Lots of Surprises

Biology Methods and Protocols 9:1 (2022) did a really large survey of Czechs and looked for behaviors, physical traits, and dietary supplements to see if there was an association with risk of COVID-19 infection and severity once infected.  Many of the results are surprising:

Blood group (system ABO) had a moderate effect on the risk of COVID-19 infection and probably no effect on its course. Individuals with blood group 0 had a lower and those with blood group B had a higher risk of infection. The former concurs with the majority of published findings [24, 25]. The higher risk of the infection in subjects with blood group B also agrees with published data, but a meta-analytic study showed that blood group A usually has a stronger effect on the risk of COVID-19 than blood group B does [26]. Both effects were stronger and statistically significant in men, while in women, they were weaker and nonsignificant. In the second questionnaire, men with blood group B reported worse physical health, while those with blood group 0 reported better physical but worse mental health.

There is an enormous variation in blood types by ethnicity.  It makes you wonder how severe the national variations in infection and death rates might be tied to this.  U.S. blacks are 20% B; U.S. whites are 11% B.  Sweden did very well with a much less severe approach to the disease; they are also only 10% B.

Rh factor had no significant effect on the risk of infection. Rh-positivity had only nonsignificant effects on the severity of the course of COVID-19 (significant for the severity of symptoms index in men), which concurs with previously published data [26]. Similarly, Rh-heterozygosity had no significant effect on the risk or severity of COVID-19, but that could be due to the relatively low number of participants whose heterozygosity could be determined based on their Rh-phenotype and the Rh-phenotype of their parents. Our results indicate that the potential effects of the Rh-factor on the risk and severity of COVID-19 do deserve further attention. However, the investigation of this phenomenon should be preferably based on DNA-genotyped populations because Rh-positive heterozygotes have better health and Rh-positive homozygotes have worse health than Rh-negative individuals [12]....

Many behavioral traits had protective effects against the infection, while three factors, namely being actively involved in sport (in both men and women), frequent singing (only in men), and cold water swimming (in both men and women), increased the risk of infection. We can only speculate about the proximal reasons for these findings. It seems likely that these activities increase the risk of infection only indirectly, that is, by increasing the number of physical contacts with other people. It is, however, also possible that singing facilitates the transmission of the virus even directly. A large community-based cohort study performed on 387 109 UK citizens showed a positive effect of physical inactivity on the risk of COVID-19. However, the study took into account only hospitalized patients and not the numerous subjects without a severe course of COVID-19 [28]. The negative effect of sport on the risk of hospitalization thus probably reflects the negative effect of physical activity on the risk of severe COVID-19 (also observed in our study) rather than its negative effect on the risk of the SARS-CoV-2 infection.

The most substantial protective factor against COVID-19 infection was strict adherence to wearing masks and respirators; this factor was stronger in men than in women. Based on the results of laboratory tests, it is usually supposed that the wearing of masks, and even more so respirators, protects individuals against infection with SARS-CoV-2 (and not only against transmitting the infection to other people). On the other hand, the results of a meta-analytic study show that empirical evidence for this claim is relatively weak [29]. To the best of our knowledge, there is no published prospective longitudinal study that examined the effects of wearing masks on the risk of COVID-19 or its severity (up to October 2021).

Curious that they observe that with regard to masks "On the other hand, the results of a meta-analytic study show that empirical evidence for this claim is relatively weak..."  All that shaming and virtue signaling over something which seems to be effective but for which the evidence is weak.

The second most substantial protective factor was the consumption of vitamins and supplements. Analyses performed separately for women and men had shown that the strongest protective factor in women was walking in nature, possibly an indication of a solitary activity of more introverted women, because in men, walking in nature was a risk factor, albeit a weak and nonsignificant one, rather than a protective factor. The strongest protective factor for men was adherence to wearing masks and respirators. Sustaining social distance and frequent washing hands had only a weak and nonsignificant effect in both men (P > 0.069) and women (P > 0.699).

Again,  "weak and nonsignificant" protective factors on two highly hyped behaviors: social distancing and frequent hand washing.  Vitamin D turned out to be a significant factor in reducing infection risk.

We found that tobacco smoking (in both men and women) and partly also marihuana use (in women) have a relatively strong protective effect against SARS-CoV-2 infection. Marihuana use and, less probably, tobacco smoking could also have some protective effects against a severe course of COVID-19. The protective effects of tobacco smoking have been reported [7] and discussed [30] in some previous studies. However, most studies show adverse effects of smoking on the risk of a severe course of COVID-19 [2, 19, 28, 31, 32]. The former smoking habit seems to have three times stronger adverse effect than current smoking [33]. This result agrees with that of a meta-analytic study based on 233 studies [7]. We have no explanation for the contradiction between our data and reported data except for a hypothetical publication bias: it is possible that authors and editors may be reluctant to publish results showing any positive effects of smoking. It should be mentioned, though, that in our study, smokers reported worse mental health, and female smokers reported worse mental and physical health in the second questionnaire than nonsmokers did.

This is the biggest surprise to me, unless smoking creates an unfavorable environment for COVID-19.  Still not a good reason to smoke. 

The most unexpected result of this part of the study was the positive correlation between higher severity of the course of COVID-19 and adherence to wearing masks and respirators and, to a lesser extent, also with keeping social distance. We speculate that individuals with predispositions to a severe course of COVID-19, mainly those who were overweight, suffered immunodeficiency, COPD, or diabetes, put more effort into trying to avoid infection and more strictly adhered to recommendations concerning wearing masks and maintaining a safe distance. At the same time, if they did become infected, they had a more severe course of the disease than individuals without such risk factors. The strength of these associations was lower or nonexistent when the intensity of symptoms or duration of COVID-19 was used as a measure of the severity of COVID-19 (except for the rather strong association between maintaining safe distance and duration of COVID-19 in women). Also, it was much stronger when we used a self-rated severity of the course of COVID-19. It is possible that subjects who did not adhere to recommendations concerning personal protection against COVID-19 were later more reluctant to admit that they had a severe course of the disease. Alternatively, one could also speculate that more anxious people followed existing recommendations concerning personal protection against COVID-19 more strictly, but they also tended to have a more severe course of COVID-19 if they did become infected. On the other hand, the strength of all the associations remained approximately the same when we included in the model the reported intensity of anxiety and depression (partial Tau: masks 0.105 versus 0.109; distance 0.107 versus 0.107).