Researchers at Tel Aviv University tracked 58 young adults in two groups: those who got four hours of sleep and those who got eight but had that sleep repeatedly interrupted by tasks of at least 10 minutes — not unlike waking to feed or soothe an infant, or dealing with work during an on-call shift.

Such interruptions “disrupt the natural sleep rhythm. The impact of such night wakings on an individual’s daytime alertness, mood and cognitive abilities had never been studied,” Avi Sadeh, a professor at the university’s School of Psychological Sciences said in a statement. Sadeh directs a sleep clinic at the university. “Our study demonstrates that induced night wakings, in otherwise normal individuals, clearly lead to compromised attention and negative mood.”

“Vast proportions of the population experience night wakings regularly due to occupational demands, environmental circumstances or the very common parental need to tend to a child during the night,” the researchers wrote recently in the journal Sleep Medicine. They cited a study of nearly 30,000 parents in 11 countries that showed about a quarter wake up twice a night with their children up to age 3, and an additional 19.5% reported an average of three or more night wakenings.