Obesity and risk of respiratory tract infections: results of an infection-diary based cohort study

BACKGROUND: Respiratory tract infections (RTIs) are a major morbidity factor contributing largely to health care costs and individual quality of life. The aim of the study was to test whether obesity (BMI ≥ 30 kg/m(2)) is one of the risk factors underlying frequent RTIs in the German adult population. METHODS: We recruited 1455 individuals between 18 to 70 years from a cross-sectional survey on airway infections in Germany and invited them to self-report in diaries incident RTIs experienced during three consecutive winter/spring seasons. RTIs reported in these 18 months and summary measures adding-up individual RTIs were the outcomes of interest. RESULTS: Compared to individuals with normal weight, obese individuals reported a consistently higher frequency of upper and lower RTIs and predominantly fell in the upper 10% group of a diary sumscore adding-up 10 different RTI symptoms over time. Obesity was associated both with lower RTIs ((adjusted)OR = 2.02, 95%CI = 1.36–3.00) and upper RTIs ((adjusted)OR = 1.55, 95%CI = 1.22–1.96). Adjusting for demographic and lifestyle variables did only marginally affect ORs. Stratified analyses suggested a stronger association for women and effect modifications by sports activity and dietary habits. CONCLUSIONS: We confirm the association of obesity with infection burden and present evidence for putative interaction with sports activity and dietary patterns. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12889-018-5172-8) contains supplementary material, which is available to authorized users.