Is going to bed after midnight bad? Brehan Crawford, L.Ac., with the Chinese medicine circadian organ clock chart

Is Going to Bed After Midnight Bad?

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    Most sleep advice is about how many hours you get. The more useful question is which hours. A large study that tracked sleep with wrist sensors found more heart disease in people who fell asleep after midnight, and Chinese medicine has said something similar for a very long time. Here is what the research shows, what your body is doing between 11 pm and 3 am, and how to move your bedtime.

    The short answer

    For your heart, yes. In a UK Biobank study, falling asleep at midnight or later was linked to a 25 percent higher risk of cardiovascular disease than falling asleep between 10 and 11 pm, even after sleep duration was accounted for. Your body runs its cleanup on a schedule, and in Chinese medicine the hours from 11 pm to 3 am belong to the Gallbladder and the Liver. Eight hours at the wrong time does not fully replace them. Turn your lights off around 10 pm.

    The short version, on video.

    Is going to bed after midnight bad?

    For your heart, the evidence says yes. The study I talk about in the video was published in the European Heart Journal – Digital Health in 2021. The researchers used seven days of wrist accelerometer recordings, collected from 103,712 UK Biobank participants, to work out when each person actually fell asleep, not when they remembered going to bed. Over an average follow-up of 5.7 years, 3,172 cases of cardiovascular disease were recorded.[1]

    Falling asleep between 10:00 and 10:59 pm carried the lowest risk. Compared with that hour, falling asleep at midnight or later was linked to a 25 percent higher risk, and falling asleep between 11:00 and 11:59 pm to a 12 percent higher risk. Those figures come from the model that accounted for sleep duration, sleep irregularity and the established cardiovascular risk factors.[1]

    The PURE study followed 112,198 people in 21 countries for 9.2 years. Those who usually went to bed after midnight had a 10 percent higher risk of death, heart attack, stroke or heart failure than those who went to bed between 10 pm and midnight, after full adjustment.[2] In the Sleep Heart Health Study, 4,765 adults were followed for an average of 11 years. Those with weekday bedtimes after midnight had a 56 percent higher risk of developing congestive heart failure than those in bed between 10 and 11 pm.[3]

    These are observational studies, and the pattern repeats across all three: the hearts that do best belong to people who are asleep before midnight. Sleep, meals and mood sit inside one daily rhythm. I covered the meal side in Is It Better to Eat Earlier in the Day?, and learning to live inside that rhythm is the work we do in Gut Brain Synchrony.

    What is the best time to go to bed for adults?

    Around 10 pm. In the UK Biobank data, the sweet spot for falling asleep was 10:00 to 10:59 pm.[1] Nobody falls asleep the second the lamp goes off, so if you want to be asleep inside that hour, turn your lights off around 10.

    Earlier was not better. People who fell asleep before 10 pm had a 24 percent higher risk than the 10 o’clock group, and the PURE study found the same U shape, with bedtimes before 10 pm carrying a 9 percent higher risk.[1][2] The UK researchers also found that the link was stronger in women. In men, only the before-10 group reached statistical significance.[1]

    Chinese medicine arrives at the same hour by a different road. The traditional teaching is to be asleep before the Zi hour begins at 11 pm, so that you are already at rest when the night’s work starts.

    Does it matter what time you go to bed as long as you get 8 hours of sleep?

    Yes. Sleeping eight full hours is good, but it does not fully fix this if you are off track. Sleep from 4 am to noon and you still miss the 11 to 3 window, no matter how many hours you clock. The bedtime study says the same thing in its own language: the after-midnight risk was still there once sleep duration was accounted for.[1]

    What a mistimed night does to blood pressure

    Researchers at Brigham and Women’s Hospital had healthy adults live for three days on a schedule flipped by 12 hours, sleeping in the day and awake at night. Their 24-hour blood pressure rose by 3.0 mmHg systolic and 1.5 mmHg diastolic. The largest change came during sleep, where systolic pressure ran 5.6 mmHg higher. Inflammatory markers, C-reactive protein among them, rose by 3 to 29 percent.[4]

    Sleep is when your blood pressure is meant to come down. Put the sleep on the wrong side of the clock and it does not come down as far.

