Are global coronavirus death rates linked to a country's obesity levels?

The coronavirus has spread steadily among the world’s wealthiest nations with some of the worst hit – including the UK and the the US – also struggling with widespread obesity problems.

Now prime minister Boris Johnson is expected to introduce measures to limit supermarket deals on junk foods in a bid to reduce rates of obesity – a U-turn on his previous opposition to the government interfering with people’s diets, according to The Times.

The PM is said to be privately convinced his weight led to the severity of his own near-death experience with the virus.

Meanwhile an editorial written by researchers at Queen Mary University of London and published in the British Medical Journal last month argued the food industry must take its share of the blame “not only for the obesity pandemic but also for the severity of Covid-19 disease and its devastating consequences”.

But can a national obesity problem go some way towards explaining a high coronavirus death rate?

The science

While scientists have had to work rapidly to respond to the pandemic since Covid-19 emerged, the links between obesity and a severe Covid-19 infection have been well established over the past nine months.

In one French study looking at patients at Lyon University Hospital which was published in The Lancet, those with a severe case of the virus were 1.89 times likely to be obese than the general population.

A US study published in the same journal found an average BMI among test subjects of 29·3 – just on the edge of the classification for obesity. There was also a trend – the younger a person hospitalised with Covid-19 was, the more likely they were to be obese.

Meanwhile those who are obese are more likely to have a number of underlying health conditions that have proven particularly dangerous for a coronavirus sufferer – such as diabetes and chronic heart, kidney and liver diseases.

However it starts to get more difficult when comparing fatalities in different countries.

The global picture

While obese people are disproportionately affected by the virus – and 44 per cent more likely to have a critical case in the UK according to a letter published in the British Medical Journal – the amount of other mitigating factors make it hard to pin weight down as a definite culprit.

According to the latest WHO data from 2016, around 39 per cent of the global population is overweight and 13 per cent are obese. And the 30 worst afflicted nations when looking at deaths per 100,000 as assessed by Johns Hopkins University all have a population where more than 50 per cent of the population is classified overweight.

Meanwhile nations with lower rates of death per 100,000, such as Japan, Bangladesh and South Korea, are all less overweight nations than the global average.

Overall those nations where more than 50 per cent of people are overweight carry an average death per 100,000 figure of 12.58 – compared to a rate of 1.14 in nations where fewer than 50 per cent are overweight.

But there are plenty of outliers – and while the way virus deaths and cases are recorded has impacted comparisons between nations, the way individual nations have responded to the virus, the age of its population and the strength of its healthcare system also make it hard to spot trends.

New Zealand is among the world’s most obese nations, but managed to limit the spread of infection through an early lockdown and has now emerged almost entirely with stringent border controls and double digit case numbers.

And while the rate of obesity in India is steadily growing, it still remains low with only 19.7 per cent of population classified as overweight – however the country has seen 1.6 deaths per 100,000 as a result of Covid-19 – putting it in the middle of the pack when it comes to fatalities by the metric.

Meanwhile in some wealthy nations like the UK and the US where nutritionally poor, high energy foods are often cheaper, there is an overlap between poverty and obesity – with the complicated issues which cause poverty also leading to worse health outcomes.