Demographic and lifestyle characteristics and selected NPC risk factors of the study population in Guangzhou, China

1 Continuous variables were shown as the means±standard deviation. Categorical variables were shown as numbers (percents). Variables were evaluated in conditional logistic model.2 Variables were scored as yes or no, and numbers (percents) of yes responses were listed. House decoration refers to replacement of floor board, wall, and indoor painting for almost a whole flat or house; new furniture refers to a set of new furniture for living room(s) and bed room(s). 3 Occupation was categorized into 3 levels on the basis of the intensity of occupational physical activity.4 Smoking status was defined as current smoker, ex-smoker or nonsmoker (a smoker was defined as someone smoking at least one cigarette per day for at least six months).5 Passive smoking was designated as exposure to other peoples' tobacco smoke for at least 5 minutes daily in the previous five years.6 Physical activity was defined as occupational, leisure time and household chores activity, and evaluated by metabolic equivalent hours per day (MET∙ h/d).Abbreviations: BMI: body mass index; NPC: Nasopharyngeal carcinoma; MET: metabolic equivalent1 .