TORONTO -- Can nicotine protect against the novel coronavirus? Are smokers really contracting COVID-19 less often than non-smokers?
If you鈥檝e seen these questions posed in dramatic headlines recently, you might be more than a little perplexed. After all, isn鈥檛 smoking a risk factor for COVID-19?
There have been numerous studies related to COVID-19 and smoking released over the past few weeks, and sifting through them all provides a confusing picture of just how a history of smoking affects a COVID-19 patient鈥檚 prognosis -- or their chances of catching the virus in the first place.
Many studies have shown that when smokers end up in hospital with COVID-19, they have a much higher chance of developing severe complications, or dying.
But at least three recent studies have found a lower percentage of smokers among COVID-19 patients than the percentage of smokers in the general population.
Several news reports have used studies like these to suggest that current smokers may actually be protected from contracting the virus. But is this supported by the science?
In a nutshell, no.
CTVNews.ca talked to Eleanor Murray, an assistant professor of epidemiology at Boston University, to find out when and how these studies are being misinterpreted by media and the general public -- and why it鈥檚 a concern.
LOW NUMBER OF SMOKERS AMONG COVID-19 PATIENTS?
Two recent studies causing a stir are a Paris study released in late April, and a study conducted in Italy that released a preliminary paper this week.
Both reported low levels of smokers among COVID-19 patients, and both posited this could point to smoking providing some sort of 鈥減rotection.鈥
Murray was skeptical of this claim.
Her main issue with the studies she had taken a look at was their limited scope.
鈥淚'm seeing them report just the prevalence of smoking in the COVID patients and the prevalence of smoking in the general population. But for most areas, COVID patients are much older than the general population,鈥 Murray said.
鈥淭he life expectancy among smokers is lower than among non-smokers. And so it's entirely possible that if you're looking at a sample that's mostly older individuals, you might just expect any sample like that to have fewer smokers than the overall general population.鈥
In , researchers looked at 441 patients confirmed to have COVID-19 between March 5 and March 31, in Parma, northern Italy.
According to the most recent data from the World Health Organization (WHO), over the age of 15 are smokers. But less than five per cent of the COVID-19 patients were active smokers, the study said.
The median age of the patients was 71 years old. And of the 21 Italian smokers in the study who caught the virus, 11 died -- a mortality rate significantly higher than for the non-smokers.
The study noted that researchers only looked at symptomatic COVID-19 patients who were receiving treatment, and theorized that 鈥渟moking could attenuate the normal defensive function of the immune system, which becomes tolerant of a continuous inflammatory insult, while the immune system of non-smokers may be more prone.鈥
However, Murray pointed out that a similar theory could be used to explain why the number of smokers among confirmed COVID-19 patients is low.
鈥淚f smokers already have decreased lung capacity, they may not notice the milder symptoms of COVID, for example, and they may not [be] getting tested as much,鈥 she said.
took a different tack. Comparing 343 inpatients (those being treated in hospital) and 139 outpatients (those being treated at home), they found that only roughly five per cent of each group were daily smokers.
According to WHO, of those aged 15 and older in France are current smokers, and around 22 per cent are daily smokers.
Roughly 60 per cent of the outpatients and inpatients in the study identified as former smokers, however, leading to another problem: When did they quit?
The duration of a person鈥檚 smoking habit is a big confounder in this, Murray said. How long did a former smoker engage in the habit before they quit? How long has a current smoker been smoking regularly?
鈥淚t could be, 鈥榃ell, I smoked when [in] my teens, then I quit and now I'm 80 years old and yes, I am a former smoker, but it doesn't really have anything to do with my life right now,鈥 versus, 鈥極h, well, I saw on the news there was a respiratory disease going around and so I decided to quit smoking,鈥欌 Murray said.
Health officials all over the world have been stressing that smokers should quit in order to minimize their risk of complications if they catch COVID-19.
In the case of the France study, it muddies the data when it鈥檚 unclear what percentage of that 60 per cent quit smoking recently.
The France study also specified that they gathered this data by asking patients about their smoking habits, which leaves the possibility that some patients weren鈥檛 completely honest.
They acknowledge in the discussion portion of their study that 鈥渂ecause this is a cross-sectional study, we cannot confirm the causality of this association,鈥 between smoking and a potential protective effect. They also acknowledged that the outpatients they studied were from a limited area around a Parisian hospital, and that healthcare workers were over-represented in the outpatient group.
Their hypothesis is that it鈥檚 not the act of smoking that could protect people, but nicotine itself, theorizing that it could adhere to the cell receptors that the novel coronavirus targets and block the virus.
However, there is no proof of this yet.
The researchers said in April they planned to test further by using nicotine patches on health-care workers in a Paris hospital to measure if the nicotine could protect them, but these additional tests do not appear to have been carried out yet.
鈥淥ur findings should be interpreted cautiously,鈥 the initial study said.
These two studies aren鈥檛 alone in their findings.
Several other studies assessing smoking and COVID-19 in China and in the U.S. have found lower percentages of smokers among COVID-19 patients than would be expected. But no study has yet revealed a definitive 鈥渨hy,鈥 and Murray pointed out that there are many confounding problems to address, such as the impact of socioeconomic standing on smoking statistics.
