Night owls have higher CV risks – why?

24th February 2026, A/Prof Chee L Khoo

Night owl

People on shift work are at higher risk of cardio-metabolic dysfunction including cardiovascular (CV) diseases. People on rotating day and night shifts are even worse because their body has to adapt to a new time clock every couple of weeks. These people include ambulance officers, police officers and hospital doctors! Some of us may not be shift workers but are late owls. These include the current generation of young people. Of course, many of these people also have poor dietary habits and have difficulty getting out to exercise in the morning. So, when a new study came out with the headline “night owls may face significantly higher CV risks”, we have to unpack the study.

Chronotypes

Chronotype is an individual’s natural inclination for sleep–wake timing. It reflects inherent circadian preferences and may be a marker for underlying circadian misalignments (1). In general, ~ 8-11% of middle‐aged to older adults exhibit an evening chronotype, characterised by late‐night bed time and peak activity later in the day, and ~ 24-35% have a morning chronotype, with earlier bedtimes and peak activity in the morning; the rest fall somewhere in between (intermediate) (2,3).

Using the intermediate chronotype as a comparison, adults with an evening chronotype (and plausibly those with an extreme morning chronotype) are at higher risk of circadian misalignment due to the mismatch between their internal circadian rhythms and external natural and social environment, such as work schedules (4). Circadian misalignment can affect behavioural rhythms and impair reward‐related brain functions (5). This can potentially lead to unhealthy lifestyle behaviours such as irregular sleep patterns (6), poor diet quality, heavy alcohol drinking (7), and smoking (8).  It is also associated with mood disorders and psychological distress, including depression and anxiety, which are independent CVD risk factors (9-11).

 Further, metabolically, by altering expression of clock genes, disrupting hypothalamic–pituitary–adrenal axis activity, impairing metabolic regulation, compromising platelet aggregation and coagulation, and increasing sympathetic nervous system activation, circadian misalignment might lead to dysregulation of blood pressure, glucose, and lipid profiles (12-14).

So, it is not surprising that the evening chronotype is associated with higher risk of CVD. Yet, a review of 14 systematic reviews on observational studies and 11 Mendelian randomization (MR) studies investigating the association between sleep traits, cardiometabolic risk, and CVD concluded that the role of chronotype in these associations is inconclusive (15). You can imagine the number of confounding factors you have to allow for in these studies.

Kianersi S et al used data from the UK Biobank. 322,777 participants aged 39-74 years who were free of known cardiovascular disease (CVD) were prospectively recruited (16). They categorised participants into whether they were evening or morning or in-between chronotype. They utilised the Life Essential 8 (LE8) as an assessment tool for a comprehensive measure of cardiovascular health. The authors aimed to (1) evaluate the associations of chronotype with the LE8 score and its individual components, and (2) examine the extent to which LE8 mediates the prospective association between chronotype and CVD risk.

The components of LE8 include 8 components of cardiovascular health (17):

Behavioural Factors:

  • Healthy diet
  • Participation in physical activity
  • Avoidance of nicotine
  • Healthy sleep

Health Factors:

  • Healthy weight
  • Healthy levels of blood lipids
  • Healthy levels of blood glucose
  • Healthy levels of blood pressure.

Each metric has a new scoring algorithm ranging from 0 to 100 points, allowing generation of a new composite cardiovascular health score (the unweighted average of all components) that also varies from 0 to 100 points. Extensive evidence has provided insights into strengths and limitations of the original approach to defining and quantifying cardiovascular health. The AHA

Chronotype was self‐reported at the UKB baseline visit (2006–2010) using a single validated question from the Morningness–Eveningness Questionnaire: “Do you consider yourself to be? Definitely a ‘morning’ person; More a ‘morning’ than ‘evening’ person; More an ‘evening’ than a ‘morning’ person; Definitely an ‘evening’ person; Do not know; Prefer not to answer. Age, ethnic background, sex, education, family history of CVD along with employment/shift work status were self‐reported at study baseline (2006–2010) using the touchscreen questionnaire.

They only looked at first myocardial infarction or stroke as incident CVD as these were “hard” diagnosis whereas heart failure or hospitalisation related to HF may be miscoded.

Results:

The mean baseline age of the study population was 57 years. Around 96% of participants identified as White, 47% were male, 37% held a college or university degree, and 58% had a family history of CVD.

Over a median 13.8 years of follow‐up, participants with a “definite evening” chronotype were associated with 79% higher prevalence of an overall poor LE8 score (<50 points) compared with “intermediate” type. The hazard ratio (HR) for total CVD was 1.03 (95% CI, 0.998–1.07) for the “definite morning” and 1.16 (95% CI, 1.10–1.22) for “definite evening” compared with “intermediate” chronotype (P‐trend: 0.10). LE8 only explained 75% of the association between evening chronotype and CVD (natural indirect effect comparing “definite evening” with “intermediate”: HR, 1.11 [95% CI, 1.09–1.13]).

Not unexpectedly, the definite evening chronotype was associated with a higher likelihood of poor scores in 6 of the 8 LE8 components compared with the “intermediate” group except for blood pressure and blood lipid components. The strongest associations were seen for nicotine exposure (prevalence ratio, 1.54 [95% CI, 1.50–1.58]) and inadequate sleep (prevalence ratio, 1.42 [95% CI, 1.36–1.48]). Associations between chronotype and overall LE8 score were stronger among female compared with male participants.

Since the definite evening chronotype had poorer LE8 scores, they are likely to have worse incident cases of CVD, Indeed, compared with participants with an “intermediate” chronotype, those with a “definitely evening” chronotype had a 16% higher risk of CVD (HR, 1.16 [95% CI, 1.10–1.22]), whereas participants reporting “definitely morning” chronotypes were not at higher risk (HR, 1.03 [95% CI, 0.99–1.07]) after adjustment for age, ethnic background, sex, Townsend deprivation index, education, family history of CVD, and employment/shift work status.

It would seem that most of this association was explained by a poor overall LE8 score, with nicotine exposure being the strongest individual mediator. No natural direct effect of chronotype on CVD was observed. Individuals with extreme chronotypes may experience irregularity of various behaviours relevant to cardiovascular health such as irregular eating schedules, lower levels of physical activity, and inadequate or irregular sleep, some of which further exacerbate the misalignment. 

Summary

It would be nice if all of us work on a 9-5 work schedule but some of our patients may not have that choice. We now have a set of modifiable risk factors which we can mitigate including nicotine exposure, diet, physical activity, BP, blood glucose and blood lipids in these patients. We need to strive for adequate sleep in these patients. The evening chronotype should be considered a CV risk enhancers in our CV risk assessment.

References:

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  2. Kianersi S, Liu Y, Guasch‐Ferre M, Redline S, Schernhammer E, Sun Q, Huang T. Chronotype, unhealthy lifestyle, and diabetes risk in middle‐aged U.S. women: a prospective cohort study. Ann Intern Med. 2023;176:1330–1339
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  17. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001078. Accessed 23/2/2026