Cold water swimming and upper respiratory tract infections

It is often suggested that habitual cold water swimming (HCS) may improve resistance to infection [1], yet research into effects of HCS on the immune system has produced inconclusive results. This may be due to the wide range of protocols, from brief ice-cold dips [2] to long cold water swims [3]. Many studies measured blood and saliva markers rather than actual illness, and the clinical significance of these markers is not well established [4]. Incidence of upper respiratory tract infection (URTI), i.e. the common cold, is a useful indication of in vivo immune system function [5,6]. This study compared URTI susceptibility in those practising HCS with that in their non-swimming co-habiting partners. To control for any effect of swimming, those who swim in indoor heated pools and their partners were also investigated. The null hypothesis (H0) was that there would be no difference between swimming groups.