Purpose: Upper respiratory tract infection (URTI) is the most common reason for seeking primary care in many countries. Still, little is known about potential strategies to reduce susceptibility. We investigated the relationships between physical activity level, perceived stress, and incidence of self-reported URTI.
Methods: We conducted a population-based prospective cohort study of 1509 Swedish men and women aged 20-60 yr with a follow-up period of 4 months. We used a Web-based questionnaire to assess disease status and lifestyle factors at the start of the study. We assessed physical activity and inactivity as total MET-hours (MET task) per day and perceived stress by the 14-item Perceived Stress Scale. Participants were contacted every 3 wk via e-mail to assess incidence of URTI. They reported a total of 1181 occurrences of URTI. We used Poisson regression models to control for age, sex, and other potential confounding factors.
Results: We found that high levels of physical activity (≥55 MET·h·d−1) were associated with an 18% reduced risk (incidence rate ratio (IRR) = 0.82, 95% confidence interval (CI) = 0.69-0.98) of self-reporting URTI compared with low levels of physical activity (<45 MET·h·d−1). This association was stronger among those reporting high levels of stress (IRR = 0.58, 95% CI = 0.43-0.78), especially among men (IRR = 0.37, 95% CI = 0.24-0.59), but absent in the group with low levels of stress.
Conclusions: We found that high physical activity was associated with a lower risk of contracting URTI for both men and women. In addition, we found that highly stressed people, particularly men, appear to benefit more from physical activity than those with lower stress levels.
1Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, SWEDEN; 2Osher Center for Integrative Medicine, Karolinska Institutet, Stockholm, SWEDEN; 3Department of Medicine, Clinical Epidemiology Unit, Karolinska Institutet, Stockholm, SWEDEN; 4Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, SWEDEN; 5Department of Clinical Neuroscience, Karolinska University Hospital, Stockholm, SWEDEN; 6Stress Research Institute, Stockholm University, Stockholm, SWEDEN; 7School of Computer Science and Communication, Royal Institute of Technology, Stockholm, SWEDEN; 8RTI Health Solutions, Research Triangle Park, NC; and 9Departments of Epidemiology and Medicine, Boston University School of Public Health, Boston, MA
Address for correspondence: Elinor Fondell, Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Nobels vag 12a, 171 77 Stockholm, Sweden; E-mail: Elinor.Fondell@ki.se.
Submitted for publication March 2010.
Accepted for publication June 2010.