A new study suggests that a genetic risk factor may be linked to the loss of smell and taste from a COVID-19 infection.
The study was published Monday in the journal Nature Genetics.
Researchers at 23andme said they conducted a survey involving nearly 70,000 individuals who tested positive for COVID-19. Of those respondents, 68% reported having a loss of smell and taste. The study also noted that women were 11% more likely than men to report not having taste or smell after a COVID-19 infection. Seventy-three percent of people who suffered the loss were between 26 and 35 years old.
Researchers then conducted a genome study of those who reported the symptom and those who reported they didn’t have the symptom. Researchers found a location near two genes— UGT2A1 and UGT2A2— associated with the loss of taste and smell from a COVID-19 infection.
The authors said they aren’t sure how genes may be involved but noted that the coronavirus seems to impair cells that involve smell and taste. They also noted that their study does have limitations including the fact that they didn’t replicate the data and had to rely on self-reporting data.
The U.S. Centers for Disease Control and Prevention has said a loss of taste and smell is a common symptom of COVID-19.
For most people, the olfactory problems are temporary, often improving on their own in weeks. But a small minority are complaining of persistent dysfunction long after other COVID-19 symptoms have disappeared. Some have reported continued total or partial loss of smell six months after infection. The longest, some doctors say, are now approaching a full year.
Researchers working on the vexing disability say they are optimistic that most will eventually recover but fear some will not. Some doctors are concerned that growing numbers of smell-deprived patients, many of them young, could be more prone to depression and other difficulties and weigh on strained health systems.
Losing the sense of smell can be more than a mere inconvenience. Smoke from a spreading fire, a gas leak, or the stink of rotten food can all pass dangerously unnoticed. Fumes from a used diaper, dog’s dirt on a shoe or sweaty armpits can be embarrassingly ignored.
How can a virus cause smell and taste loss?
Other researchers believe one possibility is that people with upper respiratory infections often have congestion, drainage and other nasal symptoms that can block an odor’s ability to reach the smell nerve — which sits at the top of the nasal cavity, according to Vanderbilt University Medical Center.
But the primary cause, particularly for those with extended or permanent smell loss, could be due to the virus prompting an inflammatory reaction inside the nose that can lead to a loss of the olfactory, or smell, neurons.
"In some cases, this is permanent, but in other cases, the neurons can regenerate. That’s likely what determines which patients recover," the medical center states online.
Possible predictors of loss of smell and taste with COVID-19
Dr. Rakesh Chandra, a researcher at the Smell and Taste Center at Vanderbilt University Medical Center, said that generally, a person’s sense of smell can diminish with age, and women usually have a more astute sense of smell compared to men. But COVID-19 related smell loss is "disproportionally represented by younger females."
"That’s a little paradoxical compared to who generally gets smell and taste disorders, broadly speaking," he said.
Researchers don’t know why this would be the case. Chandra said it could be because their smell was better to begin with so the loss of it is more apparent — or perhaps another reason.
He added that patients with a milder COVID-19 infection are also more likely to have smell and taste loss, "so the disease severity seems to correlate in the opposite direction with the incidence of smell loss."
Previous research has shown similar findings.
How to boost chances of smell returning
Overall, those under 40 are more likely to recover these senses compared to older adults, the team at Virginia Commonwealth University found.
But to enhance one’s chances of recovering their sense of smell, researchers recommend what’s called olfactory training, which involves repeatedly smelling essential oils such as lemon, rose, cloves and eucalyptus for at least 20 seconds each twice a day.
This type of training should continue for at least three months — or longer if possible.
"Smell them one by one in order in the morning, and do the same thing in the evening, and every five days change the order," Chandra recommends. "It helps with odor discrimination and identification over time."
Kelly Hayes and the Associated Press contributed to this story. This story was reported from Los Angeles.