Evening Chronotype and the Heart: 16% Higher Cardiovascular Disease Risk

What is chronotype and social jetlag?

Chronotype is the individual temporal setting of the biological clock: when exactly the body schedules wake-up, peak alertness, and sleep onset. It is roughly 50% genetically determined; the rest is shaped by age, light exposure, and established routine. Early birds fall asleep and wake up earlier; night owls do so later; most people occupy an intermediate position.

The problem for night owls in modern society is social jetlag: a daily mismatch between biological time and the time imposed by work schedules. A person with an evening chronotype is forced to wake up 2–3 hours earlier than their internal clock requires — like flying across several time zones every week, repeatedly.

How much higher is the cardiovascular disease risk for night owls?

Kianersi et al. (Journal of the American Heart Association, 2026) analyzed data from 322,777 participants in UK Biobank aged 39–74 with no cardiovascular disease at baseline. Chronotype was assessed using a standard self-report question: participants classified themselves as "definitely morning," "more morning," intermediate, "more evening," or "definitely evening."

Sample distribution: 24% definitely morning, 67% intermediate, 8% definitely evening. The intermediate chronotype served as the reference group. Results after multivariable adjustment:

• Definitely morning vs. intermediate: HR = 1.03 (95% CI: 0.998–1.07) — not significant.
• Definitely evening vs. intermediate: HR = 1.16 (95% CI: 1.10–1.22) — significantly higher cardiovascular disease risk.

The 8% of participants with an evening chronotype carried a 16% higher relative risk of cardiovascular events. The association persisted after adjustment for age, sex, ethnicity, smoking, BMI, physical activity, and socioeconomic status.

What do long-term follow-up data show?

Hublin C. and Kaprio J. (Chronobiology International, 2023) followed 23,854 participants in the Finnish Twin Cohort for 37 years, during which 8,728 deaths were recorded. This is one of the longest prospective studies on chronotype and mortality.

In the adjusted model, an evening chronotype was associated with HR = 1.09 (95% CI: 1.01–1.18) for all-cause mortality. However, when the analysis was restricted to participants who did not smoke and consumed alcohol moderately or not at all, the association disappeared. The authors concluded that a substantial portion of the excess risk associated with an evening chronotype is mediated by behavioral factors — primarily smoking and excessive alcohol use — rather than by the biological chronotype itself.

What happens in the metabolism of night owls?

Toffol et al. (European Psychiatry, 2025) analyzed plasma metabolomics data from approximately 245,000 UK Biobank participants. Compared to the morning chronotype, the evening chronotype showed higher levels of glycoprotein acetyls — a systemic marker of inflammation — as well as higher triglycerides and VLDL lipid content; HDL levels were lower. These changes were partially but not fully explained by sociodemographic and behavioral factors.

The proposed mechanism is circadian misalignment: when a night owl wakes up on a social schedule earlier than their biological time, cortisol has not yet reached its morning peak and melatonin has not yet declined. Chronic misalignment disrupts the physiological sequence of hormonal and metabolic events: insulin sensitivity decreases, the inflammatory background rises, and evening eating behavior shifts.

Limitations: what is not established here

All studies mentioned are observational. Chronotype was determined primarily by self-report rather than by objective chronobiological measurement. Residual confounding is probable: evening chronotype correlates with a range of behavioral and social factors. None of the studies tested whether forcing a chronotype shift toward morning actually improves cardiovascular outcomes.