Infections such as cold, flu and chest infections are generally more common in the winter. One traditional explanation for this is that when the weather is cold, people spend more time indoors. The more time people spend with each other in close confinement, the more likely they are to catch something, as well as pass an infection to someone else.
This explanation almost certainly has merit, but it’s unlikely to be the whole story either. In recent years some scientists have suggested that the upsurge in infections seen in the winter may be due to lower levels of vitamin D. Vitamin D, among other things, facilitates the production of ‘anti-microbial peptides’. As their name suggests, these natural substances work like natural antibiotics to counter infecting organisms.
Prior to the advent of antibiotics, sufferers of tuberculosis might be sent to a sanatorium for rest, recuperation, and a healthy dose of sunshine. It is possible the when individuals recovered from their infection in this setting, at least some of this had to do with the higher levels of vitamin D they would have attained by taking in more sun.
I was interested to read about a recent study in which the relationship between vitamin D levels and ‘respiratory infections’ in 6,789 British adults . The researchers, from University College London, found that vitamin D levels and infection risk had a linear relationship, which in this case meant that the higher levels of vitamin D were, the lower the risk of infection.
For each 10.0 nmol/l (4.0 ng/ml) increase in vitamin D (25-hydroxyvitamin D), risk of infection was 7 per cent lower. There was a similar relationship with lung function too, with higher vitamin D levels being associated with better lung function.
I have previously reported on another study which found higher levels of vitamin D were associated with reduced risk of flu and reduced duration of the illness should they get it.
These studies are epidemiological in nature, and therefore cannot be use to conclude that vitamin D prevents infections. However, there is at least a plausible mechanism through which vitamin D might do this. We also have this study which found that vitamin D supplementation had some ability to reduce risk of flu in children.