The study, which monitored 225 endurance athletes involved in regular intensive sports training such as cycling, triathlon, middle and long distance running or swimming, found that individuals with low vitamin D status had more days with upper respiratory tract illness symptoms during four months of winter training than athletes who had adequate or optimal vitamin D status.
Athletes performing prolonged intensive exercise, or with heavy schedules of training and competition, catch more colds because the associated physical and mental stress affects their immune system.
For the study, athletes were classed into four groups (optimal, adequate, inadequate, or deficient) according to their vitamin D status, based on a blood test measuring the concentration of 25-hydroxy vitamin D. Participants completed a daily questionnaire on respiratory illness symptoms, and blood and saliva samples were collected before and after the four-month study period to assess their vitamin D status and immune function.
At the start of the study 38% of athletes had either deficient or inadequate vitamin D status and by the end of the study this has increased to 55%. The average number of cold episodes was three times higher in the deficient group compared with the optimal group.
Furthermore, those who were deficient in vitamin D had longer lasting colds and their illness symptoms were more severe.
Low vitamin D status was associated with lower levels of salivary immunoglobulin A (IgA) and white blood cell cytokine production. Salivary IgA is important in preventing viral infections – particularly in the respiratory tract – and cytokines are important in activating immune defences when infections begin.
Project lead Professor Michael Gleeson said:
“It seems that many athletes, even those training mostly outdoors, do not get enough sunlight in the winter months in the UK to maintain normal vitamin D status and that this increases their risk of picking up respiratory infections.
“Athletes hate the thought of picking up colds as even minor ailments can impair their training and performance or even stop them from competing.”
Michael Gleeson is Professor of Exercise Biochemistry in Loughborough University’s School of Sport, Exercise and Health Sciences.
The research was published this month in Exercise Immunology Review.
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Notes for editors:
The paper Influence of vitamin D status on respiratory infection incidence and immune function during 4 months of winter training in endurance sport athletes, Cheng-Shiun He, C.-H., Handzlik, M., Fraser, W.D., Muhamad, A., Preston, H., Richardson, A. and Gleeson, M. (2013) is published in Exercise Immunology Review 19: 86-101.
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