Betel nut chewing is a popular habit in Taiwan, and it is associated with adverse metabolic effects. The aim of this study was to investigate correlations between betel nut chewing with metabolic syndrome (MetS) and its components in a longitudinal study using data from the Taiwan Biobank. A total of 121,423 participants were included in the baseline study, and 27,002 received follow-up examinations after a median of 4 years. The association between betel nut chewing and MetS was analyzed using multiple logistic regression after controlling for confounders. The baseline prevalence of MetS was 22.5%. Multivariable analysis showed that a history of chewing betel nut was significantly associated with baseline MetS (odds ratio (OR) = 1.629; 95%...