If you fly across time zones regularly, you should know that circadian disruption is not just an inconvenience. Circadian disruption is increasingly linked to cardiovascular risk — although the evidence comes mainly from studies of irregular sleep and shift work, not from frequent flyers themselves.

What happens when your clock breaks

Your body runs on a 24-hour internal clock — the circadian rhythm — that regulates nearly every physiological process: hormone release, blood pressure patterns, heart rate variability, glucose metabolism, immune function, and inflammatory responses. When you cross time zones, this clock doesn't reset instantly. As a rough rule of thumb, it takes about one day per time zone to fully adjust.

A flight from New York to Central Europe crosses six time zones. That can mean up to a week of circadian misalignment. During that time, your cortisol rhythm is out of step with local time. Laboratory studies of circadian misalignment show that blood pressure may not dip at night the way it should (a pattern called "non-dipping" that's independently associated with cardiovascular events), glucose regulation is impaired, and inflammatory markers rise. Direct measurements in travellers are still scarce.

For a single trip, this is temporary and recoverable. For people who fly transatlantically every month or two, the cumulative effect may be a chronic low-grade circadian disruption that doesn't fully resolve between trips.

The evidence

A large study of more than 72,000 UK Biobank participants, whose sleep was measured with wrist-worn accelerometers, found that the most irregular sleepers — irregular sleep being a proxy for circadian disruption — had a 26% higher risk of major cardiovascular events over eight years than regular sleepers. Getting the recommended amount of sleep did not offset this excess risk. A smaller US study (MESA) found about twice the risk of cardiovascular events in older adults with the most irregular sleep.

Shift work represents the most extreme form of chronic circadian disruption. A meta-analysis of 21 studies found about 17% higher cardiovascular risk in shift workers, with the excess appearing mainly after five or more years of exposure; in the large Nurses' Health Studies, ten or more years of rotating night shifts were linked to roughly 15–18% higher risk of coronary heart disease. No study has directly measured cardiovascular outcomes in frequent flyers. While frequent business travel isn't shift work, the mechanism is thought to be similar: repeated forced misalignment between your internal clock and the external environment.

The blind spot in risk assessment

Most cardiovascular risk calculators don't account for circadian disruption. SCORE2 doesn't ask how often you fly. Jet lag rarely features in a routine risk assessment. But the biological effects — elevated cortisol, impaired glucose regulation, inflammatory activation — show up in standard biomarkers that are measured in any thorough check-up. The question is whether anyone connects the dots.

What you can do

You probably can't stop flying. But you can manage the impact:

  • Pre-adjust your schedule: Shift your sleep and meal times toward the destination time zone 2–3 days before departure. Even a 1–2 hour shift helps.
  • Light exposure timing: Bright light in the morning (destination time) accelerates clock resetting. Avoid bright light at the wrong time — this is the single most powerful tool for circadian adjustment.
  • Melatonin: Melatonin taken close to destination bedtime for a few days can reduce jet lag, according to a Cochrane review, especially after eastward flights across five or more time zones. Doses between 0.5 and 5 mg were similarly effective (5 mg helped people fall asleep slightly faster); doses above 5 mg appear to be no more effective. Taken at the wrong time of day, it can delay adaptation.
  • Protect sleep architecture: Alcohol disrupts REM sleep. Caffeine stays in the body for many hours. Both are standard coping mechanisms for jet lag, and both make it worse.
  • Plan your first day wisely: Avoid scheduling important tests or demanding commitments right after arrival. Morning daylight and moderate physical activity on the first day help reset your rhythm, and a lighter day before demanding commitments gives the clock time to adjust. Fasting blood tests are often easiest early in the morning after arrival, when appetite is suppressed anyway.

What this means for your check-up

Several routine markers are directly affected by chronic circadian disruption: hs-CRP (inflammation), fasting glucose and HOMA-IR (glucose dysregulation), cortisol patterns (when clinically indicated), and blood pressure. Sleep is often disrupted in frequent flyers; if it is persistently poor, a screening questionnaire such as STOP-Bang can help check for obstructive sleep apnoea, a common and treatable cardiovascular risk factor.

These results are best interpreted in the context of your travel pattern — a slightly elevated hs-CRP in someone who flies transatlantically every three weeks means something different than the same number in someone who stays put. If you travel frequently across time zones, it is worth telling your doctor how often, so that this context is part of your risk assessment.

References

  1. Chaput JP, et al. Sleep regularity and major adverse cardiovascular events: a device-based prospective study in 72 269 UK adults. J Epidemiol Community Health. 2025;79(4):257. doi:10.1136/jech-2024-222795
  2. Huang T, Mariani S, Redline S. Sleep irregularity and risk of cardiovascular events: the Multi-Ethnic Study of Atherosclerosis. J Am Coll Cardiol. 2020;75(9):991-999.
  3. Torquati L, et al. Shift work and the risk of cardiovascular disease. A systematic review and meta-analysis including dose-response relationship. Scand J Work Environ Health. 2018;44(3):229-238.
  4. Vetter C, et al. Association between rotating night shift work and risk of coronary heart disease among women. JAMA. 2016;315(16):1726-1734.
  5. Knutson KL, Reutrakul S. Consequences of circadian disruption on cardiometabolic health. Sleep Med Clin. 2015;10(4):455-468.
  6. Herxheimer A, Petrie KJ. Melatonin for the prevention and treatment of jet lag. Cochrane Database Syst Rev. 2002;(2):CD001520.
Prof. Dr. med. Markus Guba

Head of Liver Surgery and Transplantation at LMU University Hospital Munich. Edits this independent journal in a private capacity; views are his own. About →

This article is general information and not individual medical advice. Decisions about tests and treatment belong in a conversation with your own physician.