Quick answer: Most adults do best on around 7–8 hours of sleep a night. Both too little (under 7 hours) and too much (over 9 hours) have been linked to higher cardiovascular risk in research studies — and quality matters as much as quantity: being sedated (for example, by alcohol) is not the same as properly sleeping.
Why sleep matters more than you might think
Sleep is increasingly recognised as far more important than scientists previously thought. I have heard sleep called ‘the tide that raises all health ships’ and that is with good reason. It positively influences your mood, ability to perform complex tasks, allows your muscles to grow, repairs tissues. It even helps fight infection – in one study I read about, researchers demonstrated that good sleep can significantly reduce the recovery time from viral infections – which may be one reason why we often feel tired if we have an infection – it’s the body’s way of getting us to sleep.
How much sleep should you actually aim for?
But how long should we sleep for?
There’s actually a lot of science around sleep, and various researchers have tried to link the risk of heart disease and strokes to sleep quantity, with some suggesting that less than 6 or more than 8 increases those risks.
My own view on it is that it is much more complex than this. For example, sleep quantity and quality are different beasts. Being unconscious or sedated is different in its biological property to sleep. This is one reason why if you’ve had too much alcohol, you may well fall ‘asleep’ easily, but wake feeling un-refreshed. You are more likely sedated than properly asleep, and missing out on the benefits.
What do health guidelines recommend?
US health authorities recommend that adults ages 18 to 60 years should get at least 7 hours of sleep each night, but only 65.2% of adults surveyed in United States in 2014 reported that they consistently meet this standard. Inadequate sleep has been associated with a range of adverse health effects including diabetes, high blood pressure, mental distress, and an increased risk for accidents.
What does the research say about sleep and heart disease?
There is also mounting evidence supporting the notion that sleep duration may have an effect on cardiovascular health, with several studies linking both insufficient AND excessive sleep duration to an increased risk for cardiovascular disease.
A review of 74 studies indicated that self-reported sleep duration exceeding 8 hours per night—but not sleep duration <7 hours—was associated with an increased risk for all-cause mortality and cardiovascular events.An association was also observed between subjective poor sleep quality and an increased risk for coronary heart disease.
A couple of other studies have found that after adjusting for age, sex, physical activity levels, depression, and other potentially confounding variables, short sleep duration (ie, <7 hours per night) was found to be associated with a greater prevalence of previous heart failure, stroke, diabetes mellitus, heart attack and high cholesterol. In addition, longer sleep duration (ie, >9 hours per night) was found to be associated with a greater prevalence of previous stroke, coronary artery disease and heart failure.
More research is needed, but one wonders if the increased cardiovascular risks associated with short and long sleep durations may be attributed to factors such as metabolic impairment and lifestyle behaviours including poor dietary and exercise patterns. Sleep apnoea (stopping breathing at night) may be associated with longer sleep duration and has been linked to greater cardiovascular risk across various studies.
The bottom line
As you can see, there are some variations in the literature, but for most people a take home message of aiming for 8 hours sleep per night would seem reasonable. That’s certainly what I aim for, and always feel better for it.