This article was first published in The Montreal Gazette.
Let me be very clear. Smoking does not protect you from coronavirus. Neither does vitamin D. But recent reports have suggested that current smokers are less likely to die from coronavirus and that low vitamin D levels resulted in more severe infections. Neither assertion is really true.
The studies in question are interesting. The first one was a massive undertaking analyzing the health records of 17 million British patients. After analyzing all that data, researchers found that current smokers were less likely to die of COVID-19 than non-smokers or former smokers. Some people have suggested that this means that smoking might be protective against COVID-19 or that nicotine itself might have some protective properties. But there is a much more plausible explanation for the findings that doesn’t require us to abandon the idea that smoking is the worst possible thing that you can do to your body.
Why the researchers found this seemingly paradoxical result is interesting. First, what they measured is in-hospital mortality. So if smokers were more likely to die at home than non-smokers, they wouldn’t be counted and this would make smoking seem less dangerous. Also, one has to consider that smokers are more likely to die of something else. Since you can only die once, if you are more likely to die of heart disease, then you will be less likely to die of COVID-19. However, that doesn’t make smoking protective, it just makes it more dangerous in another way. Finally, consider that smokers who develop bad lung disease like Chronic Obstructive Pulmonary Disease are more likely to quit smoking in an effort to get better. Since lung diseases like COPD make it more likely that you will get complications from COVID-19, if the people with COPD are more likely to be ex-smokers than current smokers, that will make smoking seem protective.
Similar problems occur with the vitamin D studies. Some research has suggested that lower vitamin D levels are associated with more COVID-19 cases and more COVID-19 deaths. One interpretation is that vitamin D can boost the immune system and help fight off the infection. However, a lot of the vitamin D research is actually negative, which led me to declare in a recent column that 2019 had not been a good year for Vitamin D. In reality, it is very unlikely that vitamin D has any major non-skeletal health benefits and the current findings have another very plausible explanation. Older individuals tend to have lower vitamin D levels than younger individuals. This can happen either because older people do not go outside as much and have less exposure to UV light and therefore produce less vitamin D in their skin. The other possibility is that older people may have less comprehensive diets than younger people and may, therefore, become vitamin D deficient. Older people are also more likely to have kidney disease, and the kidney is necessary for converting vitamin D into its active form.
So, it may not be that low vitamin D levels make you sick, it may just be that the sickest patients have low vitamin D levels. We call this reverse causation, and it bedevils even the best research projects even when you try to adjust for it statistically.
The point here is that it would be nice if there was one simple thing we could all do to protect ourselves. Unfortunately, there isn’t. It probably won’t help if you take vitamin D and please, in the name of all that is holy, do not start smoking. Thankfully, there is a really easy thing you can do, that will absolutely help you to protect yourself: stay home and wash your hands.