Sleeping at this time every day can really reduce the risk of cardiovascular disease! Try it now!

Some people say that going to bed early and getting up early is good for your health. Others say that as long as you don't feel uncomfortable, going to bed late and getting up late is just as good as going to bed early and getting up early. Which statement is correct? Is there an optimal time to fall asleep?

In recent years, many studies have shown that going to bed between 10 and 11 p.m. is best for cardiovascular health. This conclusion has attracted widespread attention and discussion.

Going to bed between 10pm and 11pm is best for your cardiovascular system

In November 2021, researchers from the University of Oxford and the University of Exeter in the UK published a research paper titled "Accelerometer-derived sleep onset and cardiovascular disease incidence: a UK Biobank cohort study" in the European Heart Journal-Digital Health, a journal of the European Society of Cardiology.

A total of 88,026 British subjects were included in this study, including 51,214 women (58.2%) and 36,812 men (41.8%), with an average age of 61.43 years. The researchers collected data on the start time of sleep and wake time of these subjects through wristband accelerometers, and also collected a series of information on age, gender, regularity of sleep, self-reported sleep time type, smoking status, body mass index BMI, and the presence of chronic diseases such as diabetes/hypertension.

Then, the researchers followed them up for an average of 5.7 years and found that 3,172 (3.58%) subjects developed cardiovascular diseases, including myocardial infarction, heart failure, chronic ischemic heart disease, stroke and transient ischemic attack. Among these patients with cardiovascular diseases, 43% went to bed in the early morning and later, 38% went to bed between 11 and 12 pm, and only 15% went to bed between 10 and 11 pm, and 4% went to bed before 10 pm.

After eliminating confounding factors, the researchers concluded:

The time of falling asleep and the risk of cardiovascular disease show a "U"-shaped relationship. Going to bed at 10-11 pm has the lowest risk of cardiovascular disease, going to bed too early or too late will increase the risk, and going to bed in the early morning (12 o'clock) or later has the highest risk.

Compared with those who fall asleep between 22:00 and 22:59:

Falling asleep before 22:00 increases the risk of cardiovascular disease by 24%;

Falling asleep between 23:00 and 23:59 increases the risk of cardiovascular disease by 12%;

Falling asleep at midnight or later increases the risk of cardiovascular disease by 25%;

In further analysis by sex, the researchers found that the association with increased cardiovascular risk was stronger in women, but the reason for this was unclear.

The researchers speculate that this may be due to gender differences in the endocrine system's response to circadian rhythm disruption; in addition, the older age of the subjects is also a confounding factor, because the cardiovascular risk of postmenopausal women is increased, so it is also possible that there is no gender difference in the association between bedtime and cardiovascular disease.

This is one of the most in-depth studies to date on the relationship between sleep and cardiovascular disease risk.

Of course, no study can be perfect. This study also has its limitations, such as the subjects were mainly white people with relatively good socioeconomic backgrounds, the average age of the participants was older, and the risk of cardiovascular disease in postmenopausal women would increase. It is indeed not representative of the entire population, and it cannot be concluded that there is a causal relationship.

Image source: pixabay

It should be pointed out that my country has a vast territory, spanning five time zones from east to west, but all parts of my country uniformly adopt Beijing time in the East Eighth Zone. Therefore, the 22:00 to 23:00 of Beijing, located in the East Eighth Zone, and Urumqi, located in the East Sixth Zone, are not the same concept. The sunset time in Beijing is early, and the sunset time in Urumqi is delayed by 2 hours. So if the biological clock of Beijingers is 22:00 to 23:00, then for the biological clock of Urumqi people, the best time to fall asleep should be adjusted to 0:00 to 1:00. People living in other time zones in my country can also refer to this rule to convert the best time to fall asleep.

Sleeping 6 to 9 hours a night is best for your heart

Scientists have long believed that there is a link between sleep and heart health, but because there are many factors that affect both heart health and sleep, it makes it more difficult to determine cause and effect. Many scientific studies on this are observational, that is, observing different groups of people to see who will get sick. On September 2, 2019, the Journal of The American College of Cardiology published a study of nearly 500,000 people from the University of Colorado Boulder. Unlike previous observational studies, this study also used genetic research.

Using Mendelian randomization, the researchers found 27 genetic variants associated with short sleep, a risk factor for myocardial infarction. The researchers also considered 30 factors, including weight, physical activity, socioeconomic status, and mental health, and concluded that sleep duration itself (rather than other factors) is a potential causal factor affecting myocardial infarction risk.

The findings suggest that even if you don't smoke, exercise regularly and have no genetic predisposition to cardiovascular disease, simply not getting enough sleep or sleeping too much can increase your risk of heart disease.

Compared with those who slept 6 to 9 hours a night, those who slept less than 6 hours a night had a 20% higher risk of having a heart attack during the study period. But sleeping too long is not good either, with those who slept more than 9 hours a night having a 34% higher risk of having a heart attack during the study period.

