MORE evidence smokers are at less risk of Covid-19: 23% less likely to catch the virus

Smokers are less likely to be diagnosed with Covid-19 compared to those who have never touched a cigarette, another study has claimed. 

An array of research carried out since the pandemic began has shown smokers are at lower risk of getting the coronavirus.  

Now researchers in Mexico have added more weight to the evidence, which experts have called bizarre and said warrants further investigation.

Scientists analysed data from almost 90,000 patients and results showed smokers were 23 per cent less likely than non-smokers to get diagnosed with Covid-19. 

And the team also found smokers who did get infected were no more likely to need intensive care, be hooked up to a ventilator or die. 

The findings support the theory that smokers are somehow protected from Covid-19, with data from Britain, the US, China and Italy all suggesting the same. 

Scientists are starting to believe nicotine may be able to block the coronavirus from entering cells, preventing the infection in the first place. 

Others say nicotine may control the immune system, stopping it from dangerously over-reacting to infection – a phenomenon found to be killing many Covid-19 patients. 

Doctors are keen to trial nicotine patches in the fight against Covid-9. But they have warned against encouraging smoking tobacco because of its known dangers. 

The study was a joint investigation by scientists in Mexico, Greece and the US, led by Dr Theodoros Giannouchos of the University of Utah.

The team said to the best of their knowledge, this is the largest study of patients with a confirmed Covid-19 diagnosis.

It included 236,439 people who had been to a medical centre with a suspected viral respiratory illness – 89,756 tested positive for Covid-19 and 146,683 tested negative.

Any underlying health conditions, such as diabetes, were noted down. The team also identified whether or not the patient was a smoker.

People were classified as either a smoker or non-smoker – ‘former smoker’ was not an option but the scientists did not explain why.

Most patients were 18 to 44 years old and Mexican. Around 40 per cent of all patients had one or more co-morbidities. 

Some 8.3 per cent who were diagnosed were current smokers. In contrast, around 14 per cent of adults in Mexico are estimated to smoke.

Researchers identified the main risk factors for Covid-19 by comparing the data of those with a positive or negative test. 

Smokers were 23 per cent less likely to be diagnosed with Covid-19 compared to non-smokers, the findings claim.

Of those who were diagnosed, smokers were six per cent less likely to be admitted for hospital care compared to non-smokers. 

No major differences were observed between the current smokers and non-smokers when looking at adverse outcomes, including ventilation and death.

The study found Covid-19 patients were most likely to be older, male, and have an underlying health condition. 

Patients with diabetes, obesity, high blood pressure and COPD were the most vulnerable patients both to infection and death.

One in five patients with Covid-19 had at least one comorbidity – and they were three times more likely to end up hospitalised or dead. 

The researchers, whose findings have yet to be peer-reviewed in a scientific journal, said the results were not ‘unexpected’.

They added that ‘multiple comorbidities contribute to disease complexity and such patients are more susceptible and vulnerable to adverse events’.

‘Notably, smoking was not associated with a higher risk for adverse outcomes and hospitalization,’ the team wrote in their paper published on medRxiv. 

‘Smokers were also less likely to be diagnosed with Covid-19.’ The experts added that the findings were ‘in agreement’ with a study from Israel.

The Israeli study referenced, published last week, pooled data from more than three million people, including 115,000 swabbed for the virus. 

Dr Ariel Israel and his colleagues uncovered a ‘genuine’ protective effect of smoking. They also published their findings on MedRxiv.

Ten per cent of patients who tested positive for Covid-19 were smokers, compared to 19 per cent in the general population. 

The findings only add weight to a number of small studies from when the pandemic began, which say smokers are protected from the coronavirus.

The findings present a hypothesis that nicotine – the highly addictive compounds in tobacco – may exert protective effects.  

It is broadly understood that SARS-CoV-2 – the virus that causes the disease – enters the body by binding to receptors in the body called ACE-2, which are found along the respiratory tract.

Some research suggests nicotine reduces the expression of ACE-2, which would suggest smokers have less entry points for the virus to begin with. 

But other scientists, including Dr Giannouchos, say nicotine is thought to boost the expression of ACE-2 receptors which coat the cells. 

While this would imply smokers are at more risk of catching Covid-19, there is evidence that they are less likely to be hit by a severe bout of the disease.

‘ACE-2 deficiency’ may be detrimental to Covid-19 patients, Dr Giannouchos wrote, noting that risk factors for severe illness from Covid-19, such as age, male gender, and some diseases, are linked with lower levels of ACE-2.  

