Daily stress predicts nighttime wakefulness through cognitive arousal

A new study reveals that daily stress is associated with racing thoughts at bedtime, which in turn predicts disrupted sleep for nearly everyone. However, people who are naturally prone to stress-induced sleep loss experience higher overall stress and prolonged nighttime wakefulness compared to more resilient sleepers. The findings were published in the Journal of Sleep Research.

Chronic stress is a well-documented risk factor for a host of physical and mental health issues. One common way stress harms the body is by disrupting rest. Many people experience heightened cognitive activity, like worry or rumination, right before bed. Others experience physical symptoms like an elevated heart rate or sweating. Both types of arousal can interfere with the body’s ability to transition into restful sleep.

Not everyone reacts to daily pressures the same way. Some individuals possess high sleep reactivity, meaning they are particularly vulnerable to losing sleep when faced with stressful situations. Sleep researchers often frame this using a three-part model. Sleep reactivity acts as a predisposing vulnerability. Daily stressors act as precipitating events. Finally, pre-sleep arousal acts as a perpetuating mechanism that keeps the cycle going.

Prior research into this vulnerability often relied on broad annual surveys or focused on major life events, like job loss or bereavement. While these major events are impactful, they are relatively infrequent. Everyday pressures, such as academic deadlines or interpersonal arguments, accumulate over time and affect health.

Researchers wanted to understand exactly how routine stress, pre-sleep arousal, and baseline sleep reactivity interact on a daily basis. The research team was led by Noof Abdullah Saad Shaif, Stijn A. A. Massar, and Ju Lynn Ong at the National University of Singapore. They designed a study to track both the mental and physical aspects of nighttime arousal simultaneously, filling a gap in a field that often studies these factors in isolation.

The researchers recruited full-time university students who did not have existing sleep disorders or psychiatric conditions. They administered a standard questionnaire to measure sleep reactivity in 264 eligible participants. From this pool, the researchers selected 30 students with the highest vulnerability to stress-induced sleep loss and 30 students with the lowest vulnerability.

This group of 60 students participated in a two-week monitoring period during their regular academic semester. The researchers instructed the participants to wear wrist actigraphy monitors. These devices use motion sensors to objectively record sleep patterns in a natural environment. The monitors logged when a person fell asleep, how much total sleep they achieved, and how many minutes they spent awake in the middle of the night.

Participants also wore a smart ring that recorded their heart rate in the 20 minutes before bedtime. This provided an objective measure of physical arousal that could be compared against self-reported physical symptoms. Each night before bed, the students completed a survey rating their perceived stress levels for that day. The following morning, they filled out another survey to report how much cognitive and physical arousal they remembered experiencing the night before.

The team collected 800 nights of matched survey and tracker data. They analyzed the results in two distinct ways to capture both short-term fluctuations and long-term group differences.

First, they looked at day-to-day fluctuations within each individual. They found that on days when a student reported higher stress than their own personal average, they experienced more racing thoughts at bedtime. This cognitive arousal predicted less total sleep time and a longer wait to fall asleep. This pattern occurred consistently across the board, regardless of whether the student had high or low baseline sleep reactivity.

Next, the researchers analyzed the differences between the two groups. In this comparison, baseline sleep reactivity played a substantial role. Students in the high sleep reactivity group reported greater average stress and higher cognitive arousal over the two weeks. They did not actually experience a higher number of stressors than the low-reactivity group. Instead, their perception of the stress was amplified.

This heightened mental arousal predicted longer periods of wakefulness in the middle of the night for the highly reactive group compared to the low-reactive group. The researchers suggest that racing thoughts at bedtime might carry over into the night. When highly reactive individuals experience normal nighttime awakenings, intrusive thoughts may resurface, making it harder to fall back asleep.

The physical measurements yielded an unexpected result. Neither self-reported physical symptoms nor the objective heart rate data mediated the relationship between daily stress and sleep disruption. The differences in objective heart rate between the high and low reactivity groups were not statistically significant.

In this sample, cognitive arousal was the primary mechanism connecting daytime stress to nighttime wakefulness. The researchers noted that minor daily stressors might not be severe enough to trigger pronounced physical responses, such as a spiking heart rate.

The study relies on a specific demographic, consisting mainly of young, female, Chinese university students in Singapore. These results might not apply to older adults, different cultural groups, or clinical populations with diagnosed sleep disorders. The types of stress experienced by university students may also differ from the chronic pressures faced by other groups.

The timing of the surveys presents another limitation. Participants reported their pre-sleep arousal the morning after it occurred, rather than in the moment. The researchers chose this design to avoid introducing artificial stress or screen light right at bedtime, which could contaminate the sleep tracking data. This means the self-reported mental arousal was retrospective. The responses could have been influenced by how well the participant felt they slept that night.

Future research could investigate whether interventions like cognitive behavioral therapy for insomnia can help retrain the brain to handle stress better. By targeting racing thoughts and rumination, people with high sleep reactivity might learn to protect their rest against the wear and tear of daily life. Tracking these metrics in a wider variety of people could also reveal if physical arousal plays a larger role in groups facing more severe types of trauma.

The study, “Sleep Reactivity Amplifies the Impact of Pre-Sleep Cognitive Arousal on Sleep Disturbances,” was authored by Noof Abdullah Saad Shaif, Julian Lim, Anthony N. Reffi, Michael W. L. Chee, Stijn A. A. Massar, and Ju Lynn Ong.