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Smoking does increase the risk of getting coronavirus, according to a major British study that disputes growing evidence that the habit is protective.
A team at Imperial College London, King’s College London and Zoe – the developer of a symptom-tracking app – looked at 2.4million Britons, of which 11 per cent reported smoking.
All participants were users of the COVID Symptom Study app, which asks people to regularly report their health and if they have symptoms of the coronavirus, helping to build a clearer picture of the UK’s outbreak.
Current smokers were 14 per cent more likely to develop tell-tale symptoms, such as a persistent cough and high temperature, suggesting a diagnosis of COVID-19.
They were also 50 per cent more likely to suffer other symptoms, such as diarrhoea, loss of appetite and delirium.
In addition, current smokers who tested positive were more than twice as likely to need to attend hospital due to COVID-19.
Smokers are known to be at higher risk of catching other viruses because they touch their mouth more and the potent chemicals damage airways.
Mounting evidence has suggested smokers are at less risk of COVID-19 but are more likely to get severely sick if they catch it.
Researchers across the world have discovered very low numbers of smokers among hospitalised COVID-19 patients, suggesting they are protected.
But the data has been full of holes because doctors are not always able to find out if someone severely sick is a smoker.
It’s left scientists split on the topic, with some so convinced smoking is protective against COVID-19 they are planning to trial nicotine patches as a preventative tool.
A review of 28 studies by University College London in April found a ‘lower than expected’ rate of smokers among COVID-19 patients.
One of the studies showed that in the UK the proportion of smokers among COVID-19 patients was just five per cent, a third of the national rate of 14.4 per cent.
Another found in France the rate was four times lower. In China, a study noted 3.8 per cent of patients were smokers – despite more than half of the population regularly smoking cigarettes.
But researchers have often noted that low prevalence of smokers may just be because doctors are just too busy to be accurately noting down everyone’s smoking habits, or patients are too unwell to speak.
Considering elderly people are more likely to be hospitalised with COVID-19, low smoking rates may be explained by differences in smoking rates in different age groups, with middle-aged people more likely to have the habit.
There is often data missing in these studies too, which could skew results.
The team at Imperial College London, led by Dr Nicholas Hopkinson, have taken a different approach to the majority of studies so far which used hospital data.
They used information from the COVID-19 Symptom app, which was developed by King’s College London to help track the crisis.
More than 3.6million people in the UK have downloaded the app since March.
On first use, the app records self-reported location, age, and core health risk factors, including height, weight, smoking and common disease.
Users are told to regularly report their health and if they develop symptoms of the coronavirus – up to 14 – and the results of a test if they get one.
For this study, the researchers took data from 2.4million who had entered data via the app between 24th March and 23rd April 2020.
Some 11 per cent of the group were smokers. The researchers said this may be lower than the national average (14 per cent) because wealthier people are less likely to smoker while also be more likely to have a smartphone.
The main finding was that current smoking was linked with a ‘substantially increased risk of developing symptoms suggestive of COVID-19’.
Among ‘standard users’ – those who never actually had a test – current smokers were 14 per cent more likely to develop the classic triad of symptoms of COVID-19 than non-smokers.
These were a fever, persistent cough and shortness of breath.
They were also 29 per cent more likely to have more than five symptoms, and 50 per cent more likely to have more than 10 symptoms.
These included abdominal pain, chest pain, delirium, diarrhoea, fatigue, headache, hoarse voice, loss of smell, skipped meals, sore throat and unusual muscle pains.
The researchers said this indicated their disease was more severe because those that reported going to hospital tended to have more symptoms.
The study then looked at people who had actually received a test result for COVID-19, where results differed slightly.
They first pointed out that smoking prevalence was two per cent lower in the group that got tested compared to those who did not.
This, they said, was because healthcare workers are more likely to get a test, but also less likely to be smokers.
Due to testing limitations in the UK, only healthcare workers or people in hospital were able to get a test at that time.
There were less smokers in the group who tested positive than negative (7.4 per cent vs 9.3 per cent), suggesting smoking is protective.
However, the researchers said smokers were more worse affected.
People with a positive result were 42 per cent more likely to have more than 10 symptoms, suggesting they suffered more than their non-smoker counterparts.
In addition, current smokers who tested positive were more than twice as likely to need to attend hospital due to COVID-19.
This risk only dropped marginally when pre-existing health conditions were taken into account.
The findings are in stark contrast to smaller and less accurate papers so far, citing a lower risk of hospitalisation in smokers.
The authors concluded in their pre-print paper, which has not been peer reviewed by other scientists: ‘Our results provide compelling evidence for an association between current smoking and individual risk from COVID-19, including symptom burden and risk of attending hospital.’
In light of emerging evidence that smokers make up low numbers of hospital patients, scientists have discussed how nicotine affects the expression of ACE-2 receptors.
ACE-2 are proteins in the body the virus binds to in order to infect cells.
If nicotine does lowers ACE-2 expression, it makes it harder for viral particles to gain entry into cells and therefore cause an infection.
But if it enhances ACE-2 receptors, in theory, this puts smokers at higher risks of catching the coronavirus.
To put this to bed, the Imperial team measured ACE2 expression in adipose tissue, which is made of fat cells.
The samples came from 541 women including 54 smokers, 196 past smokers and 291 non-smokers.
Smokers were found to have reduced ACE2 expression in adipose tissue compared to non-smokers.
This would suggest smokers are less likely to catch the coronavirus. However, the research in this area is so vague it is difficult to say whether this is the case.
Even Dr Hopkinson and colleagues wrote the matter was ‘complicated’.
What is more clear, is that lower numbers of ACE-2 receptors appear to exacerbate the disease because they are protective against lung injury.
The virus itself is known to cause lung damage by depleting the numbers of ACE-2 receptors. Therefore, if nicotine reduces ACE-2 receptors, this would make matters even worse.
But on the other hand, if nicotine boosts ACE-2 receptors, as suggested by other research, withdrawal from it during a hospital stay would also potentially lead to worse outcomes.
Studies have shown nicotine may prevent a severe over-reaction of the immune system called a cytokine storm – a phenomenon found to be killing many COVID-19 patients.
Welsh NHS doctors who want to do COVID-19 trials with medicinal nicotine patches based on the theory the addictive chemical is protective in some way.
Doctors at The Royal Glamorgan Hospital are currently waiting for funding and ethical approval to move forward with a trial of some kind.
Researchers in France are also planning a trial after finding low levels of smokers in a hospital in Paris.
The move would be controversial, considering studies such as that by Imperial warn smoking is a risk factor for COVID-19.
DailyMail