    Stretch that over a working life and it shows. In the Nurses’ Health Studies, which followed 189,158 women for 24 years, more years of rotating night shifts meant a higher risk of coronary heart disease. The increase was small in absolute terms, and it faded after the nurses stopped working nights.[5]

    Regular matters as much as long

    Timing also means consistency. Among 60,977 UK Biobank participants, the more regular sleepers had a 20 to 48 percent lower risk of dying from any cause than the least regular fifth, and a 22 to 57 percent lower risk of dying from cardiometabolic disease. Regularity predicted mortality better than sleep duration did.[6]

    In the Multi-Ethnic Study of Atherosclerosis, 1,992 adults wore a wrist monitor for seven days. Those whose time of falling asleep varied by more than 90 minutes from night to night had about twice the risk of a cardiovascular event of those who stayed within 30 minutes.[7]

    The right hours, and the same hours.

    What does the Chinese medicine body clock say about 11 pm to 3 am?

    That your body runs cleanup on a schedule. In Chinese medicine we call this the organ clock. Qi makes one full circuit of the twelve organ systems every day and night, cresting in each for about two hours. Acupuncturists wrote the idea down as a formal system many centuries ago under the name zi wu liu zhu, the midnight-noon ebb and flow.

    01 11 pm to 1 am, the Gallbladder. This is the Zi hour, the deepest point of yin and the moment the next day’s yang is born. The Gallbladder clocks in to clear out the day’s toxins. The Inner Classic says the other eleven organs all take their lead from the Gallbladder, which is why this hour sets up everything that follows.
    02 1 am to 3 am, the Liver. The Liver takes over the shift. The Inner Classic puts it plainly: when a person lies down, the blood returns to the Liver. That stored blood is how the Liver restores itself, and it only happens when you are lying down and at rest.
    03 11 am to 1 pm, the Heart. The Heart sits directly across the clock from the Gallbladder, noon to its midnight. A Ming dynasty text, the Yixue Rumen (Introduction to Medicine), states that the Heart and the Gallbladder communicate. In the Chinese medicine view, what you do with the Gallbladder hour shows up in the Heart.

    So if you are still awake at 2 am, scrolling or working or stressing, the two organs on the night shift never get to do their work. Whatever they did not clear stays in your system another day. This builds up.

    What modern research sees in the same hours

    Physiology does not use the words Gallbladder and Liver the way the classics do, but it has found the same principle: clearance and repair are timed. In mice, sleep opens the fluid spaces of the brain by about 60 percent and speeds the removal of metabolic waste such as beta-amyloid.[8] That flow is not only a matter of being asleep. It follows its own circadian rhythm and peaks in the middle of the animal’s normal rest phase.[9]

    The liver keeps a clock too. A review in Chemical Research in Toxicology describes all three phases of the liver’s detoxification machinery as being under strong circadian regulation, and lists jet lag and shift work among the things that disturb it.[10] In humans, when researchers drew blood every 90 minutes from eight volunteers, the marker of cholesterol synthesis peaked at night, between midnight and 4 am.[11]

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    How to go to bed earlier

    You cannot force sleep. You can set up the conditions for it. Light is the strongest signal your clock receives, so start there.

    01 Get outside in the morning. When volunteers in a University of Colorado study went camping with nothing but natural light, their internal clocks moved earlier and lined up with the sun, with the biological night beginning at sunset. The latest sleepers shifted the most.[12]
    02 Dim the house after sunset and put the screen down. In a controlled comparison, people who read on a light-emitting e-reader before bed took longer to fall asleep, made less melatonin, pushed their clock later and were less alert the next morning than when they read a printed book.[13]
    03 Sleep in the dark. Among 88,905 people who wore wrist light sensors for a week, those with the brightest nights went on to have a 47 percent higher risk of heart attack and a 56 percent higher risk of heart failure than those with dark nights.[14] In the lab, a single night of sleeping in moderate room light raised heart rate during sleep and increased insulin resistance the next morning.[15]
    04 Warm up, then let yourself cool. A warm bath or shower at 104 to 108.5°F (40 to 42.5°C), taken one to two hours before bed for as little as ten minutes, shortened the time it took to fall asleep in a meta-analysis drawn from 17 studies.[16]
    05 Move in small steps, then hold the time. Bring your bedtime forward a little every few nights until lights out lands at 10. Then keep it there, weekends included.

