Vitamin D, the 'sunshine vitamin', is one of the most important nutrients in protecting us from the virus.
Researchers have discovered a direct link between severe vitamin D deficiency and deaths from the virus. The association is clear in almost every country, but it's especially strong among people living in Italy, Spain and the UK, where COVID-19 deaths have been high.
A research team from Northwestern University believe vitamin D levels could explain the wide differences in mortality rates around the world, and it may have more to do with the level of deaths than factors such as healthcare quality, age distributions or testing facilities.
The healthcare system in northern Italy is one of the best in the world, and yet it saw some of the highest death rates, the researchers point out.
Vitamin D is an important regulator of the immune system, and it's an over-reaction to the virus—called a cytokine storm—that is killing people rather than the virus itself. The vitamin keeps the immune system in check and stops it from over-reacting to a threat.
This could also explain why children—whose immune systems are still developing—are not as badly affected by COVID-19.
A healthy vitamin D level could halve the death rate, says Vadim Blackman at Northwestern.
As well as sunbathing, we can top up our levels of the vitamin by taking supplements or eating oily fish or cod liver oil.