Trend changes in age-related body mass index gain after coronavirus disease 2019 pandemic in Japan: a multicenter retrospective cohort study

BACKGROUND: Accumulating studies suggest that strict lockdown with enforcement including segregation to control the coronavirus disease 2019 (COVID-19) pandemic is associated with excess weight gain, but the such lockdown was not practiced in Japan. We aimed to compare the age-related weight gain before and after the COVID-19 pandemic in Japan where achieved epidemic control based on individual voluntary action. METHODS: This multicenter retrospective cohort study used electronic data from annual health checkups for workers from January 2015 to December 2021 at four facilities belonging to the Central Clinic Group, Aichi, Japan. We defined pre-pandemic and post-pandemic periods as January 2015–December 2019 and January 2020–December 2021, respectively. Participants were grouped by sex, age, and body mass index (BMI) stratus as of 2015, and the pre-pandemic and post-pandemic age-related BMI changes in overall individuals and each specific group were compared using a paired t-test. RESULTS: The total number of eligible participants was 19,290. During the pre-pandemic period, the mean BMI increased linearly in every group. The mean age-related BMI changes in females’ pre-pandemic and post-pandemic periods were + 0.11 and + 0.02 kg/m(2)/year, respectively. This significant decrease was also shown in males, + 0.11 in the pre-pandemic and − 0.02 kg/m(2)/year in the post-pandemic periods. The reduction was consistently observed in all age strata. Furthermore, a significant reduction was also observed in the normal-weight females of reproductive ages aged 15–44 years. CONCLUSIONS: This is the first report showing that age-related weight gain was reduced after the COVID-19 pandemic in Japan, which could affect the reproductive age of females. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12958-023-01061-1.