Has obesity driven not just covid mortality, but the pandemic itself?
Several studies have shown that obese people not only have a higher covid fatality risk, but they also have higher viral loads, exhale more bioaerosols, and do so for a longer period of time. Thus, could obesity have driven not only covid mortality, but the pandemic itself? And could the near-absence of obesity in some East Asian countries explain their remarkable resilience against the covid pandemic?
Please note: This is a scientific analysis; it does not support “fat shaming”.
A) Covid mortality and age
The preferred framework for explaining covid mortality usually has been age: the older a person, the higher the infection fatality rate. The older the average age of a population, the higher, allegedly, covid mortality (assuming equal infection prevalence).
However, if one excludes the nursing home population in Western countries – which accounts for about 50% of Western covid deaths, but only about 1% of the overall population – the age-gradient of the covid infection fatality rate is actually much less steep than is commonly assumed (see the chart above).
Furthermore, if one excludes Western nursing homes, the covid IFR in the general population is in fact not that much different between, for instance, Europe, the US, South Africa, Latin America and India (about 0.2% to 0.5%).
In most countries, the median age of covid deaths is quite close to the average life expectancy of the country in question, e.g. 80+ in Western Europe, 78 in the USA, 70 in Brazil, and 62 in South Africa. Indeed, the young average age of many Latin American countries, South Africa or India has not at all protected these countries against high covid mortality rates.
It is well known that Sars-Cov-2 uses the ACE2 cell receptor, which is primarily a receptor of the endothelium and the cardiovascular system. Hence it is reasonable to assume that covid severity may be linked to cardiovascular and metabolic health, which is indeed the case.
Given this association, one may argue that the residual age-gradient of covid fatality rates in the non-nursing home population may be driven, to a significant extent, by cardiovascular and metabolic health. In addition, the status of being a nursing home resident may itself be closely associated with poor cardiovascular health and with general frailty.
It should be noted that many generally healthy people over 100 years of age, and up to 117 years of age, have already survived a covid infection, which may also speak against “age” as a paramount risk factor of itself. Indeed, among the five countries with the highest life expectancy in the world, we find Japan, South Korea and Singapore, all of which have very low covid mortality rates.
In conclusion, it may be argued that age, in itself, may not be the primary factor determining covid fatality rates. Instead, cardiovascular and metabolic health, of which obesity rates may be seen as a reasonable proxy value, should be considered.
B) Obesity and covid mortality
The above chart compares obesity rates in women (which are more pronounced than in men) to total excess mortality between March 2020 and May 2021. In most countries, excess mortality during the pandemic has primarily been driven by covid mortality (exceptions see below).
In many countries, high obesity rates are associated with high covid mortality rates. This includes the United States (36% obesity rate); most of Europe, in particular the UK (28%) and large parts of Eastern Europe (e.g. the Baltic states, Poland, Hungary, Czechia, Bulgaria; all 23% to 26%); Russia (23%) and Kazakhstan (21%); most of Latin America (including Mexico and Peru; 20% to 30%); South Africa (28%); as well as Turkey, Iraq and Iran (26% to 32%).
A few countries have high obesity rates, but low covid mortality rates. This group includes Canada, Australia and New Zealand (all 30%), and some Arab countries (notably Algeria and Saudi Arabia, at 28% and 35%). In the case of Canada, Australia and New Zealand, it is clear that these countries have managed to keep covid infection prevalence low due to strict border management; otherwise, their covid mortality would most certainly have been quite high. In the case of the Arab states, infection prevalence is not known, but the example of Bahrain (30%) indicates rather high mortality rates.
(Update: The latest edition of the Economist’s global excess mortality analysis shows that Saudi Arabia in fact has very high excess mortality, consistent with their very high obesity rate.)
Next, there are countries with a low obesity rate and a low covid mortality rate. Very significantly, the countries which proved to be highly resilient against the covid pandemic are also the countries with the lowest obesity rates in the world: Vietnam, Bangladesh, Cambodia, Japan, South Korea and Laos (all below 5%), Singapore, the Philippines and Indonesia (5% to 7%), and Thailand (10%), as well as many Black African countries (5% to 10%), but not South Africa (28%, see above).