鈥淭aking the conclusion from [preliminary studies] that there's some protective effect of nicotine is probably wishful thinking, just because there's really no clear evidence here either way of whether smoking is at all protective [against] COVID,鈥 Murray said.
The very idea of smoking being protective against COVID-19 is apparently enticing enough that even when researchers aren鈥檛 looking specifically at only smokers, it catches on.
Last week, Murray noticed a specific U.K. study on COVID-19 risk-factors that was gaining traction on Twitter -- for all the wrong reasons.
CURRENT SMOKERS DYING OF COVID-19 LESS THAN NON-SMOKERS?
The massive study, , was a collaboration between the University of Oxford and the London School of Hygiene and Tropical Medicine. It used anonymized records of 17 million adults in the U.K.鈥檚 National Health Service in order to create a list of numerous risk-factors for COVID-19 deaths.
But in the sea of data, what caught the eye of the public were some strange numbers that seemed to imply current smokers were dying of COVID-19 less often than non-smokers.
鈥淭he media immediately picked it up and ran with the idea that smoking is protecting people from dying from COVID, [along with other] really strong causal claims, which were not at all the goal of the paper,鈥 Murray said.
鈥淭he reason it's getting play is I think it's sort of feeding into things that people kind of wanted to be true.鈥
Murray explained in a 鈥溾 -- a Twitter thread unravelling the miscommunication -- that the main issue was finding conclusions where the study only presented observed correlations.
鈥淭here are lots of different goals for research studies and you know, identifying is this a cause of that is not always the goal,鈥 she told CTVNews.ca.
She said this study was simply aiming to describe potential risk factors that researchers might want to look into in the future regarding COVID-19.
In the study, there was a section assessing those who had never smoked, ex-smokers, and current smokers.
When researchers adjusted for only age and sex, current smokers were found to be 25 per cent more likely to die of COVID-19 than non-smokers.
But when researchers adjusted for the other risk factors they were looking at -- including heart disease history, weight, lung disease history, etc. -- current smokers were actually 14 per cent less likely to die of COVID-19 than non-smokers.
鈥淚f you compare smokers and non-smokers who have exactly the same age, level of heart disease, level of cancer history, et cetera, then the smokers seem to be doing better,鈥 Murray said.
This was 鈥渙ne of the big issues,鈥 with the study, she said, particularly when it came to the smoking data.
鈥淎n important thing to consider is that if you have heart disease and a history of cancer and you're a smoker, it's probably your smoking that has led to a lot of those health problems. But if you're a non-smoker and you're getting the same level of cancer history, heart disease, history, et cetera, as a smoker, it's 鈥 quite possible you have a lot of much worse things going on in your life. And so your general health might actually just be less good.鈥
In other words, smoking is too entangled in some of the other risk factors to adjust for them in this way. We can鈥檛 trust the 鈥14 per cent less鈥 figure because of the wider context.
鈥淎djusting for heart disease will make current smoking look related to COVID hospital death *even if it鈥檚 not*!鈥 Murray wrote in her original tweet thread.
She emphasized that the U.K. study itself was an 鈥渋mpressive effort,鈥 and that the 鈥済roup should definitely be commended鈥 for their work to compile all of this data.
WHAT HAPPENS WHEN SCIENTIFIC DATA IS TAKEN OUT OF CONTEXT?
鈥淭here's this issue of the media kind of running with [a study鈥檚] findings and over-interpreting them,鈥 Murray said.
She added that when she tweeted out her explanation of the U.K. study, some researchers who had worked on it thanked her for clarifying that they weren鈥檛 aiming to imply causation in the smoking data.
It can be dangerous for media and those with large audiences to boost medical theories that haven鈥檛 been proven, she said.
鈥淲e saw it even a few weeks ago when [U.S.] President Trump was sort of opining on possible medical uses of bleach,鈥 she said. 鈥淲e saw several cities 鈥 in the U.S. reporting [an] uptick in poison control calls after that of people who had ingested bleach.鈥
鈥淭here's definitely a risk that some people will make decisions which could be harmful for them based on these kinds of information.鈥
The World Health Organization on smoking and COVID-19, calling for researchers and media outlets to 鈥渂e cautious about amplifying unproven claims that tobacco or nicotine could reduce the risk of COVID-19.
鈥淭here is currently insufficient information to confirm any link between tobacco or nicotine in the prevention or treatment of COVID-19,鈥 the statement reads.
鈥淐ertainly we would not recommend someone to take up smoking based on [these new studies],鈥 Murray said. 鈥淎nd we would still be recommending that people quit smoking because smoking has a lot of negative [health effects].鈥
鈥淭hese misinterpretations can be dangerous for the individual and it can be dangerous for other people. It can be dangerous for society as a whole.鈥
So how can the general public know while reading a study, or a news article about a study, whether it contains advice for their daily life?
鈥淭he main thing is to sort of ask yourself, 鈥業f I was going to make a decision based on this [study], what type of action would I take?鈥 And then ask yourself whether anyone in the study took that action,鈥 Murray said. 鈥淚f the study can't tell you about what happened when people made that decision, you shouldn't rely on it to make a decision on your own.鈥
Edited by CTVNews.ca producer Michael Stittle
