The Effect of Doogh (Yogurt Drink) on Reaction Time and Vigilance- Sleepiness of Healthy Young Adults

Doogh is a traditional dairy product, which is widely used as a popular drink in the Middle East, in general, and in Iran, in particular. There has been no research study regarding its effects on vigilance and mental-cognitive performance so far; the present study aimed at investigating this effect.
The current study aimed at objectively evaluating the effect of Doogh (Yogurt drink) on attention, reaction time and vigilance- sleepiness of healthy young adults.
In this repeated measurement study, participants included 17 healthy adults between 20 and 40 years old, with adequate night sleep and without any symptoms of daytime sleepiness that entered the clinical trial one at a time via public invitations. The intervention included drinking 250 cc of doogh or water in the morning or in the afternoon. Therefore, there were 4 interventions for each participant with random sequences, lasting 3 to 5 days. Right before and 1.5 to 2 hours after drinking each of the drinks, the participants were assessed using test of variables of attention (TOVA) and sleepiness test via the visual analogue scale (VAS). The data were analyzed by paired t test and Generalized Estimating Equation (GEE) model at the final stage.
Ten female and 7 male participants took part in the study. Doogh caused a significant increase in reaction time and commission error and reduced vigilance. These changes occurring after drinking doogh were significant in the afternoons, while they were insignificant in the mornings despite the fact that they lasted longer. There was no change regarding TOVA variables caused by water in any of the case. Although reduced level of vigilance was observed after drinking water, the differences were more significant with regards to doogh and its post intervention comparison with water was meaningful.
Doogh caused sleepiness in the afternoon time along with a significant increase in reaction time and commission and omission errors. Regarding the cognitive effects of doogh, the timing and activity type of the drinker should be taken into account. Positive effects of drinking doogh on sleepiness and the risk of accidents caused by drinking it should be studied in other research projects.