Smart Watch Steps
What is the best time to go to bed at night? British researchers, who studied 88,000 volunteers, found that this point appeared to fall between 10 and 11 o 'clock, and that getting enough sleep during this time was linked to better heart health.
Synchronising sleep with the body clock could explain the link with reduced risk of heart attacks and strokes, according to the UK Biobank team.
The body's natural 24-hour rhythm is important for maintaining health and alertness during the day. It also affects markers such as blood pressure.
"Ideal" bedtimes and heart health
The researchers, whose analysis is published in the European Heart Journal, used wrist monitors similar to wristwatches to collect data on volunteers' sleep and wake times for a week.
The researchers then followed the heart and circulatory health of the volunteers for an average of six years and found a total of more than 3,000 people had developed cardiovascular disease.
Many of these cases were in people who went to bed later or earlier than the "ideal time" between 10 and 11 am.
The association held even after adjusting for sleep length and sleep patterns.
The researchers tried to control for other factors known to affect heart health, such as age, weight and cholesterol levels, but stressed that their study could not prove a cause-and-effect relationship between bedtime and heart disease.
While they don't draw conclusions about cause and effect, the results at least suggest that both early and late bedtimes are more likely to interfere with the body clock, which could adversely affect cardiovascular health, said lead researcher Dr. David Plants of the University of Exeter.
What is the biological clock?
Circadian rhythms have been known for a long time and is an accepted scientific fact. The body clock controls and influences the body's health 24 hours a day, from metabolism to sleep.
And humans aren't the only creatures with built-in circadian rhythms. Any life that relies on sunlight for energy is believed to have some sort of circadian rhythm to make the most of light and darkness.
The body clock, located in the brain's hypothalamus, acts as a conductor and sends regulatory signals throughout the body at different times of day. Sleep stress builds up from the moment you wake up in the morning, but you usually don't fall asleep until your body clock tells you it's time to rest.
Is it most dangerous to go to bed after 12 AM?
'The most dangerous time is after midnight because it has the potential to affect the body clock by reducing a person's likelihood of seeing morning light,' Dr Plants said.
In addition to waking people up in the morning, natural light can actually help people sleep at night. Because an hour of daylight exposure will kick-start the brain and reset the body clock to help increase sleepiness when you go to bed at night.
Kathleen Kiblin, senior cardiac nurse at the British Heart Foundation, said the large study showed that for most people going to bed between 10pm and 11pm was probably the best time for long-term heart health.
But Giblin said it's important to remember that this study can only show an association between bedtime and heart health, not a cause-and-effect relationship.
"Get enough Sleep"
More research is needed, including on bedtime and sleep duration, which are related to heart and circulatory disease.
Getting enough sleep is important for overall health, as well as heart and circulatory health, Giblin said. Most adults should aim for seven to nine hours of sleep a night.
"Sleep isn't the only factor that affects our heart health. Knowing your lifestyle, such as blood pressure and cholesterol readings, is equally important. Maintaining a healthy weight, exercising regularly, cutting down on salt and alcohol and eating a balanced diet can also help keep your heart healthy," says Giblin.