In a recent study conducted by researchers at Stockholm University and published in the Proceedings of the Royal Society B, an intriguing connection between sleep and subjective age was found. The study’s findings suggest that the quantity of sleep we get can significantly influence our perception of age, making us feel either years younger or older than our actual age.
Prior research has suggested that feeling younger than our calendar age might be beneficial for brain health, with older adults who feel younger showcasing a younger predicted brain age and larger volumes of grey matter in several brain regions. Moreover, feeling younger is linked to a longer lifespan, better mental and physical health, and more positive psychological traits such as optimism and resilience.
Noting sleep’s role in overall well-being and cognitive function, the researchers sought to uncover whether sleep patterns could be a contributing factor to feeling younger.
“Given that sleep is essential for brain function and overall well-being, we decided to test whether sleep holds any secrets to preserving a youthful sense of age,” said study author Leonie Balter, a psychoneuroimmunologist and researcher at the Department of Psychology at Stockholm University.
The research comprised two distinct studies: a cross-sectional analysis and an experimental sleep restriction study.
The first study included 429 participants who were fluent in English and residing in the United Kingdom. Participants completed a survey through their mobile smartphones during a fixed time window in the afternoon, ensuring that the assessment of subjective age and sleepiness was consistent across respondents. The key measure of interest, subjective age, was captured using a single-item question asking participants to reflect on how old they felt at that moment, with responses anchored between 12 and 120 years.
The researchers found that both increased sleepiness and a greater number of days with insufficient sleep over the last 30 days were associated with feeling older than one’s calendar age. Specifically, each additional day of perceived insufficient sleep was correlated with feeling 0.23 years older, while each unit increase in sleepiness on the Karolinska Sleepiness Scale (KSS) was associated with feeling 1.22 years older. Notably, participants who reported no days of insufficient sleep felt significantly younger than their calendar age.
The second study involved a randomized crossover design with 186 participants, ranging in age from 18 to 46 years. The study aimed to directly assess how two distinct sleep conditions — sleep saturation and sleep restriction — affect how old participants feel relative to their actual age.
Sleep saturation involved two days with nine hours in bed each night, simulating an ideal sleep duration, whereas sleep restriction entailed two days with only four hours in bed per night, mimicking acute sleep deprivation.
Participants adhered to their assigned sleep schedules in their own homes, maintaining a sleep diary and wearing an actigraph to monitor sleep patterns and physical activity for seven days leading up to laboratory visits. The last two nights of this period were dedicated to the sleep condition (either sleep saturation or sleep restriction).
Participants felt significantly older — by an average of 4.44 years — after experiencing sleep restriction compared to when they had sufficient sleep. This effect was directly correlated with increases in sleepiness, as higher KSS scores were associated with feeling older. The findings highlight the immediate effect of just two nights of reduced sleep on subjective age perceptions, suggesting that sleep deprivation swiftly influences how young or old individuals feel.
The researchers also found that chronotype interacted with sleep condition to affect subjective age. Morning types, in particular, experienced a larger increase in subjective age following sleep restriction compared to evening types, indicating that the impact of sleep deprivation on subjective age may vary depending on an individual’s natural sleep-wake preferences.
Across both the cross-sectional and experimental studies, feeling extremely alert was related to feeling approximately 4 years younger than one’s actual age, while extreme sleepiness was related to feeling approximately 6 years older than one’s actual age.
“This means that going from feeling alert to sleepy added a striking 10 years to how old one felt,” Balter explained.
While the studies shed light on the significant role of sleep in feeling young, there are some limitations to consider. For instance, the research focused on sleep duration and sleepiness but did not extensively explore other dimensions of sleep health, such as sleep quality or fatigue. Additionally, the influence of seasonal variations on sleep and subjective age was not fully addressed.
Future research could examine the biological mechanisms behind sleep’s role in subjective ageing, explore the impact of sleep quality and other sleep dimensions, and investigate the effects of season and light exposure on subjective age.
Despite the limitations, the findings highlight a profound connection between sleep and our sense of youthfulness.
“Safeguarding our sleep is crucial for maintaining a youthful feeling,” Balter said. “This, in turn, may promote a more active lifestyle and encourage behaviors that promote health, as both feeling young and alert are important for our motivation to be active.”
The study, “Sleep and subjective age: protect your sleep if you want to feel young,” was authored by Leonie J. T. Balter and John Axelsson.