And people who sleep too much have an even higher risk than those who don't get enough sleep! The further away from the range of 6 to 9 hours of sleep per night, the higher the risk of myocardial infarction. For example, compared with those who sleep 7 to 8 hours a night, those who sleep 5 hours a night have a 52% increased risk of myocardial infarction, and those who sleep 10 hours have a two-fold increased risk of myocardial infarction.

So what is the optimal sleep duration? Researchers believe that 6 to 9 hours of sleep per night is the most beneficial sleep duration for heart health.

When the researchers looked at people with a genetic predisposition to heart disease separately, they found that these people could reduce their risk of heart attack by 18% if they slept 6 to 9 hours a night. "This is encouraging news," said Iyas Daghlas, a professor at Harvard Medical School and the lead author of the paper. "Regardless of your genetic risk for heart attack, a healthy amount of sleep may reduce your risk of heart attack, just as a healthy diet, not smoking, and other lifestyle factors may do."

But this study did not explore why too short or too long sleep increases the risk of heart attack. According to some previous research conclusions, we know that too little sleep affects the inner wall of the arteries or endothelial cells, affects the bone marrow development of inflammatory cells, and also leads to poor diet and eating at inappropriate times. These consequences will affect body weight and thus heart health. Too much sleep may also promote inflammatory response in the body, and inflammation is also related to cardiovascular disease.

Other studies linking sleep to heart health

On September 15, 2023, a randomized cross-over design trial conducted by a research team from Columbia University showed that sleeping 1.5 hours less per day for 6 consecutive weeks significantly impaired the ability of the endothelial to clear oxidative stress; over time, the continuous accumulation of endothelial oxidative stress will increase the risk of cardiovascular disease.

On September 3, 2021, a large cohort study involving more than 320,000 adult participants was published in JAM Network Open, revealing the "relationship between sleep time and mortality in East Asian populations." The results showed that there was a J-shaped correlation between sleep time and all-cause mortality-7 hours of sleep was the lowest point associated with death from all causes, cardiovascular disease and other causes. Among men, compared with 7 hours of sleep, sleeping more than this value per night, such as 8, 9, and 10 hours, will increase the all-cause mortality rate by 9%, 18%, and 43%, respectively; and sleeping less than 5 hours, the all-cause mortality rate of participants will also increase by 16%. Similarly, among women, compared with 7 hours of sleep per night, sleeping 1 hour more or 1 hour less will increase the all-cause mortality rate.

On April 28, 2022, a research team from Fudan University published a study in a Nature journal, which found that the optimal sleep duration is 7 hours, which is beneficially associated with cognitive function and mental health; however, when the sleep duration is less than or more than 7 hours, it is associated with decreased cognitive function and poorer mental health.

These studies on the link between sleep and heart health continue to remind us:

You should go to bed when it is time to sleep. Not sleeping when you should or not getting enough sleep are both going against your health.

In order to ensure good sleep quality, if conditions permit, try to fall asleep between 22:00 and 23:00, and try to sleep for 6 to 9 hours, 7 hours is best!

References

[1]ShahramNikbakhtian,AngusBReed,BernardDillonObika,DavideMorelli,AdamCCunningham,MertAral,DavidPlans,Accelerometer-derivesleeponsettimingandcardiovasculardiseaseincidence:aUKBiobankcohortstudy,EuropeanHea rtJournal-DigitalHealth,2021;,ztab088,https://doi.org/10.1093/ehjdh/ztab088CelineVetteretal.SleepDurat ionandMyocardialInfarction.JournaloftheAmericanCollegeofCardiology(2019).DOI: 10.1016/j.jacc.2019.07.022

[2]Shah,R.,Shah,VK,Emin,M.etal.Mildsleeprestrictionincreasesendothelialoxidativestressinfemalepersons.SciRep13,15360(2023).https://doi.org/10.1038/s41598-023-42758-y

[3]SvenssonT,SaitoE,SvenssonAK,etal.AssociationofSleepDurationWithAll-andMajor-CauseMortalityAmongAdultsinJapan,China,Singapore,andKorea.JAMANetwOpen.2021;4(9):e2122837.doi:10.1001/jamanetworkopen.2021.22837

[4]LiY,SahakianBJ,KangJ,LangleyC,ZhangW,XieC,XiangS,YuJ,ChengW,FengJ.Thebrainstructureandgeneticmechanismsunderlyingthenonlinearassociationbetweensleepdura tion,cognitionandmentalhealth.NatAging.2022May;2(5):425-437.doi:10.1038/s43587-022-00210-2.Epub2022Apr28.Erratumin:NatAging.2022May;2(5):453.PMID:37118065.

Author: Zeng Xinyue, a popular science writer

Reviewer: Tang Qin, Director and Researcher of the Science Popularization Department of the Chinese Medical Association