Cohort studyindependent cross-checkabstract checked★ key study I-LIFE-109 standard review
Night owls and heart disease
Chronotype, Life's Essential 8, and Risk of Cardiovascular Disease: A Prospective Cohort Study in UK Biobank.
Overview
Kianersi S et al.. J Am Heart Assoc 2026 · PMID 41603783 · DOI 10.1161/JAHA.125.044189
'Night owls' had a 16% higher risk of heart attack or stroke, mostly because of less healthy habits.
Does the study support the specific claim? No · Methodological quality: moderate
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Link chronotype to CVD.
- How was the study done?
Cohort of 322,777 UK adults.
- How many people, animals or samples were studied?
UK Biobank.
- What was actually found?
HR 1.16; 75% mediated by LE8.
- How large was the observed effect?
HR 1.16 (1.10-1.22).
- What do the results mean in everyday life?
Late-night lifestyles tend to come with less healthy habits.
- What are the study's limitations?
Observational.
- What does it say about Elawady's specific claim?
Partly contradicts 'staying up late is not harmful'.
- Do the results apply to Germany and Europe?
Applies; same physiology.
- What can explicitly not be concluded from this study?
Causal effect of bedtime itself.
Scientific in-depth review
1. Full reference
- Authors
- Kianersi S et al.
- Journal
- J Am Heart Assoc
- Year
- 2026
- Identifier
- PMID 41603783 DOI 10.1161/JAHA.125.044189
- Verification
- verified – PubMed efetch 2026-10-26; Crossref update-to/updated-by check
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
One author reports consultancy fees from Eli Lilly and stock in GSK (stated).
2. Research question
Is evening chronotype associated with CVD and is this mediated by cardiovascular health (LE8)?
3. Study design and population
- Study design
- Cohort study – Prospective cohort with mediation analysis
- Population
UK Biobank participants aged 39-74 without CVD
- Country
UK
- Period
not stated in abstract
- Sample size
322,777; 17,584 CVD events over median 13.8 years
- Inclusion and exclusion criteria
not stated in abstract
4. Methods and endpoints
- Exposure / intervention
Self-reported chronotype ('definite evening')
- Comparator
Intermediate chronotype
- Endpoints
Incident MI or stroke
- Statistical methods
Cox models; mediation
5. Actual results
- Results
Definite evening vs intermediate: total CVD HR 1.16 (95% CI 1.10-1.22); 79% higher prevalence of poor LE8 score; LE8 explained 75% of the association (indirect effect HR 1.11, 1.09-1.13).
- Absolute risks
not reported
- Authors' conclusion
Individuals with an evening chronotype may particularly benefit from interventions targeting CVD risk factors.
6. Strengths
- Very large cohort, long follow-up
7. Weaknesses
- Chronotype by one question
- Observational; UK Biobank healthy-volunteer bias
8. Risk of bias
- Orienting tool
- ROBINS-E
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- some concerns
- Rationale
Observational; confounding.
9. Assessment of the statistical interpretation
Most of the association runs through modifiable risk factors (stats/I-LIFE-109_chronotype.py).
10. Relevance to the specific claim
Being a 'night person' is linked to modestly higher CVD risk mostly via worse lifestyle factors - late habits are not proven harmless, but timing itself is not proven harmful.
11. Independent contrary findings
12. Transferability to Germany and Europe
Universal biology; applies in Europe and Egypt.
13. Overall methodological judgement
Indirect, modest contradicting evidence; mostly mediated.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | moderate |
| Risk of bias | some concerns |
| Precision of results | high |
| Directness | indirect |
| Reproducibility | partly replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
- Staying up late is not harmful and eight hours of sleep are not needed; those who say staying up late is harmful 'have not understood the philosophy of the Creator'. – Studies contradicting or limiting the claim