Approximately every second person who falls ill with covid-19 has a changed sense of smell and taste. Most people regain both smell and taste within a week, but about one in five still have problems a year after covid’s disease.
Now researchers have found two genes that increase the risk of suffering from impaired sense of smell by 11 percent.
– It is not a huge increase in risk, but interesting because the discovery of the genes in the long run can provide new drugs and preventive treatments, says Johan Lundström, who researches the sense of smell and is an associate professor of clinical neuroscience at Karolinska Institutet.
The study is published in the scientific journal Nature Genetics. It is based on data from almost 70,000 Americans and Britons included in the genetic testing company 23andMe’s Covid-19 study. The genes are called UGT2A1 and UGT2A2, and are more commonly found in people of European descent. The genes affect the function of the olfactory receptor support cells located in the olfactory mucosa of the nose.
It is still unclear how covid disease affects the sense of smell. Johan Lundström explains that there are two main theories: The first is about the part of the olfactory mucosa that is at the top of the nasal cavity. It is called the olfactory epithelium and has cells that sense odors. Next to the olfactory cells are support cells, which have a special receptor (ACE2) that the virus uses to enter cells. The researchers believe that the coronavirus kills the support cells, and then the olfactory cells also die. Here, the newly discovered genes probably play a certain role.
– Within about four weeks, new odor cells have formed, says Johan Lundström.
The second theory is more controversial. It is about the virus also affecting the part of the brain called the olfactory bulb. It sits just behind the eyebrows, and receives information from the olfactory cells via the olfactory nerve. Researchers have found signs of inflammation in the olfactory bulb in people who have died in covid-19.
This is why many people lose the smell when covid
The coronavirus probably knocks out support cells in the olfactory mucosa of the nose, which leads to the odor cells dying.
Graphics: DN Source: Johan Lundström, KI.
– We have done studies with a magnetic camera that indicate that the odor bulb is smaller in those who have covid disease, says Johan Lundström.
He believes that the explanation for lost smell and taste (called anosmia) is probably a combination of the two theories.
To date, almost every second adult Swede has had covid-19. According to Johan Lundström’s estimate, this means that hundreds of thousands of Swedes have been affected by the sense of smell for a shorter or longer period of time.
– It can be a health problem in the long run. Initially, many people lose their appetite, lose weight and may become depressed. Then most people start compensating for the loss of taste with extra sweet, salt and fat and gain weight.
Johan Lundström sees no signs of fewer being affected by the new omikron virus variant.
– With omikron, many people think that they only get cold symptoms, and do not notice that they have a changed sense of smell.
Most people regain their taste and ability to smell. But when the sense of smell returns, food and drink can smell and taste different, something called parosmia. After a common cold, some parosmy get a shorter time, and only 5 percent get long-term problems.
– The unique thing about covid-19 is that 30-40 percent get problems that linger for a long time, says Johan Lundström.
Still there are no cures. The only treatment that has a proven effect is odor training, which means that you smell different scents twice a day for at least two months.
To avoid long-term problems, Johan Lundström believes that it is important to start odor training as early as possible. Those who smell smell have a higher chance of improving their sense of smell than those who do not.