Can Lack of Obesity Explain Low COVID-19 Death Rates in East Asia?

An unresolved puzzle of the pandemic is why COVID-19 death rates have been so low in East Asia. We know this can’t be due to different ways of counting COVID-19 deaths because it shows up in comparisons of excess mortality.

The most recent published estimates of excess mortality, taken from a paper in eLife by Ariel Karlinsky and Dmitry Kobak, are shown below. In this analysis, excess deaths since the start of the pandemic are given as a percentage of annual baseline mortality (see grey numbers).

Excess mortality in Europe ranges from –4% in Norway to 43% in North Macedonia, and most countries are in the 10–30% range. In East Asia, by contrast, excess mortality ranges from –11% in Mongolia to 4% in Hong Kong. (Note: excess deaths in East Asia may have increased slightly in more recent months.)

As I’ve argued before, it’s unlikely this difference is due to lockdowns as Japan has seen negative excess mortality despite having some of the least restrictive policies in the world. In 2020, for example, there were zero days of mandatory business closures and zero days of mandatory stay-at-home orders.

So what can explain East Asia’s low COVID death rates? One factor that’s often mentioned on social media is their low rates of obesity. As I’ll explain, however, this can’t explain more than a small part of the difference between East Asia and the rest of the world.

To begin with, obesity’s effect on the risk of death from COVID-19 – conditional upon on infection – is actually quite modest. (By comparison, the effect of age is enormous.)

While it’s often said that most COVID-19 patients in the U.S. are overweight or obese, this is isn’t very surprising. After all, most U.S. adults are overweight or obese. For example, a CDC study published in March found that 50.8% of COVID-19 patients were obese. Yet the figure for adults as a whole is only slightly lower, at 42.4%.

Earlier this year, the BBC radio program More or Less (which deals with statistics in the news) calculated that if the global obesity rate dropped to zero, the total number of COVID-19 deaths would fall by only 7%.

If you look at the chart above, there is no obvious clustering of highly obese countries on the first two rows. For example, the obesity rate in Peru – which has seen excess mortality of 153% – is less than one in five.

What’s more, two recent studies estimated that there have been around 4 million excess deaths in India. This equates to excess mortality of around 40%, which would place India on the top row of the chart above. Yet the country has an obesity rate of only 3.9% – one of the lowest in the world.

All this suggests that something other than lack of obesity explains the low COVID-19 death rates in East Asia.

Stop Press: For an alternative view on the relationship between obesity and COVID mortality, see this post on Swiss Policy Research.