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As the #COVID19 pandemic progresses, exactly why men get infected more frequently, and with greater severity, than women is unknown.

This #tweetorial examines a theory (emphasis on theory) that might explain some of this difference.

#medthread #medtwitter
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First, let's look at the gender distribution data for covid19.

It was noted early in the outbreak in China that more men than women were getting infected.

In this sample 58% of infections occurred in men (and they died at a slightly higher rate).

ncbi.nlm.nih.gov/pubmed/32109013
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A similar gender difference has emerged in Italy.

So far 59% of Italian cases have been in men.

statista.com/statistics/110…
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In Italy in particular, men seem to be dying of covid19 at a higher rate as well:

Men = 7.2% mortality
Women = 4.1% mortality

epicentro.iss.it/coronavirus/bo…
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Why would this be?

Some possibilities include that men and women seem to have different types of immune responses, levels of cardiovascular disease, even hand washing habits.

nytimes.com/2020/03/20/hea…
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Another major difference between men and women is the rate of cigarette smoking.

Men smoke more frequently than women in general, including in Italy and China.

worldpopulationreview.com/countries/smok…
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On a simple level, smoking involves repetitive hand-to-face movements, which could put smokers at higher risk of contracting the virus.

This association is conjectural but plausible.

blogs.bmj.com/bmj/2020/03/20…
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It's also established that smoking:

🔹Impairs immune responses in the lung
🔹Contributes to preexisting lung diseases/severity like asthma and COPD
🔹Associates with comorbidities like heart disease that increase the risk of death from covid19

ncbi.nlm.nih.gov/pubmed/32171067
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For these reasons, if more men smoke, then perhaps that contributes to their risk of covid19 infection and severity.

But that may not be the whole story...
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For reasons you'll see, let's take a closer look at Angiotensin Converting Enzyme II (ACE2):

🔹ACE2 is a peptidase on the surface of type 2 pneumocytes
🔹Covid19 binds it w/ high avidity

💥ACE2 is the receptor that allows covid19 to infect the body

ncbi.nlm.nih.gov/pubmed/32075877
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A logical question:

Does smoking affect ACE2 (eg covid19 binding site) levels in the lung?

💥Preliminary data suggests that smokers do express higher levels of lung ACE2.

In effect, more smoking = more covid19 receptor

mdpi.com/2077-0383/9/3/…
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This pre-publication report found no differences in baseline lung ACE2 expression between genders but did find higher levels of ACE2 in those who smoke.

medrxiv.org/content/10.110…
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One last point:

How vaping or marijuana smoking affects ACE2 levels in the lung is unknown.
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Let's summarize:

🔹There's a gender difference in covid19 infections/severity (men > women)
🔹Different smoking rates may account for some of this gap
🔹Covid19 binds ACE2 when infecting the airway
🔹Smoking increases ACE2 levels, ? increasing susceptibility to infxn
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