The Study
A Systematic Review of Literature on the Association Among Sleep, Cortisol Level and Cardiovascular Health Within the Healthcare Shift Worker Population
This study looked at lots of other studies and found that people who work nights often have worse sleep, weird cortisol levels, and more heart problems—but it doesn’t prove that one causes the other. It’s like noticing that people who eat a lot of candy also get more cavities; it doesn’t mean candy causes cavities, just that they often happen together.
Analysis score
Maximum 85 for a systematic review.
Where the score came from
When people work nights or rotate shifts, their body’s internal clock gets confused, which messes up sleep and stress hormones like cortisol.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 526 / 100
Quality score
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes — these changes are linked to real health risks like heart disease, even after accounting for age and weight.
- 2Night shift workers have lower morning cortisol, higher evening cortisol, worse sleep, lower heart rate variability, and a 66% higher heart disease risk if they also have insomnia.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Biomedicines
Year
2025
Authors
Aslah Nabilah Abdull Sukor, N. Juliana, Nazefah Abdul Hamid, N. Teng, Muslimah Ithnin, S. Azmani, S. Kasim
Related Content
Claims (5)
People who work nights or irregular shifts in healthcare tend to have less healthy heart rhythms, which means their hearts aren't recovering as well—and this is linked to a higher chance of heart problems, even if they're young or live a healthy lifestyle.
People who work night shifts or irregular hours tend to have weird cortisol patterns—low in the morning and high at night—which seems to make their sleep worse. This might be because their body’s internal clock is out of sync with their work schedule.
Nurses who work nights and have trouble sleeping are much more likely to develop heart problems, even when you account for their age, weight, and work hours—suggesting that just having insomnia might be a hidden danger for their hearts.
Working irregular shifts messes up your body clock, which makes it harder to sleep well. Poor sleep raises a stress hormone called cortisol, which then makes your sleep and heart function even worse over time — raising your risk of heart problems.
When your body's internal clock is out of sync—like from shift work or jet lag—it messes up your stress hormones, stops your sleep hormone from working right, and turns on inflammation in the same way that being tired or stressed for a long time does.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.