Is air pollution causing us to lose our sense of smell?

Our sense of smell is one of our richest and wide-ranging windows into the world around us, but a threat in the air we breathe may be eroding our olfactory powers. For many people, a bout of Covid-19 gave a first taste (or rather a lack of it) of what it is like to lose their sense of smell. Known as "anosmia", loss of smell can have a substantial effect on our overall wellbeing and quality of life. But while a sudden respiratory infection might lead to a temporary loss of this important sense, your sense of smell may well have been gradually eroding away for years due to something else – air pollution. Exposure to PM2.5 – the collective name for small airborne pollution particles, largely from the combustion of fuels in vehicles, power stations and our homes – has previously been linked with "olfactory dysfunction", but typically only in occupational or industrial settings. But new research is now starting to reveal the true scale – and the potential damage caused by – the pollution we breathe in every day. And their findings have relevance for us all. On the underside of our brains, just above our nasal cavities, lies the olfactory bulb. This sensitive bit of tissue bristles with nerve endings and is essential for the enormously varied picture of the world we get from our sense of smell. It's also our first line of defence against viruses and pollutants entering the brain. But, with repeated exposure, these defences slowly get worn down – or breached. "Our data show there's a 1.6 to 1.7-fold increased [risk of] developing anosmia with sustained particulate pollution," says Murugappan Ramanathan Jr, a rhinologist at the Johns Hopkins School of Medicine, Baltimore. He has become one of the few experts in this field after he started to wonder if there was a link between the large numbers of patients he was seeing with anosmia and the environmental conditions where they lived. The simple question he wanted to answer was this: were a disproportionate number of anosmia patients living in areas of higher PM2.5 pollution? Until recently, the little scientific research on this topic included one Mexican study in 2006, which used strong coffee and orange odours to show that residents of Mexico City – which often struggles with air pollution – tended to have a poorer sense of smell on average than people living in rural areas of the country. With the help of colleagues – including environmental epidemiologist Zhenyu Zhang who created a map of historic air pollution data in the Baltimore area – Ramanathan set up a case-control study of data from 2,690 patients who had attended Johns Hopkins Hospital over a four year period. Around 20% had anosmia and most didn't smoke – a habit that is known to affect the sense of smell. Sure enough, the levels of PM2.5 were found to be "significantly higher" in the neighbourhoods where patients with anosmia lived compared to healthy control participants. Even when adjusted for age, sex, race/ethnicity, body mass index, alcohol or tobacco use, the findings came up the same: "Even small increases in ambient PM2.5 exposure may be associated with anosmia". The finding has been echoed in other parts of the world in studies published this year. One recent study in Brescia, northern Italy, for example, found the noses of teenagers and young adults became less sensitive to smells the more nitrogen dioxide – another pollutant produced when fossil fuels are burned, in particular from vehicle engines – they were exposed to. Another year-long study in São Paulo, Brazil, also indicated that people living in areas with higher particulate pollution had an impaired sense of smell. But exactly how is pollution wrecking our ability to smell? According to Ramanathan there are two potential routes. One is that some of the pollution particles are passing through the olfactory bulb and getting directly into the brain, causing inflammation. "Olfactory nerves are in the brain but they have little holes at the base of skull where little fibres go into the nose, [looking] almost like little pieces of angel hair pasta," says Ramanathan. "They are exposed." In 2016, a team of British researchers found tiny metal particles in human brain tissue that appeared to have passed through the olfactory bulb. Barbara Maher, a professor of environmental science at Lancaster University in the UK who led the study, said at the time that the particles were "strikingly similar" to those found in airborne pollution next to busy roads (domestic fireplaces and log stoves were another possible source). Maher's study suggests that these nanoscale metal particles could, once in the brain, become toxic, contributing to oxidative brain damage that damages the neural pathways, although it still remains a theory. The other potential mechanism, says Ramanathan, may not even require pollution particles getting into the brain. By hitting the olfactory bulb on an almost daily basis, they cause inflammation and damage to the nerves directly, slowly wearing them away. Think of it almost like coastal erosion, where