new research suggests.
“Rather than just being personal preferences, these chronotypes could impact our cognitive function,” said study investigator, Raha West, MBChB, with Imperial College London, London, England, in a statement.
But the researchers also urged caution when interpreting the findings.
“It’s important to note that this doesn’t mean all morning people have worse cognitive performance. The findings reflect an overall trend where the majority might lean toward better cognition in the evening types,” Dr. West added.
In addition, across the board, getting the recommended 7-9 hours of nightly sleep was best for cognitive function, and sleeping for less than 7 or more than 9 hours had detrimental effects on brain function regardless of whether an individual was a night owl or lark.
The study was published online in BMJ Public Health.
A UK Biobank Cohort Study
The findings are based on a cross-sectional analysis of 26,820 adults aged 53-86 years from the UK Biobank database, who were categorized into two cohorts.
Cohort 1 had 10,067 participants (56% women) who completed four cognitive tests measuring fluid intelligence/reasoning, pairs matching, reaction time, and prospective memory. Cohort 2 had 16,753 participants (56% women) who completed two cognitive assessments (pairs matching and reaction time).
Participants self-reported sleep duration, chronotype, and quality. Cognitive test scores were evaluated against sleep parameters and health and lifestyle factors including sex, age, vascular and cardiac conditions, diabetes,alcohol use, smoking habits, and body mass index.
The results revealed a positive association between normal sleep duration (7-9 hours) and cognitive scores in Cohort 1 (beta, 0.0567), while extended sleep duration negatively impacted scores across in Cohort 1 and 2 (beta, –0.188 and beta, –0.2619, respectively).
An individual’s preference for evening or morning activity correlated strongly with their test scores. In particular, night owls consistently performed better on cognitive tests than early birds.
“While understanding and working with your natural sleep tendencies is essential, it’s equally important to remember to get just enough sleep, not too long or too short,” Dr. West noted. “This is crucial for keeping your brain healthy and functioning at its best.”
Contrary to some previous findings, the study did not find a significant relationship between sleep, sleepiness/insomnia, and cognitive performance. This may be because specific aspects of insomnia, such as severity and chronicity, as well as comorbid conditions need to be considered, the investigators wrote.
They added that age and diabetes consistently emerged as negative predictors of cognitive functioning across both cohorts, in line with previous research.
Limitations of the study include the cross-sectional design, which limits causal inferences; the possibility of residual confounding; and reliance on self-reported sleep data.
Also, the study did not adjust for educational attainment, a factor potentially influential on cognitive performance and sleep patterns, because of incomplete data. The study also did not factor in depression and social isolation, which have been shown to increase the risk for cognitive decline.
No Real-World Implications
Several outside experts offered their perspective on the study in a statement from the UK nonprofit Science Media Centre.
The study provides “interesting insights” into the difference in memory and thinking in people who identify themselves as a “morning” or “evening” person, Jacqui Hanley, PhD, with Alzheimer’s Research UK, said in the statement.
However, without a detailed picture of what is going on in the brain, it’s not clear whether being a morning or evening person affects memory and thinking or whether a decline in cognition is causing changes to sleeping patterns, Dr. Hanley added.
Roi Cohen Kadosh, PhD, CPsychol, professor of cognitive neuroscience, University of Surrey, Guildford, England, cautioned that there are “multiple potential reasons” for these associations.
“Therefore, there are no implications in my view for the real world. I fear that the general public will not be able to understand that and will change their sleep pattern, while this study does not give any evidence that this will lead to any benefit,” Dr. Cohen Kadosh said.
Jessica Chelekis, PhD, MBA, a sleep expert from Brunel University London, Uxbridge, England, said that 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 favors an ‘early to bed, early to rise’ practice,” Dr. Chelekis said.
Funding for the study was provided by the Korea Institute of Oriental Medicine in collaboration with Imperial College London. Dr. Hanley, Dr. Cohen Kadosh, and Dr. Chelekis have no relevant disclosures.
A version of this article first appeared on Medscape.com.