Vitamin D is also involved in immune response, and in population studies, low levels of vitamin D have been linked to an increased risk of upper respiratory tract infections. Indeed, outbreaks are more common in winter when vitamin D levels get lower. “Vitamin D supplementation has been shown to prevent upper respiratory tract infections among those with significant vitamin D deficiency. For this purpose, a dosage of 20 micrograms per day has been sufficient, and higher doses have not provided any additional benefit.”
During the past year, a lot of studies have addressed the association between vitamin D status and the risk of COVID-19. “In Europe, the COVID-19 situation has been among the worst in Spain and Italy where low serum levels of vitamin D are common. In these countries, there’s plenty of sunshine almost all year round, but sun exposure is avoided, and as no foods are fortified with vitamin D, intake from food is low. In Finland, on the other hand, both the population’s vitamin D levels and the COVID-19 situation are among the best in Europe. Of course, there are other differences between countries that can affect the situation as well, such as differences in housing density and health care capacity,” Virtanen says.
A pilot study carried out in Spain showed that vitamin D supplementation could help to prevent severe forms of COVID-19. Among patients hospitalised with COVID-19, those who were given 25-hydroxyvitamin D, also called calcidiol, which is the storage form of vitamin D in the body, were less likely to need intensive care. “This small-scale study has been followed by a larger trial, the results of which are yet to be published.”
As Virtanen points out, there is yet no evidence that vitamin D supplementation could prevent you from contracting the virus. In any case it’s reasonable to ensure proper intake, given the role of vitamin D in the immune system.
In Finland, the Helsinki and Uusimaa Hospital District (HUS) has issued its own vitamin D recommendations to prevent severe COVID-19. HUS recommends 20 micrograms per day for everyone over 70 and in assisted living as well as for dark-skinned adults. In these groups, obese persons with a body mass index of 30 or more are recommended a dose of 50 micrograms per day. This is due to the fact that vitamin D is stored in adipose tissue and hence obesity reduces the availability of vitamin D in the body.
“In addition to obesity, many other risk factors of severe COVID-19, such as higher age, sedentary behaviour, diabetes and other chronic diseases are associated with lower vitamin D levels. From this perspective, low levels of vitamin D might not be such an important risk factor in itself, but rather a marker of these other risk factors. It can also be the result of coronavirus infection instead of being the cause, because infection lowers vitamin D levels in the body.”