Covid-19 and Obesity

This report shows that in countries where less than half the adult population is classified as overweight [BMI > 25 kg/m2], the likelihood of death from COVID-19 is a small fraction – around one tenth – of the level seen in countries where more than half the population is classified as overweight. Of the 2.5 million COVID-19 deaths reported by the end of February 2021, 2.2 million were in countries where more than half the population is classified as overweight.

from Covid-19 and Obesity: The 2021 Atlas, World Obesity Federation, released March 2021

The report cites several studies, conducted in various countries, demonstrating that overweight and obese people are more susceptible to severe covid infections, including hospitalization, admission to the ICU, and death. These studies find that overweight people are two to three times as vulnerable to severe covid as are non-overweight people. That makes sense: covid severity is associated with a variety of comorbidities, including heart disease, hypertension, and diabetes, that are more prevalent among the overweight and obese. Obesity has also been shown to compromise the immune response to infection.

Extrapolating from these studies, one might expect that a country in which everyone is overweight would experience a covid fatality rate two to three times as high as a country in which no one is overweight. However, the Covid-19 and Obesity report found a tenfold increase in the odds of dying from covid for countries in which “only” half the population is overweight compared to countries with fewer than half of its people being overweight. Almost certainly some other factors in addition to BMI must account for these inter-national comparisons.

Age has been shown to be a huge predictor of covid fatality, more dramatic by far than the reported differences based on overweight. E.g., the CDC reports that Americans aged 50 to 64 are ten times as likely to die of covid as are those aged 30 to 39. Looking at the Covid-19 and Obesity report’s maps, most of the countries with low percentages of overweight people also have populations with a low median age. Per the report:

The figures are affected by the age structure of national populations and a country’s relative wealth and reporting capacity, but our findings appear to be independent of these contributory factors. Furthermore, other studies have found that overweight remains a highly significant predictor of the need for COVID-19 health care after accounting for these other influences.

An “independent and highly significant predictor”: how much of the between-countries differences in covid mortality can be attributed to overweight, independently of age? According to the report, percent overweight accounts for about a third of the variance in covid mortality when looking separately at countries with low, medium, and high percentages of the population above age 65. That’s sort of informative. However, the authors could just as easily have conducted the same analysis for age as they did for overweight, arriving at a statistical estimate of the relative odds of covid death for old versus young countries. I’d expect that difference to be even more stark than the relative odds of high versus low overweight. Still, it seems plausible based on the research that overweight would account for up to a twofold difference in covid mortality rates between countries, independent of age.

Looking at the report’s maps, nearly all of the countries with low overweight percentages are in Asia and Africa, while nearly all of the high-overweight countries are in Europe and America. That’s true for age as well: most of the countries with young populations are in Asia and Africa. What we need is a multivariate model looking at the across-countries correlations among median age, median BMI, covid infections and deaths per 100K population…

 

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