sandy, salty waves eat away at the shoreline; substitute waves with pollution-filled air, and shoreline with our nasal nerves. ‟ Modern combustion methods can create nanoparticles so fine that they are small enough to directly enter our bloodstream and brain tissue Unsurprisingly then, anosmia disproportionately affects older people, whose noses have been assaulted by air pollution for longer. More surprisingly, none of the Johns Hopkins patients lived in areas with excessively high air pollution – many lived in leafy areas of Maryland, and none were from pollution hotspots. It suggests that even low levels of air pollution could cause problems over a long enough period. A similar recent study has separately been carried out by the Aging Research Center at the Karolinska Institute, in Stockholm. Postdoctoral researcher Ingrid Ekström was puzzled by findings from the early 2000s that showed more than 5.8% of adults in Sweden had anosmia, and 19.1% had some form of olfactory dysfunction. Knowing that anosmia rates were higher in older people, Ekström and colleagues designed a study using 3,363 patients aged 60 and over. Using strongly scented "sniffing sticks" of 16 common household smells, participants received a score depending on the number they could correctly identify. As with the Baltimore study, the participants' home addresses were mapped and analysed according to municipal air pollution readings. And as in Baltimore, there was a strong correlation between higher pollution levels and poorer smelling ability.  "They have been subjected to pollution throughout their lives," says Ekström. "We don't know exactly when their olfactory impairments started to decline.” But she is “confident” that long-term exposure to pollution was the cause, even at low levels. In 2021, The World Health Organization (WHO) changed its health-based guidelines for a maximum annual average exposure to PM2.5, reducing it from 10 to 5 micrograms per cubic metre (µg/m3). Stockholm, Sweden's capital, is one of the few major cities in the world that manages to stay below this level with an annual average of 4.2µg/m3. By comparison, Islamabad, in Pakistan, has an annual average PM2.5 levels of 41.1µg/m3 while it is 42.3µg/m3 in Bloemfontein, South Africa. This arguably makes the Stockholm findings even more relevant – if even Stockholm residents are having their senses eroded by low levels of pollution, then how much worse will it be in regions with high levels? It is also a reminder of how highly localised pollution can be, both outdoors and indoors. People's cooking methods and heating choices may be exposing them to higher levels than their neighbours. (Listen to learn how effective air purifiers are.) Meanwhile modern combustion methods from vehicle engines to the latest 'eco' wood stoves can create nanoparticles so fine that they barely register on PM2.5 readings, but are small enough to directly enter our bloodstream and brain tissue. Air pollution is known to cause a quarter of all deaths from heart disease and stroke, and nearly half of all deaths from lung disease. By comparison, perhaps, our sense of smell seems low down the list of concerns. But both Ramanathan and Ekström warn that we underestimate the importance of smell at our peril. Ekström's research speciality is dementia. And anosmia may be an early warning sign. "With dementia and especially with Alzheimer's Disease, we assume that [the] disease progression is actually starting several decades before we can see the first symptoms," says Ekström.  Anosmia is one of the first symptoms. By the time Alzheimer's is diagnosed, "almost 90% of patients have anosmia", says Ekström. The exact link remains unknown, but one theory is that "environmental toxins enter the central nervous system via the olfactory bulb and cause damage, triggering this cascade effect that may ultimately lead to neuro-degeneration". The Maher Lancaster study, for example, found that metal nanoparticles were directly associated with the formation of 'senile plaques' – lesions on the brain and one of the neuropathological hallmarks of Alzheimer's disease and dementia. Despite such strong links, Ekström argues it is only recently that researchers have "opened their eyes to the olfactory sense" and its role in disease. Loss of smell has bee n linked to increased likelihood of depression and anxiety in various studies, and is known to play a role in obesity, weight loss, malnutrition and cases of food poisoning. The reasons are perhaps obvious – our noses play a key role in our experience of the world around us, affect our ability to taste food and help us avoid meals that have gone off. A poor sense of smell may mean that sufferers are likely to seek out stronger tasting food, which is very often salty and fatty. By contrast, a total loss of smell can put people off food and lose enjoyment from it, ultimately becoming underweight – a particular problem amongst the elderly.  