Once upon a time, vitamin D was associated exclusively with bone health and development; those of you who aren’t exactly spring chickens might remember being force-
fed cod liver oil by well-meaning parents.

Vitamin D is still as important as ever for building strong and healthy bones, but scientists are beginning to realise that the role of vitamin D in promoting and sustaining human health goes far beyond bone metabolism. An area of particular interest is immunity.

In the last couple of years, studies have shown that your vitamin D status is crucial for normal immune function. And now a new study suggests that optimum vitamin D intake could be even more important for cyclists wishing to keep winter coughs and bugs at bay!

The science
In the study, British scientists from the Universities of East Anglia, Loughborough and Nottingham gathered together 225 subjects who were engaged in regular endurance sports training such as cycling, running, swimming, triathlon, etc.

These subjects ranged from recreationally active ‘weekend warriors’ to Olympic triathletes, and their self-reported training loads averaged 10 hours per week.

The goal of the study was to determine the influence of the athletes’ vitamin D status on their immune function and the incidence, severity and duration of upper respiratory tract illness (URTI – coughs, colds, sore throats, sneezing, earaches, nasal congestion fever, chills, etc) episodes over the course of a four-month winter training period.

To achieve this, the athletes completed daily URTI symptom diaries and reported their weekly training loads using carefully validated questionnaires. The researchers also collected blood samples from the athletes at the start and end of the study to measure vitamin D status, and saliva at the start of the study, repeating at four-weekly intervals to measure markers of immunity.

In a nutshell
At the start and end of the study, 38 per cent of the athletes had inadequate blood vitamin D (less than 50 nanomoles per litre), while 55 per cent had deficient levels of blood vitamin D (less than 30nmol/L).

Intriguingly, a significantly higher proportion of subjects in the vitamin-D-deficient status group came down with an URTI during the four-month study period compared to the optimal vitamin D group (120nmol/L or more).

Moreover, the total number of ‘URTI symptom days’ and the symptom-severity score in the vitamin D deficient group was significantly higher than in the other groups. When the researchers looked at markers of immunity, they found that the levels of antibodies that help defend the cells of the nose, throat against viruses in the optimal vitamin D status group was significantly higher than in the other groups and that a low vitamin D status was associated with lower levels of immune proteins, which stimulate immune defences against bacteria and viruses.

So what?
Compared with low-vitamin-D status endurance athletes, those with high levels of blood vitamin D had fewer episodes of URTI, less severe symptoms when they did occur, and greatly improved levels of immune markers.

This study is important because it’s the first to show that optimum vitamin D status in athletes such as cyclists undergoing vigorous training can boost immunity. And because it used a large number of subjects from a range of sports, its findings are likely to be valid and widely applicable.

In short, this study adds to a growing body of evidence that boosting your vitamin D intake through the winter months (when we have insufficient sunlight exposure) is a worthwhile strategy to keep winter bugs at bay.

Exerc Immunol Rev. 2013;19:86-101

This article was first published in the December 19 issue of Cycling Weekly. Read Cycling Weekly magazine on the day of release where ever you are in the world International digital edition, UK digital edition. And if you like us, rate us!

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