissue. More broadly, the inflammation caused by diquat may cause multiple organ dysfunction syndrome, a scenario in which organ systems begin to fail.

The authors note that many of the studies are on rodents and more research on low, long-term exposure is needed. Bayer did not immediately respond to a request for comment.

Despite the risks amid a rise in diquat’s use, the EPA is not reviewing the chemical, and even non-profits that push for tighter pesticide regulations have largely focused their attention elsewhere.

Donley said that was in part because US pesticide regulations are so weak that advocates are tied up with battles over ingredients like glyphosate, paraquat and chlorpyrifos – substances that are banned elsewhere but still widely used here. Diquat is “overshadowed” by those ingredients.

“Other countries have banned diquat, but in the US we’re still fighting the fights that Europe won 20 years ago,” Donley said. “It hasn’t gotten to the radar of most groups and that really says a lot about the sad and sorry state of pesticides in the US.”

Some advocates have accused the EPA of being captured by industry, and Donley said US pesticide laws were so weak that it was difficult for the agency to ban ingredients, even if the will exists. For example, the agency banned chlorpyrifos in 2022, but a court overturned the decision after industry sued.

Moreover, the EPA’s pesticides office seems to have a philosophy that states that toxic pesticides are a “necessary evil”, Donley said.

“When you approach an issue from that lens there’s only so much you will do,” he said.

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Today I learned polygamy is technically not gender equal

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