Thanks for taking the time to speak to us about intranasal Vitamin A treatment for patients with post-infectious smell loss, Katherine.
Q. Before we begin, could you tell us a bit about yourself?
A. I’m an Ear Nose and Throat surgeon (Dr in the US, Miss in the UK!) with a background in Neuroscience, and am currently a Research Fellow at the Technical University in Dresden, as well as the Centre for the Study of the Senses and University College London Hospitals. My particular interest is cross-discipline and translational research - turning basic science research into treatments for patients.
Q. Could you explain to our readers a little bit about Vitamin A therapy for patients who have lost their sense of smell after a bad virus?
A. Our sense of smell relies on activation of nerve cells that sit in the mucous layer at the top of our nose. By sitting in the mucous layer in this way, these cells are exposed to everything we breathe in - not just odours, but also harmful particles, including viruses, dusts and toxins, which can damage the nerve. To get around this, and maintain our sense of smell, these cells have a unique ability to regenerate and replace themselves. In some people, probably because of an accumulation of damage throughout their life, this regenerative capacity can be overwhelmed after an infection (usually viral, but can also be due to other types of bug, for example bacteria - for this reason we should use the term post-infectious rather than post-viral).
Vitamin A is metabolised in our body into a substance called retinoic acid. This active form is involved in regulating the expression of genes within our cells and has been found in lab work to be important for nerve cell development. Because of this, it’s theorised that taking Vitamin A might help the olfactory nerve cells that have been damaged in post-infectious hyposmia/anosmia to start regenerating again. The first study looking at this was in the 1960s, and though positive results were seen, the study was poorly designed so it is difficult to trust the outcome. More recently, I worked with Prof Hummel to publish research showing that topical (nasal drops) Vitamin A used in addition to smell training improves olfactory function, when compared to smell training alone. This was particularly true in post-infectious patients. We need to look into this more, but it looks like it could be promising.
Finally, if you’re thinking about using Vitamin A - please only do so after your sense of smell has been properly assessed and under medical supervision. Beyond what we get naturally in a varied diet, Vitamin A should be treated as a medication as it can have potential side effects.
Q. Some of our readers are interested in taking Vitamin A in tablet form. Can you comment on this?
A. First and foremost, as I mentioned above, Vitamin A and its active metabolites are medications that should only be used under the supervision of a doctor. This is particularly the case with oral Vitamin A, which more readily enters the blood stream than its topical counterpart, and which therefore carries a higher risk of side effects. Putting all that aside, one of the most scientifically rigorous studies to assess the use of oral vitamin A was also done here in Dresden. Using a randomised and controlled study design, they found no significant improvement in smell function after a course of oral therapy. It’s possible that topical therapy works better (explaining the positive results Prof Hummel and I found, as described above) because it allows a higher localised dose to be delivered directly, and safely, to the olfactory nerve cells in the nose.
Q. What should recent post-viral smell loss patients know about looking after themselves, and what is the best way to approach the recovery period?
A. Post-infectious smell loss can be quite devastating at first, but it’s important to stay positive and proactive - many people do recover!
The first thing that is very important is that anyone who has lost their sense of smell is properly assessed by a doctor - ideally an ENT surgeon. Having established a diagnosis (including formal smell testing) - the next important thing is to start treatment as soon as possible - be that smell training alone, or smell training plus a more experimental treatment advised by your doctor. We know that smell training works better if it’s started sooner - especially within the first year following the infection. You may find other things helpful as well - for example allergen avoidance/antihistamines if you have hay fever type symptoms, and nasal salt water washes. Again your doctor can advise you about this. It’s also important to make sure you take steps to protect yourself from environmental hazards - make sure you have working smoke/gas detectors and always stick to use by dates on food! Finally, we know that in some people, smell loss can take quite a toll psychologically. This is partly because the parts of the brain that process emotion also process smell - so when the smell part isn’t working, it might put the whole system slightly off-kilter (if you want to know more about the link between smell, emotion and memory:https://aeon.co/essays/how-exactly-does-smell-unlock-buried-memories-from-the-past). So look out for yourself! And if you’re feeling like you might need some psychological support, please don’t be afraid to speak to your doctor.
Q. Do you have any other general words of advice for the people in this group? Bearing in mind that some are PV, but we also have TBI and CNRS patients here.
A. Again, I think first and foremost - make sure you have been properly assessed, including smell testing (with something like the Sniffin Sticks or UPSIT). We’re not very good at subjectively assessing our own sense of smell, so without formal smell testing, it is impossible to accurately diagnose smell loss or track any improvement or deterioration following treatment. Unfortunately, the medical profession as a whole (including ENT surgeons!) is still not great at thoroughly assessing smell loss. For this reason, we recently published guidelines on diagnosing and treating olfactory dysfunction. This is free to download (you can find it here. Look for the article in the lower left hand corner of the page) and might be worth showing to your doctor if they’re not familiar with the process!
To read the full article on Vitamin A, click here.