Habitual moderate alcohol consumption desynchronizes circadian physiologic rhythms and affects reaction-time performance.

The authors studied longitudinally four healthy young adults to explore if habitual evening intake of a "moderate" amount of wine alters parameters, including period (τ) of circadian rhythms. Subjects, synchronized by diurnal activity from 07.30 h ± 60 min to 23.00 h ± 90 min and nocturnal rest, were studied during a continuous 22-day span: 11 days without alcohol (control) and 11 days with a glass (200 mL) of wine nightly at supper (alcohol). The amount of alcohol ingested with dinner ranged from 0.28 to 0.42 g/kg/24 h/participant and the estimated evening blood alcohol level ranged from 0.02 to 0.10 g/L/participant. Single reaction time (SRT; yellow light signal), three-choice reaction time (CRT) (red, green, and yellow signals) of both hands, related cumulated errors (c-errors), as well as oral temperature (OT) and grip strength (GS) were measured four to seven times/24 h. Time series were analyzed individually to quantify 24-h means (M), circadian τ (power spectra), and cosinor, and correlation, χ(2), and t tests were performed. The sleep-wake τ (actography) was 24 h in every subject for both conditions. With alcohol, all subjects showed an OT circadian τ shorter than the control one. The SRT circadian M was longer (poorer performance) with wine versus control in three subjects, while CRT was longer with wine versus control in only one subject. Correlation analyses also showed the detrimental effect of alcohol on the same variables. Number of days with <2 c-errors was predominant in control and decreased with alcohol, especially for SRT. The desynchronization of the 10 different documented rhythms was greater with alcohol with reference to control in two of the four studied subjects. This work shows that habitual "moderate" wine drinking at supper reduces the performance of subjects, increases the level of c-errors/24 h, especially for SRT, suggesting a "moderate" amount of alcohol has the potential to increase accident risk, and it can also desynchronize circadian time organization.