    Finish dinner early as well. For the gut side of sleep, read Gut Health Basics: Your Sleep.

    Bedtime questions, answered

    Is midnight too late to go to bed?

    By these numbers, yes. Going to bed after midnight carried a higher risk in all three bedtime studies. You do not have to fix it in one night, and partway counts: in the UK Biobank data, the 11 o’clock hour carried about half the added risk of the after-midnight group.[1]

    How do I go to bed early when I am a night owl?

    Start with morning light. In the camping study, the later chronotypes moved the most.[12] It is worth the effort. Among 433,268 UK Biobank adults followed for an average of six and a half years, definite evening types had a 10 percent higher risk of dying from any cause than definite morning types.[17]

    Why do I wake up at 3 am, according to Chinese medicine?

    On the organ clock, 1 to 3 am belongs to the Liver and 3 to 5 am to the Lung. Waking at the same time night after night is read as the organ on that shift asking for attention. With the Liver hours, we look at stress, late meals and how well the blood is nourished. If sleep itself is the struggle, start with For People Who Cannot Sleep.

    If you want your heart to be happy, hit the sweet spot. Lights off around 10.

    — Brehan Crawford, L.Ac.

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    References

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    2. Wang C, Hu B, Rangarajan S, et al. Association of bedtime with mortality and major cardiovascular events: an analysis of 112,198 individuals from 21 countries in the PURE study. Sleep Med. 2021;80:265-272. doi:10.1016/j.sleep.2021.01.057
    3. Yan B, Li R, Li J, et al. Sleep Timing May Predict Congestive Heart Failure: A Community-Based Cohort Study. J Am Heart Assoc. 2021;10(6):e018385. doi:10.1161/JAHA.120.018385
    4. Morris CJ, Purvis TE, Hu K, Scheer FAJL. Circadian misalignment increases cardiovascular disease risk factors in humans. Proc Natl Acad Sci U S A. 2016;113(10):E1402-E1411. doi:10.1073/pnas.1516953113
    5. Vetter C, Devore EE, Wegrzyn LR, et al. Association Between Rotating Night Shift Work and Risk of Coronary Heart Disease Among Women. JAMA. 2016;315(16):1726-1734. doi:10.1001/jama.2016.4454
    6. Windred DP, Burns AC, Lane JM, et al. Sleep regularity is a stronger predictor of mortality risk than sleep duration: A prospective cohort study. Sleep. 2024;47(1):zsad253. doi:10.1093/sleep/zsad253
    7. 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. doi:10.1016/j.jacc.2019.12.054
    8. Xie L, Kang H, Xu Q, et al. Sleep drives metabolite clearance from the adult brain. Science. 2013;342(6156):373-377. doi:10.1126/science.1241224
    9. Hablitz LM, Plá V, Giannetto M, et al. Circadian control of brain glymphatic and lymphatic fluid flow. Nat Commun. 2020;11(1):4411. doi:10.1038/s41467-020-18115-2
    10. Zmrzljak UP, Rozman D. Circadian regulation of the hepatic endobiotic and xenobitoic detoxification pathways: the time matters. Chem Res Toxicol. 2012;25(4):811-824. doi:10.1021/tx200538r
    11. Gälman C, Angelin B, Rudling M. Bile acid synthesis in humans has a rapid diurnal variation that is asynchronous with cholesterol synthesis. Gastroenterology. 2005;129(5):1445-1453. doi:10.1053/j.gastro.2005.09.009
    12. Wright KP, McHill AW, Birks BR, Griffin BR, Rusterholz T, Chinoy ED. Entrainment of the human circadian clock to the natural light-dark cycle. Curr Biol. 2013;23(16):1554-1558. doi:10.1016/j.cub.2013.06.039
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    14. Windred DP, Burns AC, Rutter MK, et al. Light Exposure at Night and Cardiovascular Disease Incidence. JAMA Netw Open. 2025;8(10):e2539031. doi:10.1001/jamanetworkopen.2025.39031
    15. Mason IC, Grimaldi D, Reid KJ, et al. Light exposure during sleep impairs cardiometabolic function. Proc Natl Acad Sci U S A. 2022;119(12):e2113290119. doi:10.1073/pnas.2113290119
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