After 12 months , there were significant differences in the serum 25 ( OH ) D concentration ( mean difference : 49.54 ; 95 % CI : 43.94 to 55.14 ) nmol/l ) and PTH levels ( mean difference : -1.02 ; 95 % CI : -1.67 to -0.38 pmol/l ) in the intervention group compared to placebo group .