The goal of this study was to investigate the effects of smoking and tea consumption on urinary fluoride ion (F) levels and whether any interactive effects occurred. Three hundred university students were recruited to provide urinary samples. An Orion 4-Star ion-meter, equipped with an ion selective electrode (ISE), was used for the measurements of the F levels in the urine samples. Initially, the urinary F values studied in the smoking and tea consumption groups were evaluated by t-test and ANOVA. After this stage, the relationship between smoking and tea consumption groups was analyzed by correlation, regression, and two-way ANOVA tests. A significant difference (p<0.01) was found in the urinary F data between the smoking and nonsmoking groups. Significant differences (p<0.001) were also found among the tea beverage consumption groups. Significant positive correlations were present between the urinary F levels and both smoking and the quantity of tea consumption (r=0.170, p=0.003, and r=0.424, p<0.001, respectively). A significant relationship was observed between smoking and the quantity of tea consumption in their effect on the urinary F levels by means of regression analysis (r2=19.4%, p<0.001) and two-way ANOVA tests
(F=2.15, p<0.05). Consequently, it appeared that the urinary F levels can be increased by
smoking and tea consumption both together and separately and that there is an interaction between smoking and tea consumption in their effect on urinary F levels.