July 11, 2024

expert reaction to study on sleep, chronotype and cognition

A study published in BMJ Public Health looks at the association between sleep duration, chronotype and cognitive function.

Dr Jacqui Hanley, Head of Research Funding at Alzheimer’s Research UK said:

“This large study looked at the complex interaction between people’s sleep patterns and memory and thinking ability. Previous studies have suggested that sleeping too little, but also too much, can impact cognition. But this study provides interesting insights into the difference in memory and thinking in people who identify themselves as a “morning” or “evening” person.

“However, it’s difficult to study people’s sleeping patterns over a long period of time as part of a clinical trial. Researchers were relying on people self-reporting their sleeping habits and this can lead to errors as people tend to over or underestimate how well they slept. Without a detailed picture of what is going on in the brain we also 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. Further research is needed to consider how other lifestyle factors are playing into what we are seeing, and to gain a better understanding of the underlying mechanisms in the brain that are causing cognitive changes.”

Professor Roi Cohen Kadosh, Head of School of Psychology, Professor of Cognitive Neuroscience, University of Surrey, said:

“This is a solid research, although some of the data is not objective (sleep data is self-report and there is a need for an objective data), but overall, it is a very large sample size, and a fantastic highlight of the potential of the UK Biobank to lead to discoveries. Having said that the press release is inaccurate. This study cannot tell us anything about the impact of sleep on cognition, and a title like “make you sharper” is wrong. It can of course tell us about the association of sleep with cognition but not any causal effect. There are multiple potential reasons for such associations. Also, the scientists in their wording provide such an impression for the public as some of the sentences in their paper hint at such causality “The significant influence of sleep chronotypes on cognitive function adds new depth to our understanding of the role of sleep in cognitive health.” (P. 1), while in other places they stated that their results allow to infer only an association. 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 (aside from the effect size that is small). Therefore, there are no implications in my view for the real world, and I think that a policy intervention based on this study (as the co-study leader suggests) is premature and a different research, with a different design is required to justify that. We need the right design to allow causation, and this study unfortunately lacks that.”

Dr Jessica Chelekis, Senior Lecturer in Sustainability Global Value Chains and a sleep expert from Brunel University London, said:

“’Being a night owl might make you sharper’ exaggerates the takeaway. While the study design is fine, there are important limitations. One in particular, not addressed by the authors, puts the results regarding chronotype and cognitive ability into question. The most important one is that the authors never state what time of day the participants took part in the cognitive tests, which could have serious implications for their results. In addition, the authors also state that they did not take into account the educational attainment of the participants.

“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.”

‘Sleep duration, chronotype, health and lifestyle factors affect cognition: a UK Biobank cross- sectional study’ by Raha West et al. was published in BMJ Public Health at 00:05 UK time on Thursday 11 July.

DOI: 10.1136/bmjph-2024-001000

Declared interests

Professor Roi Cohen Kadosh: None

Dr Jessica Chelekis: No declarations of interest