Is there a sweet spot for the time of day you go to sleep?
When we get our seven to eight hours of sleep a day, it certainly doesn’t matter whether we go to bed just after dinner or at two in the morning.
Well, a new study says that does matter – and concludes that the amount of time you go to sleep is linked to your risk for heart disease.
The sweet spot for falling asleep is between 10 p.m. and 11 p.m.
Doing this later – or sooner – increases your risk of having a heart attack, heart failure, chronic ischemic heart disease, stroke, and transient ischemic attack.
The University of Exeter study does not explain the mechanism behind these results, other than a disturbance in our internal clock.
The results are fascinating and add another piece to the puzzle of how sleep affects our health.
What happened in the study?
This was a quality study that objectively measured when participants went to sleep and when they woke up.
This meant that the data were of higher quality than studies that relied on participant self-reporting.
It was also a large study of 88,026 people recruited between 2006 and 2010.
Participants were part of the UK Biobank, which tracked the health data of 500,000 people over four years and shared the data with scientists around the world.
The mean age was 61 years (range 43 to 79 years) and 58 percent were women.
Onset of sleep and wake-up time data were collected over seven days using a wrist-worn accelerometer.
Participants completed demographic, lifestyle, health, and physical exams and questionnaires.
They were then followed up for an average of 5.7 years, during which time 3,172 participants (3.6 percent) developed cardiovascular disease.
The results showed that women are at higher risk
Heart disease was highest in those who slept at midnight or later – and lowest in those who fell asleep between 10:00 PM and 10:59 PM.
The researchers analyzed the relationship between falling asleep and cardiovascular events after adjusting to age, gender, sleep duration, sleep irregularity (defined as different times of falling asleep and waking up), self-reported chronotype (early bird or night owl), smoking status, body mass index, Diabetes, blood pressure, blood cholesterol, and socioeconomic status.
Compared to those who fell asleep during the sweet spot, there are:
- 25 percent higher risk of cardiovascular disease if you fall asleep at midnight or later
- 12 percent higher risk for 11:00 PM to 11:59 PM
- 24 percent higher risk for those who fall asleep before 22 O `clock.
The association with an increased cardiovascular risk was stronger in women.
Study author Dr. David Plans said, “Our study shows that the optimal time to fall asleep is at a certain point in the body’s 24-hour cycle, and deviations can be harmful to your health.
“The riskiest time was after midnight, possibly because it reduces the chances of seeing the morning light, which resets the internal clock.”
Why the relationship between falling asleep and cardiovascular disease was greater in women is unclear.
Dr. Plans said, “There may be a gender difference in how the endocrine system responds to a disruption in the circadian rhythm.”
Alternatively, the older age of the study participants could be a confounding factor, “as the cardiovascular risk of postmenopausal women increases – which means that there can be no difference in the strength of the association between women and men”.
If the results hold up similarly structured studies in the future, “sleep timing and basic sleep hygiene could be a cost-effective public health goal to reduce the risk of heart disease”.