An observational study published in the British Journal of Dermatology compared recorded deaths from Covid-19 in the US between January and April 2020 with local light levels.
It found that people living in areas with the highest level of exposure to UVA rays - which makes up 95 per cent of the sun’s UV light - had a lower risk of dying from Covid-19 compared with those with lower levels. The analysis was repeated in England and Italy with the same results.
The researchers took into account factors known to be associated with increased exposure to the virus and risk of death such as age, ethnicity, socioeconomic status, population density, air pollution, temperature and levels of infection in local areas.
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The reduction in risk of death could not be explained by higher levels of vitamin D, the experts said, as only areas where the level of UVB light was too low to produce significant vitamin D were included.
As the study was observational, it cannot determine a causal effect between sunlight and fewer deaths. But researchers are now looking into the area further.
One possible explanation for the lower number of deaths is that sunlight exposure causes the skin to release nitric oxide, which has been found in some lab studies to reduce the ability of SARS Coronavirus2 – the cause of Covid-19 – to replicate.
Previous research from the same group has shown that increased sunlight exposure is linked to improved cardiovascular health, with lower blood pressure and fewer heart attacks. As heart disease is a known risk factor in dying from Covid-19, this could also explain the latest findings.
Dr Richard Weller, corresponding author, consultant dermatologist and Reader at Edinburgh University, said: “There is still so much we don’t understand about Covid-19, which has resulted in so many deaths worldwide. These early results open up sunlight exposure as one way of potentially reducing the risk of death.”
Co-author and Chair in Health Geography Professor Chris Dibben said: “The relationship between Covid-19 mortality, season and latitude has been quite striking, here we offer an alternative explanation for this phenomenon.”