Sleep restriction was associated with significant impairment in FMD ( 8.64.6 % during the initial pre-randomization acclimation phase versus 5.23.4 % during the randomized experimental phase , P = 0.01 ) whereas no change was seen in the control group ( 5.03.0 during the acclimation phase versus 6.732.9 % during the experimental phase , P = 0.10 ) for a between-groups difference of -4.40 % ( 95 % CI -7.00 to -1.81 % , P = 0.003 ) .