I looked at covid and BMI in a post linked here. Using data from UK critical care units, it seems that BMI from 30-40 is only a small risk, though the risk from BMI>40 is substantial. This is after adjusting for age and sex.
A more recent UK study here found increased risk of death, after adjusting for age and sex, for obesity (BMI>30), and a substantially higher risk for BMI>40. These risks went down a bit when also adjusting for other factors. (Though depending on your purpose, this may not be valid, since some of these factors might be on the causal path from obesity to risk of death.)
You’re saying that obesity matters mostly if you’re younger than 60, which is a question not directly addressed by these results (which come up with a single risk ratio, on the assumption that it’s the same for all ages). The study here which you link to gives a scatterplot of BMI versus age in covid patients, showing a negative correlation. This is not meaningful information without a corresponding scatterplot for the general population from which these patients came, which they oddly do not show (or even speculate about, if data is hard to find). In that scatterplot, patients with really extreme obesity (BMI>50) seem to play a large role.
In my post, I present evidence that low BMI may be a risk factor, perhaps not only for BMI below the official “underweight” threshold of BMI<18.5 but also for around BMI<20. Frustratingly, many studies do not present the data that would allow one to investigate this. For the recent UK study I linked above, they use “not obese” as their reference class, grouping everyone with BMI<30 together, though their raw, unadjusted, data indicates that there is a substantial firsk for BMI<18.5 (and even in that data, they group everyone with BMI from 18.5 to 24.9 together, even though past studies show that there may be substantial differences within this supposedly “normal” range).
When looking at varying effects by age, one possibility to consider is that high BMI is a risk factor for younger people, and that low BMI is a risk factor for older people (as opposed to BMI not mattering for older people, as you sort of conclude).
I looked at covid and BMI in a post linked here. Using data from UK critical care units, it seems that BMI from 30-40 is only a small risk, though the risk from BMI>40 is substantial. This is after adjusting for age and sex.
A more recent UK study here found increased risk of death, after adjusting for age and sex, for obesity (BMI>30), and a substantially higher risk for BMI>40. These risks went down a bit when also adjusting for other factors. (Though depending on your purpose, this may not be valid, since some of these factors might be on the causal path from obesity to risk of death.)
You’re saying that obesity matters mostly if you’re younger than 60, which is a question not directly addressed by these results (which come up with a single risk ratio, on the assumption that it’s the same for all ages). The study here which you link to gives a scatterplot of BMI versus age in covid patients, showing a negative correlation. This is not meaningful information without a corresponding scatterplot for the general population from which these patients came, which they oddly do not show (or even speculate about, if data is hard to find). In that scatterplot, patients with really extreme obesity (BMI>50) seem to play a large role.
In my post, I present evidence that low BMI may be a risk factor, perhaps not only for BMI below the official “underweight” threshold of BMI<18.5 but also for around BMI<20. Frustratingly, many studies do not present the data that would allow one to investigate this. For the recent UK study I linked above, they use “not obese” as their reference class, grouping everyone with BMI<30 together, though their raw, unadjusted, data indicates that there is a substantial firsk for BMI<18.5 (and even in that data, they group everyone with BMI from 18.5 to 24.9 together, even though past studies show that there may be substantial differences within this supposedly “normal” range).
When looking at varying effects by age, one possibility to consider is that high BMI is a risk factor for younger people, and that low BMI is a risk factor for older people (as opposed to BMI not mattering for older people, as you sort of conclude).