We’ve been losing our sense of smell since before covid

For many people, having Covid-19 has given them what it’s like to lose their sense of smell. Loss of the sense of smell, commonly known as anosmia, can significantly impair our overall well-being and quality of life.

The sense of smell is one of the richest and most comprehensive windows into the world around us. Its role is central to our food and social interactions. It even helps us detect potential dangers.

A sudden respiratory infection like COVID-19 can cause a temporary loss of this important sensation, but our sense of smell can gradually wane for years for another reason: air pollution.

Exposure to PM2.5—a collective noun for small particles of pollution suspended in the air, largely caused by fuel combustion in vehicles, power plants, and homes—has already been linked to “smell disorders,” but usually only in industrial or occupational settings. .

But new research is now beginning to reveal the true scale and potential harm caused by the pollution we breathe in everyday life – and its findings matter to all of us.

On the underside of our brain, just above the nasal cavities, is the olfactory bulb. This delicate group of tissue filaments with nerve endings is essential to the very diverse picture that the world sends us through our sense of smell.

The olfactory bulb is also our first line of defense against viruses and pollutants entering the brain. But with continued exposure, these defenses are slowly eroded or overrun.

Our data shows that there was an increase from 1.6 to 1.7 times [do risco] “Development of anosmia with persistent particulate matter pollution,” says Murugappan Ramanathan Jr., a rhinologist at Johns Hopkins School of Medicine in Baltimore, USA.

Ramanathan became one of the few experts in the field after he began to wonder if there was a connection between the large numbers of anemic patients he saw and the environmental conditions in which they lived.

He asked himself a simple question: Are there a disproportionate number of anemic patients living in areas with higher levels of PM2.5 pollution?

Until recently, little scientific research on the subject included a 2006 Mexican study, which used strong orange and coffee scents to show a trend: Mexico City residents (who have frequent problems with air pollution) have, on average, a weaker smell than people. living in rural areas of the country.

Ramanathan enlisted the help of colleagues such as environmental epidemiologist Zhenyu Zhang, who created a map of historical air pollution data in the Baltimore area. This support enabled a case-control study using data from 2,690 patients at Johns Hopkins Hospital over a four-year period. About 20% of them suffer from anosmia and most of them do not smoke – a habit known to impair the sense of smell.

Confirming the hypothesis, PM2.5 levels were found to be “significantly higher” in neighborhoods where patients with anosmia lived, compared to healthy participants.

Until adjusting the results for age, sex, race, body mass index, and alcohol or tobacco use, the conclusions were the same. According to the study, “Even small increases in exposure to PM2.5 in the environment can be associated with anosmia.”

These findings have been confirmed in other parts of the world, in studies published this year. A recent study in Brescia, northern Italy, found that the noses of teens and young adults became less sensitive to odors, and the more they were exposed to nitrogen dioxide — another pollutant produced by burning fossil fuels, particularly by engines. . of vehicles.

In Brazil, a year-long study in Sao Paulo also indicated that people who lived in areas with a higher concentration of particles had a reduced sense of smell.

Why?

How, exactly, does pollution damage our ability to smell?

According to Ramanathan, there are two possible answers. One of them is that some pollution particles pass through the olfactory bulb and go directly to the brain, causing inflammation.

“The olfactory nerves are in the brain, but they have tiny holes at the base of the skull where the little fibers go to the nose, like little pieces of angel hair spaghetti,” says Ramanathan. “They are exposed.”

In 2016, a team of British researchers found tiny metal particles in human brain tissue, which appear to have passed through the olfactory bulb.

The study was led by Professor of Environmental Sciences Barbara Maher from Lancaster University, UK. At the time, she said, the particles were “surprisingly similar” to air pollution found near busy highways. Other possible sources were home stoves and wood stoves.

Maher’s study suggests that these metal nanoparticles can become toxic when they reach the brain, contributing to oxidative brain damage that impairs neural pathways, but this is still a theory.

The other possible mechanism, according to Ramanathan, may not even require pollution particles to reach the brain. Hitting the olfactory bulb nearly every day, the particles cause inflammation, direct damage to nerves, and slowly erode them.

It’s a bit like coastal erosion, which happens when salt waves wash sand away from the shore. Just exchange the waves for polluted air and the coast for our nasal nerves.