Most of the rockets fired at Israel from Gaza by Palestinian militants cause little physical damage, but they cause a great deal of psychological harm. A new study shows that repeated late-night warning sirens and trips to the bomb shelter can extract their price in the morning.

Tel Aviv University researchers examined the effects of interrupted sleep in the first study of its kind, conducted before the latest conflict between Israel and Gaza militants. They found that being jolted awake several times a night may be as physically detrimental as getting no sleep at all. The study, according to lead researcher Prof. Avi Sadeh of Tel Aviv University’s School of Psychological Sciences, “demonstrates that induced night wakings, in otherwise normal individuals, clearly lead to compromised attention and negative mood.”

As missiles rain down on Israeli cities, Code Red missile alert sirens are likely to go off at any time, including during the late-night hours — interrupting the slumber of even those who are already sleeping in protected rooms and bomb shelters, as many in southern Israel have been doing in recent weeks. That, according to Sadeh, is far worse for health than previously suspected. “Sleep research has focused in the last 50 years on sleep deprivation, and practically ignored the impact of night-wakings, which is a pervasive phenomenon for people from many walks of life,” said Sadeh.

“The impact of such night wakings on an individual’s daytime alertness, mood, and cognitive abilities had never been studied,” said Sadeh, who has for years worked with children and adults with sleep disorders and has written a book on the subject. “Many previous studies had shown an association, but none had established a causal link. Our study is the first to demonstrate seriously deleterious cognitive and emotional effects.” The study appears in the latest edition of the journal Sleep Medicine.

Residents of communities in the line of rocket fire are far from the only victims of interrupted sleep. You don’t need a national emergency to be roused from your slumber, said Sadeh. “The sleep of many parents is often disrupted by external sources, such as a crying baby demanding care during the night. Doctors on call, who may receive several phone calls a night, also experience disruptions.” It doesn’t take much of an interruption, added Sadeh. “These night wakings could be relatively short — only five to 10 minutes — but they disrupt the natural sleep rhythm.”

That’s enough to put victims in a really bad mood, the study shows. Student volunteers at TAU’s School of Psychological Sciences had their sleep patterns monitored at home using an actigraph, a wristwatch-like device that detected when they were asleep and when they were awake. The 13 students, chosen for their consistent sleep patterns, were allowed to sleep a normal eight-hour night on the first night, but on the second night they were subjected to various interruptions — awakened four times by phone calls and told to complete a short computer task before going back to sleep after 10-15 minutes of wakefulness.

The next morning, the students were assessed using questionnaires and computer-related tasks for how alert and attentive they were and what their mood was. The results surprised even Sadeh and his team, which included TAU researchers Michal Kahn, Shimrit Fridenson, Reut Lerer and Yair Ben-Haim. After just one night of frequent interruptions, the students’ ability to concentrate was significantly compromised, showing “performance significantly poorer following the night of initiated sleep disturbance compared to the normal sleep night,” the study said.

They were in a very bad mood, too. “Following a night of sleep restriction or prolonged awakenings, the participants reported significantly higher depression, fatigue and confusion levels and reduced vigor compared to their reports of mood following their control sleep night,” the study said, adding that “fragmented sleep thus could be more, less or equally damaging in comparison to sleep restriction, depending on the extent of disruption.”

As this is the first time this kind of study has been conducted, Sadeh regards it as a pilot. Further research is needed, according to the study’s authors, to explore the differences between “spontaneous” (where a sleeper awakens on their own) and “induced” (where they are nudged out of sleep) awakenings, the effects of behavioral demands on the awakened sleeper, as when a parent needs to deal with a crying infant, and whether some extra sleep can compensate for the loss of shut-eye the night before.

Nevertheless, the study is significant for its introduction of the issue to scientific evaluation. “Our study shows the impact of only one disrupted night,” said Sadeh. “But we know that these effects accumulate, and therefore the functional price new parents — who awaken three to 10 times a night for months on end — pay for common infant sleep disturbance is enormous. Besides the physical effects of interrupted sleep, parents often develop feelings of anger toward their infants and then feel guilty about these negative feelings,” he said.

“Sleep research has focused in the last 50 years on sleep deprivation and practically ignored the impact of night-wakings, which is a pervasive phenomenon for people from many walks of life,” Sadeh noted. “I hope that our study will bring this to the attention of scientists and clinicians, who should recognize the price paid by individuals who have to endure frequent night-wakings.”

Though it’s probably little comfort to millions of Israelis waking up several times a night to the disruptive and sometimes frightening wail of air raid sirens — at least they know now that if they feel groggy and cranky in the morning, they’re not alone.