Nicotine has been shown to prevent lung damage in animals with acute respiratory syndrome, a life-threatening condition the coronavirus can lead to. 

It’s been suggested that if smokers do see their disease progress while in hospital, it is due to withdrawal from nicotine, exacerbating lung damage.  

Another theory is that the virus first enters via the nicotinic acetylcholine receptor (nAChR), which is present around the nose and mouth.

This would explain why the virus causes a loss of taste and smell and in some cases, headaches, dizziness and intense fatigue.

Researchers from Paris wrote in a paper published on Qeios that nicotine would compete with the virus to bind to nAChR, and therefore may prevent the virus from latching on.

Severe Covid-19 has been shown to cause a ‘cytokine storm’ – a hyper activation of the immune response which can be fatal to healthy organs.

Research also suggests nicotine may prevent this severe over-reaction of the immune system by reducing the levels of cytokines circulating in the body. 

Dr Giannouchos and colleagues concluded in their paper: ‘It is still not clear whether nicotine exerts any positive effect or not. 

‘However, there is no doubt that smoking cannot be used as a protective measure and smoking cessation should be encouraged during the Covid-19 pandemic. 

‘The potential value of nicotine or other nicotinic agonists in Covid-19 is expected to be determined through clinical trials.’

Indeed, researchers are pushing for clinical trials of nicotine patches, with the hope they can determine exactly what is going on. 

Jonathan Davies, a consultant trauma surgeon at The Royal Glamorgan Hospital, Wales, told MailOnline the hospital is looking at a number of possible points at which nicotine might be a valid intervention. 

He said: ‘In a nutshell, the question is: Are people who smoke see to be less likely to catch it? Does nicotine given to people who don’t smoker offer some sort of protection?

‘I would like to get a cohort of people in the general population and give half a nicotine patch for six week and the other half a placebo path and then see if there is a difference in antibodies [which indicate coronavirus infection].’

It follows the lead of researchers in France, who are also planning a trial after finding low levels of smokers in a hospital in Paris.

Only one notable study so far has thrown out the claims smoking is protective against Covid-19.  

A team at Imperial College London looked at 2.4million users of the COVID Symptom Study app, developed by King’s College London and Zoe. Some 11 per cent of the group were smokers. 

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. 

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, such as diarrhoea, loss of appetite and delirium. 

The researchers said this indicated their disease was more severe because those that reported going to hospital tended to have more symptoms.   

The World Health Organization (WHO) said on May 26 there is a lack of knowledge about whether smoking alters the risk of catching the coronavirus or being hospitalised.

There are currently no peer-reviewed papers on the matter published in medical journals, meaning none have been looked over and critiqued by other scientists.

The data up until this point has been full of holes – which could skew findings – because doctors are not always able to find out if someone severely sick is a smoker, either because they are too busy or the patient is so unwell they cannot speak. 

Low smoking rates may be explained by differences in smoking rates between age groups, with middle-aged people more likely to have the habit, but elderly people more likely to be hospitalised with Covid-19.  

When it comes to disease severity and death, the WHO reports that available evidence so far suggests that smoking increases the risk, having looked over 35 published studies.

A review of five early studies on the topic early in the pandemic made the exact same conclusions – that smokers may avoid serious infection, but their outlook is worse if they do.

The team at Harvard University in Boston and the University of Crete in Greece  reviewed five Chinese studies in March and said so far say the proof smoking raises the risk of coronavirus is limited, after finding as little as 1.4 per cent of hospitalised patients were smokers. 

The group of experts even admitted warnings made by health chiefs were based mainly on assumptions, given the known infection risks of smoking. 

A recent Italian study found half of infected smokers died – compared to 35 per cent of the rest of the patients.

Fewer than five per cent of 441 Covid-19 patients who needed to be admitted to hospital were smokers – a ‘very low’ number, given that a quarter of the general population are known to be hooked on cigarettes. 

But once smokers are in hospital, they may be more likely to see their disease rapidly progress and lead to death. 

Information about smoking was taken from medical records, and efforts were made to directly contact the patients or their relatives for confirmation.

A leading infectious disease expert at University College London, Professor Francois Balloux, has also previously said there is ‘bizarrely strong’ evidence smoking may be protective.

And Linda Bauld, a professor of public health at the University of Edinburgh, said ‘there’s something weird going on with smoking and coronavirus’ on Good Morning Britain.