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Sleep is essential for healthy well-being, and we spend about one-third of our lives doing it. According to the Centers for Disease Control and Prevention, however, more than a third of American adults do not get enough sleep on a regular basis — at least 7 hours each night — to promote optimal health and well-being.
For many years at the height of my busy profession as a cardiologist, I would awaken at 5 a.m., exercise, get to work by 7, spend a full day at the hospital, return home for dinner, and then work until 11, totaling only five or six hours of sleep each night.
I suspect many readers keep a similar frenetic schedule due to work or social demands.
Recent information highlights how wrong that sleep pattern can be.
Researchers estimated the durations of total daily sleep and daytime naps based on the amount of time in bed and self-reported napping time and examined the associations between them and the composite outcome of deaths and major cardiovascular events (MACE) in 116,632 participants from seven regions. After a follow-up of almost eight years, they found that both shorter (six hours a day or less) and longer (more than eight hours a day) total sleep durations were associated with an increased risk of death and MACE. Daytime nap duration was associated with an increased risk in those with more than six hours of nocturnal sleep duration, but not in those sleeping six hours a day or less.
They concluded that total sleep duration of 6–8 hours per day is associated with the lowest risk of deaths and major cardiovascular events and that greater or lesser sleep durations were associated with increased risk.
Another study found similar results in almost 13,000 U.S. adults aged 30-74 years. Those who slept an average of seven hours a night had the lowest risk of subsequent cardiovascular disease, with increased risk for those who slept 6 or 8 hours a night.
An observational study from the University of Gothenburg in Sweden found that men in their 50s who slept five or fewer hours a night had double the risk for a major cardiovascular event by age 71 and were more likely to have high blood pressure or diabetes.
Too much or too little sleep may impact cardiovascular health by affecting inflammation, metabolism, weight gain, diabetes, blood pressure, damage to the heart or blood vessels, or modifying the nerves that regulate cardiovascular function.
As with all observational studies, causality cannot be proven for a variety of reasons. For example, total time in bed may not represent actual sleep time. Also, those who sleep longer may have underlying conditions that in themselves increase the risk of cardiovascular disease and mortality, so that prolonged sleep could be a marker of illness. Naps may be an indicator of poorer health.
Despite these study limitations, it is clear that too little or too much sleep may be risk factors impacting cardiovascular health. It makes sense to try for six to eight hours of sleep each night.