A recent study published in BMJ Public Health has shed light on the connection between sleep patterns and cognitive performance. Researchers at Imperial College London found that older individuals who identify as ‘night owls’ tend to have higher cognitive scores compared to those who prefer morning activities. This finding offers new insights into how our internal biological clocks may influence brain function.
“Our interest in this topic stemmed from a broader curiosity about how lifestyle factors, particularly sleep, influence brain health. Given the ageing population and the rising prevalence of cognitive decline, understanding the relationship between sleep patterns and cognitive function could help develop better interventions and health guidelines to maintain cognitive health in older adults,” explained study authors Raha West (a NIHR Doctoral Research Fellow) and Daqing Ma (a professor of anaesthesia).
The study leveraged data from the UK Biobank, a large-scale prospective study involving over half a million participants aged 40 and above across the UK. Specifically, the analysis included 26,820 participants who had completed all necessary surveys and cognitive assessments.
Participants provided detailed information about their sleep habits, including sleep duration, chronotype, and sleep quality, through self-report questionnaires. Sleep duration was categorized into short (<7 hours), normal (7-9 hours), and long (>9 hours). Chronotype was assessed based on participants’ self-identification as either a morning person, intermediate, or evening person. Sleep quality was measured by the frequency of experiencing sleeplessness or insomnia.
The cognitive performance of participants was evaluated using a series of tests designed to assess various aspects of cognition, such as reasoning, memory, and reaction time. These tests included Fluid Intelligence (verbal and numerical questions), Pairs Matching (a memory game), Reaction Time (measured through a card game), and Prospective Memory (a task involving memory recall).
The participants were divided into two cohorts: Cohort 1 (10,067 participants) completed all four cognitive tests (Fluid Intelligence, Pairs Matching, Reaction Time, and Prospective Memory), while Cohort 2 (16,753 participants) completed only two cognitive tests (Pairs Matching and Reaction Time).
One of the key findings was the significant association between chronotype and cognitive performance. Participants who identified as evening types, or ‘night owls,’ scored higher on cognitive tests than those who identified as morning types. Intermediate types also showed better cognitive performance than morning types.
“We were particularly intrigued by the chronotype findings, which found that evening types performed better on cognitive tests in older adults, in contrast with younger populations, where morning types typically have better outcomes,” the researchers told PsyPost. “This suggests that the relationship between chronotype and cognitive function may change with age.”
Regarding sleep duration, the researchers found that normal sleep duration (7-9 hours) was associated with slightly higher cognitive scores in Cohort 1. On the other hand, long sleep duration (more than 9 hours) was linked to significantly lower cognitive scores across both cohorts. This result supports previous research indicating a U-shaped relationship between sleep duration and cognitive performance, where both insufficient and excessive sleep are associated with worse cognitive health.
“The key takeaway is that getting 7-9 hours of quality sleep per night is crucial for maintaining cognitive function,” West and Ma said. “Additionally, individuals should recognise and work with their natural sleep patterns, whether they are morning or evening types, to optimise their cognitive performance.”
Jessica Chelekis, a senior lecturer at Brunel University London (who was not involved in the study), told the Science Media Centre: “In my expert opinion, the main takeaway should be that the cultural belief that early risers are more productive than ‘night owls’ does not hold up to scientific scrutiny. While everyone should aim to get good-quality sleep each night, we should also try to be aware of what time of day we are at our (cognitive) best and work in ways that suit us. Night owls, in particular, should not be shamed into fitting a stereotype that favours an ‘early to bed, early to rise’ practice.”
While the study provides valuable insights into the relationship between sleep patterns and cognitive performance, it has several limitations. For instance, the cross-sectional design of the study prevents establishing causality.
“Without a detailed picture of what is going on in the brain we don’t know if being a ‘morning’ or ‘evening’ person affects memory and thinking, or if a decline in cognition is causing changes to sleeping patterns,” explained Jacqui Hanley of Alzheimer’s Research UK (who was not involved in the study).
Additionally, reliance on self-reported data for sleep parameters may introduce biases, and the study did not adjust for educational attainment due to incomplete data. The lack of control for the time of day during cognitive assessments and the exclusion of participants with unclear chronotypes may also affect the generalizability of the findings.
To enhance future research, it would be beneficial to include more diverse populations from different geographical locations and incorporate objective sleep measures. Longitudinal studies could provide a clearer understanding of the causal relationships between sleep patterns and cognitive performance. Furthermore, future research could explore the biological mechanisms linking sleep duration with cognitive deterioration.
“In the long term, we might explore the mechanisms behind how different chronotypes affect cognitive performance and extend this research to more diverse populations,” West and Ma said. “Understanding these mechanisms could lead to personalised sleep and health recommendations to optimise cognitive health.”
Interestingly, the study did not find a significant relationship between sleep quality, measured by the frequency of sleeplessness or insomnia, and cognitive performance. This finding contrasts with some prior studies that have shown poor sleep quality to be associated with lower cognitive functioning.
“We would like to emphasize the importance of considering both sleep duration and quality,” West and Ma noted. “While our study found significant associations with sleep duration and chronotype, the impact of sleep quality needs further investigation. Future research should also look into the effects of physical activity, diet, and social engagement on sleep and cognitive health.”
The study, “Sleep duration, chronotype, health and lifestyle factors affect cognition: a UK Biobank cross-sectional study,” was published July 10, 2024.
