There were no significant differences between groups in physical activity ( difference : +1.50 kJ kg ( -1 ) day ( -1 ) ; 95 % CI -1.74 , 4.74 ) , plasma vitamin C ( difference : -3.84 mol/l ; 95 % CI -8.07 , 0.38 ) , smoking ( OR 1.37 ; 95 % CI 0.77 , 2.43 ) and plasma drug levels ( difference in metformin levels : -119.5 mol/l ; 95 % CI -335.0 , 95.9 ) .