Vitamin D deficiency, obesity, co-morbidities, and extensive treatment of Covid-adjacent conditions - the real drivers?

Just a speculative hypothesis:  the mortality rate of Covid-19 is a function of:

• Co-morbidities

• Obesity

• Vitamin D deficiency

• and prevalence of treatments for Covid-adjacent infections 

Except where there has been obvious policy incompetence, such as housing Covid-19 patients among the elderly in retirement communities, there has been little clarity regarding why there are such significant variances in death rates between countries.  In particular, deaths in developing countries are far lower than originally forecast.

The media and some researchers have focused on age as an explanatory variable - the older the population, the higher the death rate.  However, it is my sense that that is a confusion between first and second order variables.  Age may be highly correlated with elevated Covid-19 death rates but Age is also highly correlated with co-morbidities.

My intuition is that Age itself may not be the real driver here.  Co-morbidities are.  

Vitamin D deficiency keeps popping up as key variable in numerous studies.  Ad does obesity.

More speculative still, it seems like there is emerging evidence that countries with relatively high pathogen or high viral loads seem to have lower death rates for Covid-19.  These tend to be countries in the tropics.  There could be three different causal pathways, or possibly both.  

Tropical countries where there are high pathogen or high viral loads may have populations which are simply more primed to resist Covid-19.  Such countries may have a greater prevalence of viruses sufficiently similar to Covid-19 to provide some protection.  Such countries may have a higher population with exposure to treatments for other diseases which are also effective at reducing the lethality of Covid-19.

On the latter point, this testimony from Peter McCullough, MD testifies to Texas Senate HHS Committee is probably relevant.  Dr. McCullough has two main arguments:

First, by focusing almost exclusively on flattening the curve and investing in developing a vaccines, nearly abandoned any structured pursuit of treatment of the Covid-19 condition.  

Second, while there has been a lot of incidental small scale research on treatment, the results have been modest.  Any single treatment, such as hydroxychloroquine,  may have ambivalent or only mild effect sizes.  There has been no silver bullet treatment so far discovered

However, combinations of these low effect size treatments can cumulatively have very material effect sizes and dramatic reductions in bad outcomes.  He likens this to the treatment of HIV where it is the cocktail, not the individual components which provide the effective treatment.

If this hypothesis (Vitamin D deficiency, obesity, co-morbidities, and extensive treatment of Covid-adjacent conditions) proves out, it has numerous implications.  Vitamin D deficiency is cheap and easy to treat.  Obesity is not especially easy but it is certainly treatable.

Co-morbidities are more challenging because they often are the cumulation of a lifetime's behaviors and decisions.  But if co-morbidities are indeed as predictive as I suspect, then interventions such as isolation or other such approaches can be far more targeted.  

Perhaps the highest return would be additional attention to and more structured research in treatment cocktails which have the promise of dramatically reducing loss of life at a relatively low cost.

We are a number of years away from understanding the nature of and course of Covid-19 but I suspect we are going to discover a lot more lives could have been saved had we a clearer picture of the true drivers of the death rates.