Are naps good for you?

Using UK Biobank data on 378,932 people, researchers instrumented "habitual daytime napping" with 92 genome-wide genetic variants already linked to it, then used Mendelian randomization — a method that uses genes as a natural experiment to get closer to cause and effect than an ordinary observational study can. Genetic liability to napping was linked to larger total brain volume (+15.8 cm³, about 1.3% larger, 95% CI 0.25 to 31.34) but not to hippocampal volume, reaction time, or visual memory [4]. The "2.6 to 6.5 years younger" framing comes from the study's own press release, converting that 15.8 cm³ using published rates of age-related brain-volume loss — a real, if rough, translation, but one the paper itself does not test against actual cognitive decline, dementia, or death. The authors' own conclusion calls the link "modest" and says it needs replication.

The largest and most recent pooled look combined 21 cohort studies covering 374,306 adults across 11 countries. Any self-reported napping, regardless of length, was linked to 28% higher all-cause mortality than not napping (hazard ratio 1.28, 95% CI 1.18–1.38). Splitting by duration is where the story clarifies: naps under an hour showed no increase at all (hazard ratio 1.00, 95% CI 0.90–1.11), while naps of an hour or more carried 22% higher all-cause mortality (hazard ratio 1.22, 95% CI 1.12–1.33) and 37% higher cardiovascular mortality (hazard ratio 1.37, 95% CI 1.09–1.71) [1].

A decade before Wang, a meta-analysis of 11 prospective cohorts covering 151,588 adults found nearly the same shape: naps of 60 minutes or more carried 27% higher all-cause mortality (RR 1.27, 95% CI 1.11–1.45) and 82% higher cardiovascular mortality (RR 1.82, 95% CI 1.22–2.71); naps under 60 minutes did not reach statistical significance for either outcome. Modeling the dose-response curve directly, cardiovascular risk followed a J-shape — falling from 0 to about 30 minutes, then climbing sharply past roughly 45 minutes — while all-cause mortality rose in a straight line, about 4% for every extra 10 minutes of napping [2].

A meta-analysis of 11 randomized and crossover studies (381 participants) found daytime naps improved alertness afterward, effect size 0.29 (95% CI 0.10–0.48), with naps started before 1pm outperforming later ones. Studied nap lengths ranged 15 to 90 minutes, averaging about 55 minutes, and duration itself did not change how much the alertness benefit was — the boost showed up whether the nap was short or longer, as long as it was timed earlier in the day [3]. None of this is mortality evidence; it is a completely separate outcome, measured hours later, not decades later.

Using the same formula YapSpan applies wherever a mortality hazard ratio exists (years = −8 × log2 of the hazard ratio), Wang's 60-plus-minute all-cause hazard ratio of 1.22 works out to about −2.3 years. That number is shown here for scale, not on the Life Quiz: both mortality papers are observational, and both explicitly flag that long napping is plausibly a symptom rather than a cause — of undiagnosed sleep apnea, depression, poor night sleep, or illness already in progress, all of which independently shorten life and independently make people nap longer. Neither meta-analysis can fully separate "napping causes this" from "being unwell causes both the napping and the risk." That is a reason to read the −2.3 years with real caution, not a reason to erase it.

Putting the two mortality meta-analyses and the alertness data together: no nap is neutral. A short nap, roughly 10 to 30 minutes, taken in the early afternoon, sits in the range with alertness benefits and no mortality signal in either cohort. A medium nap, 30 to 59 minutes, is still inside Wang's "no increase" band by the categorical cutoff, but Yamada's dose-response curve was already climbing by then — worth noticing, not panicking about. A long nap, 60 minutes or more, is where every mortality number above turns up, in both meta-analyses, independently.

Both cohort papers point the same direction without proving it directly: a sudden or persistent hour-plus napping habit is a plausible marker of poor night sleep, depression, or undiagnosed conditions like sleep apnea, all of which have their own, better-established mortality evidence. Simply willing yourself to nap for less time does not address any of those, if one is present.