Abstract

Andrew P. Smith*

ABSTRACT

Background: Research has demonstrated that psychosocial factors, such as stress, and health-related behaviors, such as smoking, are associated with an increased risk of upper respiratory tract illness (URTI). A recent review has suggested that these results can be interpreted within a fatigue framework. Caffeine can act as a countermeasure to fatigue which suggests that it may be associated with a reduced incidence of URTIs. Methods: These issues were examined here by carrying out a secondary analysis of data from a representative UK sample (N=6418). Fatigue was measured by being tired for no apparent reason. An URTI factor measuring cold/influenza and the symptoms of blocked/runny nose, sore throat and cough was the dependent variable. Caffeine consumption was measured from the number of caffeinated beverages consumed. Established predictors of URTIS (e.g. age and smoking) were also used in the analyses. Results: Initial cross-tabulations showed that fatigued individuals and non-caffeine consumers were more likely to be in the high URTI category. Combining fatigue and caffeine showed that the effect of caffeine was to reduce the association between fatigue and URTIs. Logistic regression showed that the effects of fatigue and caffeine remained significant when possible confounders were statistically controlled. Established predictors such as age and smoking showed an association with URTIs, which gives more confidence in the novel findings. Conclusions: There are plausible biological mechanisms linking fatigue and susceptibility to URTIs and caffeine and fatigue, which provides a strong theoretical framework for the new interpretation of established findings. The new empirical results presented here provide the first support for this model.