According to a study published in European Heart Journal -- Digital Health today, a lower chance of developing heart disease is associated with sleeping between 10:00 and 11:00 p.m., which was published by the European Society of Cardiology (ESC).
Dr. David Plans, University of Exeter, UK, said that the body has a 24-hour internal rhythm called the circadian rhythm which regulates physical and mental functioning. Our study does not prove causation, but the results indicate that bedtimes of either early or late may disrupt the body's clock, which could have adverse effects on cardiovascular health.
Numerous studies have examined the relationship between sleep duration and cardiovascular diseases, but the relationship between sleep timings and heart disease has not been explored. This study looked at the relationship between objectively measured and self-reported sleep onset in large samples of adults.
This study involved 88,026 people from the UK Biobank who were recruited between 2006-2010. The average age of the participants was 61 (range 43-79 years), and 58% of them were women. A wrist-worn accelerometer was used to collect data on sleep onset time and waking time over seven days. Participants were asked to complete questionnaires and demographic information. The participants were then followed-up for a new diagnosis in cardiovascular disease. This was defined as heart attack, heart failure chronic ischaemic, stroke and transient Ichaemic attack.
3.6% of the 3,172 participants who developed cardiovascular disease during a follow-up period of 5.7 years had a mean age of 5.7 years. The incidence was highest among those who slept at night or later, and the lowest among those who slept between 10:00 and 10:59 am.
After adjusting for age and sex, sleep duration, cardiovascular events, and self-reported chronotype (early birds or night owl), body mass index, smoking status, socioeconomic status, and blood pressure, the researchers looked at the relationship between sleep onset, cardiovascular events, and sleep onset.
A sleep onset between 10:00 and 10:59pm was associated with a 25% greater risk of developing cardiovascular disease. There was also a 12% higher risk for 11:59 to 11:00 pm, and a 24% increased risk of falling asleep before 10:00pm. A further analysis using sex revealed that the association between increased cardiovascular risk and sleep onset earlier than 10:00 pm was more significant in women than it was for men.
Dr. Plans stated that "our study suggests that the optimal time to fall asleep is at a particular point in the body’s 24-hour cycle. Any deviations could be harmful to your health." Because it reduces the chance of seeing the morning light, the body clock resets, the riskiest time to go to sleep was after midnight.
Dr. Plans said that it is not clear why women have a stronger association with sleep onset and heart disease. Dr. Plans stated that it could be due to differences in the way the endocrine systems responds to disruptions in circadian rhythms. Alternately, older age could be a factor. Women's cardiovascular risk rises after menopause. This may mean that there is no difference in strength of the association between men and women.
He concluded that, "even though the findings don't show causality," sleep timing was identified as a possible cardiac risk factor -- independent from other risk factors or sleep characteristics. If these findings are confirmed by other studies, basic sleep hygiene and sleep timing could be a low cost public health target to lower the risk of developing heart disease.