Unhappy or anxious? How you sleep may be the cause

(CNN) — Not getting enough sleep or sleeping poorly can greatly affect your mood and mental health, according to a new study analyzing 50 years of research.

“We found that all forms of sleep loss — total sleep deprivation, partial sleep loss, and sleep fragmentation — resulted in emotional changes. The strongest and most consistent effect was that sleep loss reduced positive mood,” said co-lead author Cara Palmer, assistant professor and director of the Sleep and Development Lab at Montana State University in Bozeman.

“We also found that sleep loss increased feelings of anxiety,” Palmer said in an email. “When experiencing emotional events, people were also more likely to report reacting differently than people who were well-rested.

“Specifically, they reported feeling less emotional arousal, which is when we feel the intensity of certain emotions in our body, suggesting that overall people felt more muted emotional responses after sleep loss.”

Adults over 18 need at least seven hours of solid sleep at night to be healthy, according to the US Centers for Disease Control and Prevention. When they fall short of that minimum, the toll can be steep: Studies have linked poor sleep to an increased risk of obesity, heart disease and dementia, as well as mood disorders.

Despite the risks, more than 30% of adults have a daily sleep debt — when you sleep less than your body needs — of over an hour, while nearly 1 in 10 adults are missing two or more hours of sleep each night, a 2022 study found.

“Across the world, individuals rarely get the recommended amount of sleep for at least 5 nights per week,” said study co-lead Jo Bower, a lecturer at the University of East Anglia in Norwich, England, in an email. “Our work shows the potential consequences of this for our emotional health, at a time where mental health problems are rising rapidly.”

Types of sleep loss

Published Thursday in the American Psychological Association’s journal Psychological Bulletin, the research analyzed data from 154 studies on more than 5,000 people across five decades.

In those studies, researchers disrupted the sleep of participants for one or more nights, either by keeping them awake (sleep deprivation), waking them periodically (sleep fragmentation) or making them get up earlier than usual (partial sleep loss). Afterward, participants were tested for anxiety, depression, mood and their response to emotional triggers.

“Generally, total sleep deprivation had a larger impact on mood and emotions compared to partial sleep loss or fragmented sleep,” Palmer said. “Interestingly though, the effect of sleep on positive mood occurred even after short periods of sleep loss, like staying up an hour or two later than usual or after losing just a few hours of sleep.”

The “large and comprehensive” metanalysis emphasizes the strong connections between mental health and sleep, said sleep specialist and pulmonologist Dr. Raj Dasgupta, an associate professor of clinical medicine at the University of Southern California’s Keck School of Medicine. He was not involved in the research.

“Maybe there is truth behind the saying: ‘woke up on the wrong side of the bed,’” Dasgupta said in an email. “Studies included in the meta-analysis found that subjects who (had) poor quantity and quality sleep reported feeling more stressed, angry, sad, and mentally exhausted. When the subjects resumed normal sleep, they reported a dramatic improvement in mood.”

What’s going on?

What is it about sleep that makes our body behave this way? The answers lie in the brain, Palmer said.

“We know from prior research that sleep loss impacts the neural circuitry involved in experiencing reward or positive experiences, which likely plays a role,” she said. “We also see heightened reactions in areas of the brain that are involved in the experiences of emotion. …

“At the same time, connections between our emotion centers of the brain and our prefrontal cortex, which helps us appropriately control our emotional reactions, are impaired.”

While all types of sleep impairment affected mood, the study found reactions to emotional experiences were more negative after loss of rapid eye movement (REM) sleep when compared with losing slow-wave or “deep” sleep.

During slow-wave sleep, the body removes potentially harmful materials from the brain — including beta-amyloid protein, a hallmark sign of Alzheimer’s disease — while REM is the stage of sleep in which we dream and information and experiences are consolidated and stored in memory.

“It is likely that both are important, but in different ways,” Bower said. “For example, previous work has shown that REM sleep may be linked to processing of emotional memories and so could have an effect on mood through cognitive processes.”

Slow-wave sleep, however, may be linked to reward centers of the brain, which could influence responses to positive emotional situations, she said.

Deep sleep is considered one of the best markers of sleep quality, because a person must typically have relatively uninterrupted sleep to achieve it. Since each sleep cycle is roughly 90 minutes long, most adults need seven to eight hours of relatively uninterrupted slumber to achieve restorative sleep, according to the CDC.

Impact on anxiety and depression

Loss of sleep also worsened symptoms of anxiety and depression, according to the study, even in people without known psychiatric or physical health conditions.

“Longer periods of wakefulness resulted in more extreme depressive or anxiety symptoms,” Palmer said. “It is likely that sleep loss may affect people who are already depressed or who have a genetic risk for depression differently. For example, some of our prior work suggests that individuals who (are) already anxious may experience exaggerated responses to sleep loss.”

Difficulty sleeping may also be one of the first signs of an emerging mental disorder, Dasgupta said.

“Chronic insomnia may increase an individual’s risk of developing a mood disorder, such as depression or anxiety,” he said. “Lack of sleep can be an even greater risk factor for anxiety. Studies included in the meta-analysis show that individuals with insomnia were more likely to develop an anxiety disorder and that insomnia is also a reliable predictor of depression.”

Obstructive sleep apnea, in which the body can stop breathing for 10 seconds or more at a time, can also create fragmented and disturbed sleep, Dasgupta said. This type of sleep disorder “occurs more frequently in people with psychiatric conditions and needs to be addressed,” he said.

More research is needed to determine the impact of poor sleep on people with existing mental disorders, teens and children, but each person should be careful to prioritize sleep in their lives, Bower said.

“Allowing yourself time to sleep is an important act of self-care, much like eating well and taking exercise, Bower said. “It is also important that we make systemic changes that support the ability of individuals to get good-quality sleep.

“This includes considering policies relating to school start times, working hours, shift patterns, and access to health care which supports treatment of sleep problems.”

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