Ramanathan has seen many patients who "can't taste food, can't smell their wine, the things that gave them pleasure in life". He recalls one patient who was a professional sommelier, for whom developing anosmia was both personally and professionally devastating. Smell and taste are also linked to memory. "People don't remember what that pastry looked like that they ate in France, but they remember what the shop smelled like", says Ramanathan. Re-experiencing a particular smell can transport our memories straight back to that moment in pastry shop. This raises the question – albeit yet to be properly studied – whether the inverse could also true, and no longer being able to smell could impair our ability to create new memories in the same way. Anosmia could also be an indicator of other, wider health issues. Numerous studies, typically of smokers – for whom smell impairment persists even 15 years after quitting – have shown that olfactory dysfunction is significantly associated with increased mortality among older adults. One particular study even hypothesised that anosmia could be used as a predicator for greater likelihood to die – from any cause – amongst older adults over a five-year-period. In a study of 3,005 US adults aged 57 to 85, those with anosmia were found to be four times more likely to die than their peers five years later. The researchers concluded that deteriorating sense of smell could be a "bellwether" for the accumulation of toxins from the environment or slowed regeneration of cells. So, should we care that air pollution – to which we are all exposed – is impairing our sense of smell and causing anosmia? Clearly, the answer lies somewhere between "yes" and "hell yes". Ramanathan, for whom traffic pollution and waste incinerators top the local pollution concerns in Baltimore, says "air quality matters". "I think we need tight regulations and control," he says. Many people may not even realise the pollution they are exposed to, so they rely on politicians regulating it to protect the populations in the surrounding areas. "This is one of many [pollution-related] conditions," adds Ramanathan. "But this is kind of a special one, right? If you have COPD [chronic obstructive pulmonary disease] you could probably still enjoy your glass of wine. But not with this one." Ekström says tackling air pollution is not simple. World events can also cause unexpected shifts in behaviour – Ekström mentions anecdotally that winter wood burning has been on the rise in Stockholm as worried residents wean themselves off Russian gas. But even the every-day, low-level air pollution we are exposed to  “should be taken more seriously", she says. And what's more, “olfactory impairment should definitely be taken more seriously”, too. * Tim Smedley is author of Clearing The Air: the Beginning and the End of Air Pollution, published by Bloomsbury.

Want to live to be 100? Here’s what experts recommend.

Want to live to be 100? Here’s what experts recommend. The recent death of the world’s oldest person at age 118 highlights the growing number of centenarians around the world Teddy AmenabarJanuary 25, 2023 at 12:50 p.m. EST A woman turning 100 blows out her birthday candles. (iStock) Experts predict that the number of centenarians — people who live to be at least 100 years old — will continue to rise in the coming decades. While genetics play a large role in healthy aging, physical activity, social support and where you live also can influence your chances for living a very long life. Sister André, a French Catholic nun born Lucile Randon, who was the world’s oldest living person, recently died at the age of 118. Now the two oldest living people are believed to be María Branyas Morera, a 115-year-old Spanish woman born in the United States, and Fusa Tatsumi, who lives in Osaka, Japan, who is also 115 but 52 days younger than Morera, according to a database by the Gerontology Research Group. Based on a 2022 estimate by the United Nations, there are 593,000 centenarians around the world. It’s a fast-growing age group. The United Nations projects there will be 3.7 million centenarians alive by 2050. Did you win the genetic lottery? Experts who study the expanding human life span say the reason someone may live beyond 100 years starts with their DNA — the genes they’ve inherited from their parents. “You can’t make it out that far without having already won the genetic lottery at birth,” said S. Jay Olshansky, a professor of public health at the University of Illinois at Chicago. “So, rule number one is going to be genetics.” The longer your parents live, the more likely you’ll live a healthier, longer life, experts say. Luigi Ferrucci, the scientific director at the National Institute on Aging, said the children of centenarians typically live healthier, longer lives than their peers. “It’s probably not one single gene but a profile, a combination of genes,” Ferrucci said. Living to 100 complicates retirement Nir Barzilai, the director of the Institute for Aging Research at the Albert Einstein College of Medicine in the Bronx, has studied the lives of hundreds of centenarians, the people they’ve married and their kids. The children of centenarians are “about 10 years healthier” than their peers, Barzilai said. Barzilai