Early Bird or Night Owl: Who’s Mentally Sharper?
By Seema Gupta, MD, MSPH
SYNOPSIS: A large cross-sectional analysis of adults aged 53-86 years found that people with normal sleep durations while being “night owls” often scored higher on cognitive tests than “early bird” types.
SOURCE: West R, Wong RTC, Park J-E, et al. Sleep duration, chronotype, health and lifestyle factors affect cognition: A UK Biobank cross-sectional study. BMJ Public Health 2024;2:e001000.
Sleep is an essential and involuntary process that is vital for maintaining mental and physical health. Emerging evidence suggests that sleep may be crucial for a number of bodily functions, including learning and memory consolidation, judgment and decision-making, emotional regulation, and bodily restoration.1 Current evidence also has demonstrated a bidirectional link between sleep and immunity.2
Activation of the immune system can alter sleep regulation while, in turn, sleep impairment may lead to chronic and systemic low-grade inflammation, which is associated with various metabolic, autoimmune, and vascular diseases.3 The quality and duration of sleep may influence the risk of cognitive decline, with both short (≤ 4 hours) and long (≥ 10 hours) sleep durations being associated with cognitive impairments.4 There also seems to be a relation between sleep quality and cognitive performance, with poor sleep quality being correlated with lower cognitive functioning.5
Similar to sleep duration and quality, an individual’s sleep pattern (chronotype) — indicating at what time the person prefers to go to sleep — also may be a determining factor. However, not much is known regarding the effect of chronotypes or circadian rhythms on cognition.
In their study, West et al attempted to explore the relationship between sleep patterns, chronotypes, sleep quality, and the influence of health and lifestyle factors on cognitive performance. They analyzed data from a United Kingdom Biobank database consisting of 26,820 individuals between the ages of 53 and 86 years. Study participants were categorized into two cohorts. Cohort 1 included 10,067 individuals (56% women) who completed four cognitive tests measuring fluid intelligence/reasoning, pairs matching, reaction time, and prospective memory. Cohort 2 included 16,753 individuals (56% women) who completed only two cognitive assessments (pairs matching and reaction time). Participants self-reported sleep duration, chronotype, and quality. Cognitive test scores were evaluated for sleep parameters as well as a number of health and lifestyle factors that included sex, age, vascular and cardiac conditions, diabetes, alcohol use, smoking habits, and body mass index.
Researchers found a positive association between normal sleep duration (seven to nine hours) and cognitive scores in cohort 1 (β = 0.0567; 95% confidence interval [CI], 0.0284 to 0.0851), while extended sleep duration negatively affected scores across in Cohorts 1 and 2 (cohort 1: β = −0.188; 95% CI, −0.2938 to −0.0822; cohort 2: β = −0.2619; 95% CI, −0.3755 to −0.1482). A study participant’s preference for evening or morning activity correlated strongly with their test scores. Specifically, evening types (“night owls”) consistently performed better on cognitive tests than morning types (“early birds”). Night owls scored about 13.5% higher on their test scores than early birds in one group and 7.5% higher than morning types in another group. Intermediate sleepers (a combination of evening types and morning types) also scored 10.6% and 6.3% higher, respectively, than morning types in the two groups. These differences were statistically significant.
Cohort 1 participants with normal sleep durations (seven to nine hours) had higher cognitive scores than those who slept for shorter durations. Abnormally long sleep durations were associated with lower cognitive scores in both cohorts as compared to those with normal sleep patterns. Additionally, female sex, increased age, and having a diagnosis of angina, hypertension, and diabetes also worsened cognitive performance.
Commentary
It is clear that sleep is vital not only for survival, but it provides a restorative and protective function on cognition by the removal of toxic metabolites from the central nervous system. However, in contrast to studies that showed morning-type adolescents have much-improved health and mental well-being compared with evening-type adolescents, West et al have demonstrated the opposite findings for people aged 53-86 years. In their study, it seems that those who are more active in the evening may perform better on cognitive tests than those who are more active in the morning hours. It is interesting to note that the average age of study participants was quite advanced — 71 and 72 years in cohorts 1 and 2, respectively.
While the study may not be adequate to begin recommending changes in sleeping habits, there are three clear takeaways. First, a good night’s sleep of adequate duration (seven to nine hours) remains critical to good cognitive health and functioning. Second, optimal management of chronic health conditions and a healthy lifestyle is important in preserving one’s cognitive performance. And lastly, the cultural belief that “early birds” are more productive than “night owls” may be true in early and adolescent life, but not necessarily later in life.
Seema Gupta, MD, MSPH, is Clinical Assistant Professor, Department of Family and Community Health, Joan C. Edwards School of Medicine, Marshall University, Huntington, WV.
References
- Vandekerckhove M, Wang Y-L. Emotion, emotion regulation, and sleep: An intimate relationship. AIMS Neurosci 2017;5:1-17.
- Besedovsky L, Lange T, Haack M. The sleep-immune crosstalk in health and disease. Physiol Rev 2019;99:1325-1380.
- Rogers NL, Szuba MP, Staab JP, et al. Neuroimmunologic aspects of sleep and sleep loss. Semin Clin Neuropsychiatry 2001;6:295-307.
- Ma Y, Liang L, Zheng F, et al. Association between sleep duration and cognitive decline. JAMA Netw Open 2020;3:e2013573.
- Li M, Wang N, Dupre ME. Association between the self-reported duration and quality of sleep and cognitive function among middle-aged and older adults in China. J Affect Disord 2022;304:20-27.
A large cross-sectional analysis of adults aged 53-86 years found that people with normal sleep durations while being “night owls” often scored higher on cognitive tests than “early bird” types.
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