The researchers found "high mortality rates only in countries where overweight prevalence exceeds around 50% of the adult population."
"Globally, at the end of 2020, COVID-19 mortality rates were more than ten times higher in countries where overweight prevalence exceeds 50% of adults (weighted average 66.8 deaths per 100,000 adults) compared with countries where overweight prevalence is below 50% of adults (weighted average of 4.5 deaths per 100,000 adults)," the World Obesity Foundation wrote.
The researchers claimed that a country's wealth, reporting capacity, elderly population, and other factors could not explain the link between COVID-19 and obesity.
The United States has one of the highest obesity rates in the world, increasing from 30.5% to 42.4% of the population in the last 18 years, according to the CDC. The United States also has the 9th highest COVID-19 death rate in the world at 158.43 deaths per 100,000 people, according to Johns Hopkins University.
The CDC notes that obesity may triple the risk of hospitalization due to COVID-19, as it causes impaired immune function and can decrease lung capacity.
There are some exceptions to the World Obesity Foundation's findings, as countries like New Zealand, Australia, and some Gulf states have relatively high obesity rates but low death rate from COVID-19.
"These figures are clearly affected by national responses to the COVID-19 pandemic, and will change as the pandemic unfolds and as vaccination programmes are extended," the researchers wrote.
But there is some evidence that the vaccines currently rolling out around the world are less effective in obese people.
Researchers at the National Cancer Institute Regina Elena in Rome found in a study on the preprint server Medrxiv, which is yet to be peer-reviewed, that obese people produced notably fewer antibodies after being vaccinated than those with a normal body weight.