When parents of infant children talk about their lives, you’ll hear words like “exhausting” or “hellish” nearly as often as “miraculous” and “life changing.” New parents have notoriously disturbed sleep. Whether the crying is for a feeding, a diaper change or nothing at all, the result is always the same: fragmented sleep.

The price of multiple night waking is the same as staying up nearly the entire night. Scientifically speaking, the negative cognitive impact, shortened attention span and poor moods are equivalent to no more than four consecutive hours of sleep.

It’s hard to blame them for having mixed feelings about parenting.  They often wake up in the morning feeling more tired than the night before.

Doctors or other professionals who are on call experience the same physiological phenomenon. It takes only a short phone call to fully interrupt a sleep cycle.

“These night wakings could be relatively short – only five to ten minutes – but they disrupt the natural sleep rhythm,” said Avi Sadeh, PhD, the lead author of the Tel Aviv University study. “Night wakings, in otherwise normal individuals, clearly lead to compromised attention and negative mood.”

The study monitored the alertness and attention of college students awoken by a series of overnight phone calls. The students wore wrist actigraphs to track when they slept. Following the baseline eight-hour night of uninterrupted sleep, the students were subjected to equivalent of an on-call night. A phone call woke the subjects up a total of four times. Each time the phone rang, they had to complete a short task on a computer and go back to sleep.

The following morning the students had to complete several computer-based tests and fill out questionnaires. All it took was a single night of interruptions to result in a measurably compromised attention and bad mood.

For most people, the solution to this problem is simple: keep the phone out of the bedroom and run some white noise if the environment is noisy. Parents and on-call professional are unfortunately out of luck. So next time your friend who is a new parent complains, have a little sympathy.