Don´t we all want to feel young and rejuvenated? Recent findings suggest that this aspiration may have valuable benefits when it comes to challenging the passage of time and aging. Feeling younger has been linked to brain health, as shown by research indicating that older adults who feel younger have a younger predicted brain age and greater gray matter volume in various brain regions. In light of this connection, we set out to explore whether sleep, a fundamental process essential for brain function and overall well-being, holds any secrets to feeling young.
Subjective age, often referred to as how old we feel, is a concept that goes beyond mere perception. It turns out that feeling younger than our actual age is associated with a longer life, better physical and mental health, and more positive psychological traits (such as optimism, hope, and resilience). This has led to suggestions that subjective age be included as a biophysical marker of aging as part of health assessments.
Many people feel younger than their chronological age. While this phenomenon is less common among younger people, the gap between our actual age and how old we feel becomes more pronounced as we reach our thirties and beyond. Emerging research suggests that our sleep habits may play a role in shaping the age we feel. Sleep is crucial not only for physical well-being but also for mental health. During sleep, the brain undergoes essential processes, including the clearing of metabolic waste, the replenishment of proteins at synapses, and memory consolidation. Although it is undeniable that sleep is fundamental for health, its relevance to feeling youthful has received limited attention. There is some evidence that people who feel subjectively older experience poorer sleep quality or have sleep difficulties, both in cross-sectional and longitudinal studies, although this may largely be limited to older women. Sleep is a highly dynamic process, with gradual changes over a lifetime, but it also varies day to day. Recognizing the essential role of sleep in well-being, we conducted two studies—one cross-sectional and one experimental—to examine how sleep in the past month and more acute sleep loss influence subjective age. Exploratory analyses were also conducted to assess the influence of chronotype on the relationship between sleep and subjective age.
The current studies examined the impact of insufficient sleep and drowsiness on the subjective experience of age.
Study 1, a cross-sectional study of 429 participants (282 women (66%), 144 men, 3 of another gender; age range 18–70), found that each additional day of insufficient sleep in the past 30 days increased subjective age by 0.23 years.
Study 2, a crossover experimental study on sleep restriction (n = 186; 102 women (55%), 84 men; age range 18–46), showed that two nights of sleep restriction (4 hours in bed each night) made people feel 4.44 years older compared to sleep saturation (9 hours in bed per night). Additionally, shifting from feeling extremely alert (score of 1 on the Karolinska Sleepiness Scale (KSS)) to feeling extremely drowsy (score of 9 on the KSS) was associated with feeling 10 years older in both studies.
These findings provide compelling support that insufficient sleep and drowsiness have a substantial influence on how old we feel, and that protecting sleep is likely a key factor in feeling young.
Both studies, one cross-sectional and one experimental, demonstrate that sleep and drowsiness play a profound role in shaping our sense of age. The findings revealed that insufficient sleep and drowsiness made people feel older than their actual age, supporting that a good night´s sleep is crucial for feeling younger than one´s actual age.
Analyses also showed that the importance of sleep for subjective age increases with advancing age, that the relationships hold true for both prolonged periods of insufficient sleep and even just two nights of insufficient sleep, that drowsiness is likely a mediator for feeling older, and that the relationship between lack of sleep and feeling older is causal and driven by drowsiness. While prior literature has shown that feeling older is associated with poorer sleep quality, our data indicate that sleep may be more important for subjective age than vice versa. These findings support that sleep, a vital biological phenomenon, could be key to feeling young.
Although sleep serves various restorative functions, the biological mechanisms behind its role in influencing subjective age are likely multifaceted and challenging to investigate. This complexity is particularly evident since feeling young is associated with multiple aspects, including well-being, better brain health, and feeling energized. Existing evidence suggests that sleep disturbances could accelerate biological aging, such as telomere shortening and cellular senescence. Future studies may further assess to what extent these mechanisms also predict subjective aging.
It has previously been shown that drowsiness strongly influences motivation to be socially and physically active, making it a possible mediator through which insufficient sleep reduces the feeling of youth. Since drowsiness can be easily influenced and altered, interventions involving daylight exposure or caffeine consumption could potentially lead to feeling younger. This, in turn, may encourage a more active lifestyle and foster health-promoting behaviors.
This expands on previous research showing that taking a memory test can make people feel older, though only in older adults. Considering that both sleep and drowsiness are modifiable factors, these discoveries open up new possibilities for fostering a sense of youth and facilitating associated benefits, such as a more active lifestyle and embracing new challenges.
We found no gender associations in either of our two studies (one conducted in Sweden and another in the UK), which aligns with some previous findings. This differs from other studies that have found women feel subjectively younger than men, particularly older women, though the opposite has also been reported: women feel subjectively older than men.
A limitation of the included studies is that they focus only on a few dimensions of sleep health. The present study primarily focused on how sleep duration, sleep insufficiency, and drowsiness influence subjective age, and future studies could evaluate how other dimensions of sleep health, such as tiredness, fatigue, and sleep quality, might also influence subjective age. Exploratory analyses indicated that evening chronotypes felt subjectively older than morning and intermediate chronotypes, but morning chronotypes reported the greatest increase in subjective age following sleep restriction.
In conclusion, our studies provide compelling evidence that sleep and drowsiness have a strong impact on how old we feel, and that protecting sleep is likely a key factor in feeling young.
