Supplementary Material for: Nine-year trend in the prevalence of allergic diseases and their associated factors in young adults

Introduction: Notably, few studies have evaluated the recent changes in the prevalence of allergic diseases in young adults. Studies examining the risk of allergy in two populations with similar social backgrounds, other than the region in which they live, are rare. Methods: First-year students from Hokkaido University were enrolled in this study between 2011 and 2019. A questionnaire survey was conducted to determine the annual prevalence of current wheeze, seasonal allergic rhinitis (SAR), and perennial allergic rhinitis (PAR) in non-smoking young adults. Trends in the presence of these disease conditions were evaluated based on their hometowns (Hokkaido and outside Hokkaido separately) due to the low prevalence of cedar pollen allergies in Hokkaido. The association between these disease conditions and body mass index (BMI) was also assessed. Results: The prevalence of current wheeze and PAR food allergies did not change in both regions. SAR showed a significantly increasing trend; however, the prevalence of SAR was higher among those whose place of origin was not Hokkaido. Current wheeze was positively associated with obesity (P < 0.05), whereas the high prevalence of SAR was not associated with body weight. In contrast, a lean body type was significantly associated with a higher prevalence of PAR (P < 0.05). Discussion/Conclusion: The prevalence of current wheeze was stable, and that of PAR has decreased over the past nine years. However, the prevalence of SAR in Hokkaido has been increasing in Japanese young adults. A differential association between current wheeze and BMI was observed when comparing PAR and SAR.