Vitamin D and COVID-19
13/11/2020
Loss of Taste and Smell in COVID-19
Most of our patients who suffered from COVID-19 had a short illness. For many, it has been anything but. Within this group of “long COVID” sufferers are those who had changes to taste and smell.
Changes to, or loss of, taste and smell were not initially recognised as linked to COVID-19. It took until May for the UK Chief Medical officer to include these as symptoms. They are now regarded as cardinal symptoms of infection with SARS-CoV-2.
How Common is Smell and Taste Alteration in COVID-19?
In Western Countries, taste perception is altered in 50% of COVI-19 sufferers. Altered smell is reported in 58% of COVID-19 patients in Western Countries. Interestingly, in East Asia, far fewer COVID-19 sufferers complain of changes to taste or smell. There are two possible explanations for this. The first is that the different strains of COVID-19 are predominant in each part of the world. These different strains may have different effects on our ability to taste and smell. The second explanation relates to the different genetics of people in the West compared to people in East Asia. Specifically, how our genes affect the ACE2 receptor. The is the receptor the SARS-CoV2 virus binds to. Our genetics determine the expression of the ACE2 receptor. That is, how easily the virus binds to the receptor and how many of the receptors are there.
What is the Mechanism of Taste and Smell Disturbance in COVID-19?
Most patients with COVID-19 do not have nasal congestion. This makes obstruction of the nose an unlikely cause of loss of taste and smell in COVID-19. It is thought that the most likely mechanism of altered smell in COVID-19 is through damage to sustentacular cells. These are support cells in the lining of the nose. They have a role in transforming and moderating smells. These cells usually regenerate quickly. Hence, the sense of smell usually returns rapidly in COVID-19. Nerve cells in the nose take longer to regenerate. Hence, it is possible that in people with prolonged loss of smell, there has been damage to nerve cells in the nose.
It is damage to olfactory receptor neurones, the nerves in the nose that is thought to be behind the phenomenon of parosmia. This is a distortion of the sense of smell. So wine can taste like gasoline and meat can taste rotten. Related to this is phantosmia. This is where phantom smells appear even if they are not there.
What can help?
The first thing to do is to consult your doctor to ensure that there is no other treatable or worrying cause of your loss of taste or smell. Most people will benefit from “Olfactory training.” This process uses strong smells and essential oils to stimulate the olfactory system. For people with nasal congestion, a steroid nasal spray can be of use. For those without nasal congestion, steroid drops are likely to be more helpful. A few people may find a short course of oral steroids helpful if they are safe to prescribe for that person. For those people who have very persistent symptoms, it is important to see an ENT surgeon for further investigations.