Johns Hopkins Medicine researchers have studied how long-term exposure to air pollution causes loss of smell, or anosmia, to better understand how it can rob someone of the ability to smell and taste.
Anosmia can severely impact a person’s quality of life, making it extremely difficult to taste foods, detect airborne hazards in the environment, and other functions. People with anosmia may experience weight concerns, decreased social interaction, depression and general anxiety. Loss of smell has been linked in some cases to death in older adults.
“We included participants from a variety of areas in our study; however, most lived in urban areas where pollution levels are highest,” says lead author Murugappan “Murray” Ramanathan, MD, rhinologist and associate professor of otolaryngology–head and neck surgery at the Johns Hopkins University School of Medicine. “We wanted to assess how their exposure to PM2.5 air pollution—inhalable, particulate matter less than 2.5 micrometers in size or about 30 times smaller than the diameter of a human hair—might cause them to lose their sense of smell.”
According to the US Environmental Protection Agency (EPA), PM2.5 (the PM stands for ‘particulate matter’) is the term for a mixture of solid particles and liquid droplets found in the air, and are smaller even than pollen grains. PM2.5 can be made of many materials depending on the location, such as dust, dirt, soot, smoke, organic compounds and metals. These particulated have been linked to cardiovascular disease, lung cancer, cognitive decline, chronic obstructive pulmonary disease, asthma and premature death. Previous studies have suggested PM2.5 is a likely culprit in loss of smell—a connection that Prof Ramanathan and his team decided to explore in greater detail.
In their study, the researchers examined data for 2690 people, aged 18 years and older, who were evaluated by otolaryngologists between January 2013 and December 2016. Of these, 538 were diagnosed with anosmia, with an average age of 54, the majority being men (63%).
The EPA’s Air Quality System provided air pollution data for the study. The researchers entered the data into a detailed computer simulation to estimate the PM2.5 pollution levels within the participants’ residential ZIP codes. The model was created by Zhenyu Zhang, a Johns Hopkins Medicine otolaryngology postdoctoral fellow.
The researchers found that long-term airborne exposure to PM2.5 nearly doubles (a 1.6- to 1.7-fold increase) the risk of losing one’s ability to smell. They believe this may occur due to the location of the olfactory nerve—which contains the sensory nerve fibres associated with the sense of smell—being directly in the path of inhaled PM2.5 materials.
“Based on this result, we feel that long-term exposure to high levels of PM2.5 represents a common risk factor for the loss of sense of smell, especially in vulnerable populations such as older people—but also one that is potentially modifiable if sources of PM2.5 components can be better controlled,” says Ramanathan.
The researchers next steps are to study anosmia patients’ socioeconomic factors to find out if they affect the chances of exposure to PM2.5 air pollution. They also hope to evaluate other air pollution components that may contribute to loss of smell, such as ozone.
Source: Medical Xpress
Journal information: Zhenyu Zhang et al, Exposure to Particulate Matter Air Pollution and Anosmia, JAMA Network Open (2021). DOI: 10.1001/jamanetworkopen.2021.11606
