There were no significant differences in primary outcomes between the caffeine group and the placebo ( adjusted mean difference of -6.7 [ 95 % confidence interval ( CI ) = -15.3 to 2.0 min ] ; P = 0.13 for actigraphic total sleep time ; and adjusted rate ratio [ caffeine/placebo ] for apnea-hypopnea index of 0.89 [ 95 % CI = 0.55-1 .43 ] ; P = 0.63 ) .