People who stay up late may face higher cardiovascular risk. However, this large UK study shows that healthier sleep, smoking habits, and metabolic control could offset much of that danger.
Study: Chronotype, Life’s Essential 8, and Risk of Cardiovascular Disease: A Prospective Cohort Study in UK Biobank. Image Credit: PeopleImages / Shutterstock.com
A recent study published in the Journal of the American Heart Association (JAHA) explores the association between an individual’s chronotype and incident myocardial infarction or stroke, key indicators of cardiovascular disease risk.
Circadian rhythms may determine cardiovascular health
Cardiovascular disease (CVD) remains the leading cause of death worldwide. Although various lifestyle factors like diet, physical activity, and nicotine use can be modified to reduce the risk of CVD, recent guidelines by the American Heart Association (AHA) emphasize the importance of sleep duration for maintaining optimal cardiovascular health.
An individual’s chronotype can vary based on their sleep-wake timing, with certain circadian rhythms associated with a greater risk of cardiometabolic disease. For example, adults with an evening chronotype are more likely to experience circadian dysfunction than those with an intermediate chronotype.
Circadian misalignment can negatively impact behavior and reward-related brain functions, which have been implicated in the development of unhealthy lifestyle behaviors like poor diet quality, alcohol intake, and smoking. Chronic disruption in normal circadian cycles also leads to a wide range of physiological effects, including increased activation of the nervous system, dysregulation of blood pressure, glucose, and lipid profiles, as well as altered hypothalamic-pituitary-adrenal (HPA) axis activity.
UK Biobank data link chronotype, LE8, and CVD
The researchers of the current study used data from the participants of the United Kingdom Biobank between 39 and 74 years of age who had no prior history of myocardial infarction or stroke. Chronotype was self-reported using a single question, whereas cardiovascular health was assessed using the Life’s Essential 8 (LE8) score.
Cox proportional hazards models were used to evaluate the association between chronotype and CVD risk over time. These estimates were adjusted for various sociodemographic, occupational, and familial risk factors.
LE8 effects were further categorized as LE8-independent direct and LE8-mediated indirect natural effects.
Evening chronotypes show higher CVD risk via lifestyle
Study participants were monitored for a median of 13.8 years, with 17,584 new CVD events reported during this period, defined as first-onset myocardial infarction or stroke, 7,214 of which were strokes and 11,091 heart attacks. The mean LE8 score was 67, with median scores of 70 and 65 for women and men, respectively. Unfavorable scores of less than 50 were reported in 7 % of the study cohort.
About 67 % of study participants reported an intermediate chronotype, whereas 8 % had a ‘definitely evening’ chronotype. As compared to the intermediate chronotype, those with a ‘definitely evening’ chronotype were more likely to be younger, deprived, educated, and shift workers.
Whereas study participants with an intermediate chronotype had a mean LE8 score of 68, those with a ‘definitely evening’ chronotype had a mean LE8 score of 65. Poor LE8 scores were approximately 79 % more common among participants with the ‘definitely evening’ chronotype than among those with the intermediate chronotype, and the prevalence of low LE8 scores was approximately 5 % lower among participants with the ‘definitely morning’ chronotype.
Poor LE8 scores were more common in six out of eight LE8 components with the ‘definitely evening’ chronotype. The exceptions to these observations included blood pressure and blood lipids, whereas nicotine use and insufficient sleep showed the strongest associations with poor LE8 scores.
Among study participants with the ‘definitely morning’ chronotype, poor sleep was about 30 % more likely, whereas poor diet was less common. Women with the ‘definitely evening’ chronotype were nearly twice as likely (96 % higher) to have low LE8 scores, whereas the prevalence of low LE8 scores among men was about 67 % higher.
CVD risk increased by 16 % among participants with the evening chronotype, with suggestively stronger but not statistically significant associations observed among older individuals, men, non-shift workers, and those with low LE8 scores. No evidence of effect modification by cardiovascular genetic risk was observed.
The natural indirect effect of the LE8 score accounted for about 75 % of the association between chronotype and CVD. Nicotine use mediated the greatest risk at 34 % of the association, whereas sleep, blood glucose levels, body weight, and diet contributed 11–14 % each to CVD risk.
Long follow-up strengthens findings but limits causality claims
This study is the first to explore the role of LE8 in mediating chronotype-incident CVD associations. Additional strengths include its prospective design that supports temporal ordering but does not establish causality, a long follow-up period, and the inclusion of multiple health behaviors.
The large sample size provided greater statistical power while reducing random error, with multiple sensitivity analyses performed to ensure the robustness of any observations.
Notable limitations include the use of a single chronotype question, which could allow for misclassification. Nevertheless, the responses to this question strongly correlated with validated scores.
The single-point chronotype and LE8 score assessments limit certainty that chronotype preceded cardiovascular health behaviors, reducing confidence in the temporal sequence of mediators and outcome. Additionally, the mostly White and healthy composition of the U.K. Biobank cohort limits the generalizability of these findings.
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