Strict morning people carried higher heart attack risk than intermediate types

"Morning person" is often treated as shorthand for healthy habits, while "night owl" carries connotations of worse cardiovascular and metabolic outcomes. A study published this month in Sleep Health, using over a decade of follow-up from the Sleep Heart Health Study, tests that assumption directly — and finds it more complicated than the stereotype suggests [s1].

The design

Researchers analyzed 4,578 adults aged 40 and older from the Sleep Heart Health Study [s1]. Chronotype — a person's natural circadian preference for earlier or later sleep-wake timing — was derived using the standard Munich Chronotype Questionnaire algorithm applied to self-reported bedtimes and wake times, then categorized into morning, intermediate, or evening type [s1]. Incident myocardial infarction events were tracked and adjudicated over a mean follow-up of 10.6 years [s1]. Cox proportional hazards models estimated hazard ratios, adjusting for demographic, lifestyle, cardiometabolic, and polysomnography-derived sleep parameters, with stratified analyses examining whether the pattern differed by obstructive sleep apnea status [s1].

What it found

Compared with intermediate chronotypes — the reference group — both morning types (hazard ratio 1.50, 95% CI 1.10–2.05) and evening types (hazard ratio 1.40, 95% CI 1.00–1.95) showed significantly higher myocardial infarction risk after full adjustment [s1]. Notably, the morning group did not show the lowest risk, despite being the chronotype most commonly associated with healthy, disciplined habits [s1].

The association was substantially stronger among participants who also had obstructive sleep apnea: within that subgroup, the hazard ratios rose to 1.85 for morning types and 1.82 for evening types, while no significant chronotype-related risk difference was observed among participants without sleep apnea [s1].

Why "intermediate is safest" is the counterintuitive headline

The finding that intermediate chronotype carried the lowest myocardial infarction risk — with both morning and evening extremes showing elevated risk — directly challenges a common cultural assumption that early rising is inherently the healthiest circadian pattern. The study's authors state this explicitly: "these findings suggest that extreme chronotypes may be less favorable for cardiovascular health" [s1], framing risk as a function of distance from a moderate midpoint rather than a simple morning-good, evening-bad spectrum.

Why the sleep apnea interaction is the more clinically useful part of this finding

That the chronotype-cardiovascular risk association essentially disappeared among participants without obstructive sleep apnea, while nearly doubling in relative terms among those with it, suggests chronotype extremes may matter most as a risk amplifier specifically in people who already have disordered breathing during sleep — rather than as an independent cardiovascular risk factor that applies uniformly to everyone regardless of other sleep pathology. That's a more targeted, actionable framing than "extreme chronotypes are bad for the heart" as a blanket statement: the risk concentration in the sleep-apnea subgroup points toward chronotype as a modifier of existing sleep-apnea-related cardiovascular risk, rather than a standalone independent threat in an otherwise healthy sleeper.

What this doesn't establish

This is an observational cohort study — even with adjustment for numerous demographic, lifestyle, cardiometabolic, and sleep-related factors, it cannot establish that chronotype itself causally drives myocardial infarction risk, as opposed to chronotype correlating with some other unmeasured behavioral or biological factor. Chronotype was derived from self-reported bedtimes and wake times via a standard questionnaire algorithm rather than objectively measured through actigraphy or biomarkers, introducing standard self-report limitations. The Sleep Heart Health Study cohort, while a well-established longitudinal dataset, represents a specific population enrolled decades ago for sleep research purposes, which may not fully generalize to younger populations or those with different demographic profiles.

What the researchers suggest this could mean for practice

The study's authors propose that incorporating chronotype into cardiovascular risk stratification, particularly for patients already known to have obstructive sleep apnea, could improve myocardial infarction prevention strategies [s1] — a forward-looking suggestion based on this single cohort's findings rather than an established clinical practice.

What to watch

Whether the intermediate-chronotype-is-safest pattern, and the sleep-apnea interaction specifically, replicate in other cohorts, and whether chronotype assessment eventually becomes a standard part of cardiovascular risk evaluation for sleep apnea patients. This article is not medical advice.

Sources

1. Circadian preference and risk of myocardial infarction: Findings from a longitudinal community-based study — Sleep Health, 24 July 2026