Finally, there are a few countries with an apparently low obesity rate, but a not-so-low excess mortality rate. This group includes India and Nepal (both 4%) and some countries in central and eastern Africa (5% to 10%). However, a closer look into Indian obesity rates reveals that, while the national obesity rate is very low, it is in fact very high in urban areas (reaching 20% to 50%). While this ‘urban obesity effect’ may apply to some other countries, too, it seems to be particularly pronounced in India.
Nepal seems to be a real outlier; it has seen a major infection and mortality wave, but only in the spring of 2021, driven by the more infectious “Indian variant” of the coronavirus. Is the “Indian variant” perhaps more infectious than the original “Wuhan variant” because it is more infectious in non-obese people? Did Sars-Cov-2 get better at transmitting from lean people?
In the case of African countries with low obesity rates but elevated excess mortality, it is difficult to say if excess mortality was due to covid or due to other factors (e.g. hunger, tuberculosis, malaria).
In China, the national obesity rate is still low (6%), but reaches levels greater than 20% in some cities. Due to extreme Chinese lockdowns and a general lack of reliable prevalence and mortality data, it is difficult to say in which of the above groups China belongs.
In conclusion, it looks like obesity rates are indeed strongly associated with covid mortality rates. Most supposed ‘exceptions’ are easily explained. The biggest question marks concern some Arab states (notably Saudi Arabia, where infection prevalence is not known), Nepal, and China.
C. Obesity and covid infections
In addition to a higher fatality risk, studies have shown that people with obesity also have a higher viral load and do so for a longer period of time. It has been argued that this may be because of a higher concentration of ACE2 cell receptors in adipose tissue. Furthermore, studies have shown that exhaled bioaerosols increase with age and body mass index (BMI), as is shown in the chart above.
In sum, given that Sars-Cov-2 appears to be transmitted primarily via aerosols, and that pre-symptomatic transmission appears to play an important role (30% to 60% of all transmission), this could mean that obesity (and possibly excess weight in general?) could drive coronavirus infections, the frequency of “super-spreading” events, and the covid pandemic in general.
If so, this could explain why the countries with the lowest obesity rates in the world – such as Vietnam, Bangladesh, Cambodia, Japan, South Korea and Laos (all below 5%) – appear to have been exceedingly resilient against the covid pandemic, with a very low coronavirus infection prevalence, morbidity and mortality (although the new “Indian variant” might pose a challenge to them).
It could also explain why, in contrast, countries with high obesity rates have often seen very explosive, nation-wide outbreaks of coronavirus infections (e.g. in Latin America, in the US, and also in Eastern Europe in the autumn of 2020), followed by high covid morbidity and mortality.
Ironically, many Western countries assumed that the success of East Asian countries was due to face masks, only to find out that face masks have had no impact at all on coronavirus infection rates (as was already known from influenza epidemics).
The potential link between obesity rates and the rate of covid infections, morbidity and mortality should be further investigated in order to elucidate the dynamics of the coronavirus pandemic.
(See postscript below.)
Postscript: Obesity and influenza
Interestingly, a similar relationship between obesity and infectiousness was already found in the case of influenza:
“Why are obese patients potentially more contagious than lean subjects? Three factors make obese subjects more contagious than leans:
- First, obese subjects with influenza shed the virus for a longer period of time (up to 104% longer) than lean subjects, potentially increasing the chance to spread the virus to others .
- Secondly, the obese microenvironment favors the emergence of novel more virulent virus strains. This is due mainly to the reduced and delayed capacity to produce interferons by obese individuals and animals [17, 18]. The delay in producing interferon to contrast viral replication allows more viral RNA replication increasing the chances of the appearance of novel, more virulent viral strains .
- Thirdly, body mass index correlates positively with infectious virus in exhaled breath . This finding was especially significant for males, which leads to the hypothesis that the higher ventilation volumes or a differential chest conformation might explain this fact”
Source: Influenza and obesity: its odd relationship and the lessons for COVID-19 pandemic (Luzi & Radaelli, Acta Diabetologica, April 2020)