The adjusted odds ratios for IGT for rock tea consumption of < 1 , 1-15 , 16-30 , and > 30 cups per week were 1.0 ( reference ) , 0.69 ( 95 % CI , 0.48-0 .98 ) , 0.59 ( 95 % CI , 0.39-0 .90 ) , and 0.64 ( 95 % CI , 0.43-0 .97 ) , respectively .