From Gerben Wierda, Heerlen, The Netherlands
You report on the beneficial effect of vitamin D on the innate immune system, our defence against primary infection with viruses such as the coronavirus (28 March, p 44). Research has shown that vitamin D protects against viral infections of the upper respiratory tract.
Might this, rather than temperature, be the main reason why such infections trail off in the summer months? Summertime is also when we produce the most vitamin D because there is more sunlight and we spend more time outdoors.
