Do you go to bed at the same time every night? If you are like most people in the industrialized world, the answer to this question is likely "no." Electrical lights and smart devices give us the means to stay awake well past dark and plenty of ways to entertain ourselves while doing so. The result is that most adults and even many children lack a consistent bedtime, which is a dilemma that a recent study suggests may have a negative effect on cardiovascular health. Could going to sleep at the same time each night—a habit common in our ancestors who lived by the light of the sun—be a crucial factor in preventing heart disease?
The Benefits of Keeping a Consistent Bedtime
Most children have a set bedtime, but as adults, we generally give up this habit. We go to bed when we feel ready for sleep, which varies from night to night. A new study published in the journal Hypertension suggests that bedtime may be more important than we could have ever predicted. In the study, healthy volunteers underwent a series of blood tests, then were given a new sleep regimen with a constantly changing bedtime. After just eight days of a forced change in bedtime, these people had increased norepinephrine, a catecholamine which increases heart rate and has been found to contribute to heart disease in a variety of ways. These people also showed decreased vagal activity, which is significant because the vagus nerve is an important cardiovascular depressant.
Vagal activity is particularly important because this type of nervous activity generally occurs during deep sleep. The results of this study suggest that people who change their bedtime on a regular basis do not get as much deep sleep, which is when the heart regenerates itself after a long day. During deep sleep, vagal activity slows heart rate and blood pressure, reducing demands on myocardial muscle. This gives our heart muscle a chance to clean out metabolites and other biochemicals that accumulate throughout the day as well as providing a needed rest to muscles that maintain our lives 24 hours a day.
Sleeping the Stress Away... Or Not
This study adds to a growing body of evidence that a lack of regular sleep is bad for the heart and blood vessels. The heart is primarily governed by the two branches of the autonomic nervous system. The parasympathetic branch of this system releases hormones that encourage rest and regeneration, as well as digestion of food and other important activities. On the other hand, the sympathetic nervous system revolves around fight or flight. The hormones released by this system generally function as stress hormones. While stress hormones are important in escaping a real physical threat such as a threatening mastodon, they are often maladaptive in the modern world.
When we do not get enough sleep, the sympathetic nervous system dominates our autonomic system. The result is that we have increased levels of stress hormones, which create long-term damage to our cardiovascular systems. Getting a good night's sleep—including going to bed at a regular time—may be one of the best things we can do to maintain a healthy heart.
The Magic of Sleep
Sleep is a time for mental regeneration, but it appears to be just as important for physical regeneration. Our cardiovascular system is not the only organ system that needs some time at night to regenerate cells and clean out toxic metabolites from the activity of the day. Neural cells also appear to repair damage and replace worn-out cells while we sleep. Even hepatocytes, the cells of the liver, rely on sleep cues from master clocks in the human brain to determine when to rebuild and undergo repair processes. Our bodies must maintain a healthy circadian rhythm in order to undergo crucial processes that keep our cells healthy amidst the challenges of modern life.
Sleep disorders do not just make us more fatigued the next morning, but can potentially affect almost every cell in our body. Setting a regular bedtime may be a healthy lifestyle change that is as important as eating a healthy diet and getting regular exercise.