Daytime Napping and Brain Volume: Revisiting the 2023 Study

In 2023, ANI reported a study on daytime napping by researchers affiliated with University College London and the University of the Republic in Uruguay. It linked a genetic tendency to nap with larger total brain volume.

How did researchers study habitual daytime napping?

According to ANI's account, the study used genetic data from up to 378,932 UK Biobank participants. The reported age range was 40 to 69. That puts the sample within a life stage relevant to many men reading about memory and healthy aging.

The team used a method called Mendelian randomization. It uses genetic variants as tools for examining a possible causal link between an exposure and an outcome. Here the exposure was a genetic tendency toward habitual daytime napping. The outcomes were measures of brain structure and thinking.

The analysis used 97 DNA variants associated with the likelihood of habitual napping. The researchers asked whether that genetic tendency was linked to the brain and cognitive measures they examined. This was an attempt to move beyond a simple comparison of people who nap with people who do not.

That distinction matters when reading the word “causal.” The question was about a genetic propensity for a behavior, not the effect of adding an afternoon rest to a person's schedule.

This was not a trial that assigned people to nap or stay awake for a set period. There was no nap intervention with a treatment duration to report. Its design addressed a possible relationship between napping tendency and measured outcomes rather than tracking a prescribed nap routine.

What did the study find about brain volume and thinking?

ANI reported a positive result for total brain volume. The other reported outcomes did not show matching differences:

• Total brain volume: A genetic propensity for habitual napping was associated with larger total brain volume.
• Hippocampal volume: The analysis did not find a corresponding difference.
• Reaction time: The analysis did not find a difference in this reported cognitive measure.
• Visual processing: The analysis did not find a difference in this reported cognitive measure.

These findings need to stay separate. A positive result for total brain volume does not turn the other results into positive findings. Reading the full set of outcomes gives a more useful account of the study than treating every measure as evidence of the same benefit.

Lead author Valentina Paz described the work as the first study to attempt to untangle a causal relationship between habitual daytime napping and cognitive and structural brain outcomes. The contribution was the attempt to clarify that relationship through genetics.

What are the main limits of this finding?

Several boundaries shape how this result should be read.

• The genetic method has conditions. A causal interpretation depends on the genetic variants acting as valid tools for studying napping. The approach supports a causal reading under its assumptions rather than settling the question by itself.
• Nap duration was missing. The researchers did not have information on how long participants napped. This leaves the study unable to identify an ideal nap length or support a particular nap schedule.
• The ancestry group was limited. ANI reported that participants were of white European ancestry. The findings may not apply in the same way to people from other ancestry groups.
• Brain volume is not a clinical benefit. Total brain volume is a structural marker. It is not direct evidence of better memory or preserved independence. The study also does not establish that napping prevents cognitive decline or dementia.
• The reason for napping was not resolved. The study does not explain why a person naps or establish whether their daytime sleepiness reflects a sleep or health issue. A frequent need for daytime sleep should not be treated as evidence of protection.

The researchers described the estimated brain-volume difference as equivalent to 2.6 to 6.5 years of age-related brain-volume change. That was a way of expressing the estimated structural difference. It was not a measurement of years regained through a nap habit or evidence that someone's brain had become younger.

Senior author Dr. Victoria Garfield used cautious language. She said short daytime naps “may be a part of the puzzle” for some people seeking to preserve brain health as they age. The phrase places napping within an open research question rather than presenting it as an established intervention.

Does this change nap advice for men after 45?

For men after 45, the useful takeaway is a more precise way to read brain-health news. Start with the outcome the researchers measured. Then look at how the study examined it. Only after that comes the question of whether the result supports changing a daily habit.

In this case, the sensible response is proportionate: treat the result as a research signal rather than a new daily target. Someone who does not nap has not been given a reason by this study to begin a nap routine. Someone who already naps has not been given a scorecard showing whether that habit is right for their individual situation.

The same reading habit is useful with research on fitness and brain structure and studies of rest after sleep loss. Keeping the research question in view helps avoid treating different studies as if they tested the same thing. A study's relevance comes from its actual design and outcomes rather than the appeal of its headline.

If daytime sleepiness, memory changes or trouble focusing are a personal concern, discuss them with a qualified health professional. Use this study as context for a question rather than as an explanation for symptoms. Decisions about an individual's sleep or health need more than a headline about a group-level association.

What this changes: This study adds a genetic clue about brain structure but does not establish a new best practice for daytime napping.

How Everfitguys helps

Larger brain volume is a measurable finding, but remaining mentally sharp is the outcome that gives this topic its relevance for Everfitguys readers. Everfitguys translates health research for men in midlife and beyond who care about keeping their capacity for work, sport and family life.

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Sources

1. Study reveals regular naps linked to increased brain volume