is working with others to enroll 10,000 centenarians, their children and a control group from the general population to identify the different genes that contribute to a long life. People who have a certain mutation on their growth hormone, for example, are “very likely to live longer” because their cells spend more energy on maintaining existing cells, not growing new ones, Barzilai said. The plan is to use artificial intelligence to help find the genes and develop drugs from them, he said. “We really want to find all the longevity genes,” Barzilai said. Olshansky said he and his colleagues are preparing to launch a platform in February where people can upload data from a genetic testing service to identify whether they have genes “associated with exceptional longevity,” so they can plan financially for retirement. “I’m a carrier, for example, of two sets of genes that are associated with longevity,” Olshansky said. “For planning purposes, I probably need to delay retirement.” Environment and lifestyle count Experts disagree on how much genetics influence a person’s life span vs. their lifestyle. But most experts say that good genes will only get you so far. Jamie Justice, an assistant professor of gerontology at Wake Forest University, says some research has suggested that genetics account for around 25 percent of longevity. The other 75 percent relates to your environment — where you live, what you eat, how often you exercise and your support system through friends or family. For those of us who are not endowed with a set of promising genes, the goal isn’t to push the boundaries of human life expectancy, Justice said. Instead, researchers want to figure out how people can have full, healthy lives with the time they have. “The goal isn’t necessarily to live to 118 years. It’s to live well within those years,” Justice said. “What individual things do we do that we can really harness our health and live healthier within the years given?” And, Justice said, a good public health system “can’t be undersold.” If you have a better health-care system, you’re going to have a higher life expectancy, she said. The world’s oldest person record stood for decades. Then came a Russian conspiracy theory. And location matters, too The United States and Japan have the most confirmed centenarians and supercentenarians, people who live to be 110 years old or older; and, Japan has the most per capita, according to Robert Young, the director of supercentenarian research at the Gerontology Research Group. But, there are probably more centenarians and supercentenarians we don’t know about. More than 110 years ago, certain countries were better at creating and preserving birth certificates or hospital records, Young said. A country’s record-keeping a century ago is often the factor determining where confirmed supercentenarians are reported across the world, he said. “People need to remember that when we’re looking at human longevity today, we’re actually looking more at the state of the world 110-plus years ago,” Young said. Beyond record-keeping, where someone lives — a war zone, a place with access to quality health care, a country with a lot of pollution, a developed nation where people sit a lot — probably plays a significant role in longevity. Researchers have recently found “the stress of life directly affects some of the biological mechanisms of aging,” said Ferrucci, adding that our exposure to various types of pollution can harm our overall health, as well. He called the topic an “expanding area of research” that could revolutionize how we approach public health. “We are discovering that the secret of good health is not only in our behavior but it’s also in what our society does to enhance the health of our population,” Ferrucci said. And, from studying centenarians, Ferrucci said researchers have found that healthy older adults tend to be remain physically active, spend time outside and have strong connections with their friends and family. “Just walking outside,” makes an enormous difference, Ferrucci said. “If I had a jewel to give to people who want to live long and well, I would tell them to get up early in the morning and go out,” Ferrucci said. “That is really the best gift that you can give yourself if you want to achieve longevity.” Still, Ferrucci said centenarians and especially supercentenarians are often “unique.” Some people have this “biological resilience” to live a long life despite everything going against them. “There’s the curve of mortality that characterizes the general population and then there are these individuals that are unique singularities,” Ferrucci said. “We don’t know how and that is the great secret.” Experts say the usual advice of regular exercise and eating healthy food applies generally to all aging adults, but for a few centenarians, there are exceptions to the rule. Barzilai once visited a centenarian, and when she opened the door, she was smoking a cigarette. “I said, ‘Helen, nobody told you to stop smoking?’ ” Barzilai said. “And she said, ‘You know, the four doctors who told me to stop smoking? They all died.”