Breathing in tiny particles of air pollution over a long period of time may put your sense of smell at risk, a new study suggests.
Researchers found the risk for loss of smell - a condition called anosmia - was nearly doubled among people with lengthy exposure to this type of air pollution, known as particulate matter.
"It's curious that the entire group who had lost their sense of smell had a significantly higher exposure to 'particulates,' compared to the group that didn't develop the disease," said lead researcher Dr. Murugappan Ramanathan. He is an associate professor of otolaryngology at Johns Hopkins University School of Medicine, in Baltimore.
These tiny particles are less than 2.5 micrometers in size, or about 30 times smaller than the diameter of a human hair. Known as PM2.5, they're tied to a variety of health problems, such as heart disease, lung cancer and asthma.
PM2.5 is produced by diesel cars and trucks. It can be made up of many materials, including dust, dirt, soot, smoke, organic compounds and metals.
Ramanathan cautioned, however, that this study can't prove exposure to PM2.5 causes anosmia, only that there appears to be a connection.
It's unclear in this study if loss of smell was caused by air pollution damaging nerves that control the sense of smell or by inflammation in the nasal membrane. It's also not clear if the loss of smell is permanent.
"Typically, when sense of smell comes back, it's usually after a viral infection or when inflammation goes away," Ramanathan said.
In the case of COVID-19, a common symptom is anosmia. Some people who get the infection lose their sense of smell and regain it, but for some, it doesn't come back, even after a year, he noted.
All of the patients with anosmia in this new study had the condition for a long time, the study authors said.
For the paper, Ramanathan's team looked at nearly 2,700 adults, including more than 500 with anosmia. Using the U.S. Environmental Protection Agency's Air Quality System, the researchers created a model to estimate the PM2.5 pollution in the participants' ZIP codes.
The investigators found that long-term airborne exposure to PM2.5 increased the risk of losing your sense of smell by about 1.7-fold.
Anosmia can affect quality of life, making it hard to taste foods and detect harmful odors. People with the condition are at risk for weight loss and for depression and anxiety, the researchers said in background notes.
Ramanathan said there isn't much any one individual can do to reduce exposure to air pollution.
"There needs to be better regulation of air quality," he said.
Kara Hoover, an associate professor of biological anthropology at the University of Alaska in Fairbanks, specializes in the sense of smell. Like many other health problems, she said, loss of smell is worse among poor and minority populations who tend to live in areas with higher levels of air pollution.
There is little someone in those circumstances can do to lower their risk, she added.
"The higher your socioeconomic status, the more access you have to buffers that affect pollution, like riding in your air-conditioned car rather than taking public transit or living in areas outside the city or in areas that have more parks and green spaces, which helps clear some of the pollution," Hoover said.
Hoover and Ramanathan agreed that reducing air pollution can only be accomplished by society as a whole.
"I don't think it's down to the individual," Hoover said. "I think it needs to be a top-down change."
The report was published online May 27 in JAMA Network Open.
For more on the loss of the sense of smell, head to Yale University Medical School.
SOURCES: Murugappan Ramanathan, MD, associate professor, otolaryngology, Johns Hopkins University School of Medicine, Baltimore; Kara Hoover, PhD, associate professor, biological anthropologist, University of Alaska, Fairbanks; JAMA Network Open, May 27, 2021, online