Vitamin D and the athlete: what it can really do for you

Of all the nutrients required for human health, it is without doubt vitamin D that has attracted the most attention over recent years. This perhaps is hardly surprising; although the importance of vitamin D for bone health has long been understood, more recent evidence has demonstrated that optimum intakes of vitamin D in adults (either through diet, supplements or sun exposure [where vitamin D can be synthesized in the skin]) provides significant protection from age-related degenerative diseases such as heart disease, multiple sclerosis and a number of different cancers^(1,2).

Winter and vitamin D

Perhaps even more relevant for athletes training in mid winter (in the northern hemisphere at least), the data is now conclusive that your vitamin D status is intimately linked to your immune function. In a nutshell, a sub-optimum vitamin D status harms immunity, whereas an optimum vitamin D intake improves immunity.

A 2019 systematic review study (pooling the data from 14 other studies on vitamin and immunity) found that the lower the level of vitamin D in the blood, the higher the risk of an acute and severe respiratory tract infection (including covid-19⁽³⁾ – see figure 1), and the more severe it was likely to be – especially when levels of vitamin D in the blood dropped below 37.5ng/L⁽⁴⁾.

Moreover, studies on athletes undergoing hard training have found conclusive evidence that a sub-optimum vitamin D status leads to more frequent, longer duration and more severe upper respiratory tract infections (URTIs - coughs, colds sore throats etc) compared to athletes whose vitamin D status is sufficient^(5,6), and that supplementing extra vitamin D during the winter months reduces the incidence and impact of URTIs⁽⁷⁾.

Figure 1: Vitamin D therapy and covid-19 outcomes*