Linda Geddes writes:

For the past two months, a sizable chunk of the world’s population has been shuttered inside their homes, only stepping out for essential supplies. Although this may have reduced our chances of being exposed to coronavirus, it may have had a less obvious effect on our immune systems by leaving us more vulnerable to other infections.

Humans evolved on a planet with a 24-hour cycle of light and dark, and our bodies are set up to work in partnership with sunlight. One of the most obvious examples of this is the production of vitamin D in the skin in response to UVB exposure. This daily dose of vitamin D can help to strengthen our bones and teeth, but it also has an effect on our immune cells.

Vitamin D enables the macrophages in our lungs – a first line of defence against respiratory infections – to spew out an antimicrobial peptide called cathelicidin, killing bacteria and viruses directly. It also tweaks the activity of other immune cells, such as B and T cells, which orchestrate longer-term responses. People with low levels of vitamin D are at greater risk of viral respiratory tract infections such as influenza.

Researchers are now investigating whether vitamin D supplements could even reduce the risk of some of the severe complications associated with Covid-19. Earlier this month, Rose Kenny, a gerontologist at Trinity College Dublin, and her colleagues published data suggesting that European populations with the highest death rates from Covid-19, including Spain and Italy, have the lowest levels of vitamin D. This may sound counterintuitive, given their sunny climates, but it is thought that changes in lifestyle have led people to spend more time indoors, which combined with greater use of sunscreen in these countries, may be responsible for the lower levels of vitamin D. [Continue reading…]