Why eight hours really is the perfect sleep length

There’s a reason eight hours is the holy grail of sleep time [Photo: Getty]

Sleeping for over 10 hours a night – or fewer than six – may increase the risk of heart disease, new research has revealed.

We’ve always believed that eight hours worth of shuteye is basically the sleep dream.

Long enough to get our beauty sleep, but not so long that we get that groggy, can’t-wake-up feeling.

But turns out there’s a much more important reason why eight hours is the holy grail of snooze length.

A study by researchers from Seoul National University, and published in the journal BMC Public Health, found that women who sleep for ten hours were 40 per cent more likely to have at least three health conditions linked to premature mortality.

These include a large waist, high blood pressure, elevated levels of fat or sugar in the blood.

Men didn’t escape the too much/too little sleep trap either as the research also revealed men who habitually slept fewer than six hours every 24 hours were also associated with an elevated waist circumference.

While those catching 10 hours of ZZZs were associated with elevated triglycerides, which is often a sign of other conditions that increase the risk of heart disease and stroke including something known as metabolic syndrome.

Metabolic syndrome (MetS) is defined as a metabolic disorder consisting of at least three of the following: elevated waist circumference, high triglyceride levels, low high-density cholesterol levels, hypertension and high fasting glucose.

It isn’t a condition itself, rather a collection of factors that dramatically increase your risk of developing type 2 diabetes, stroke, and heart disease.

For the study, researchers analysed 133,608 people aged between 40 and 69 years old.

The participants’ were asked how long they spent sleeping each day in the past year, including daytime naps.

Blood, DNA and urine samples were also collected.

Eight hours of sleep is spot on

From the data gathered researchers determined that fewer than six hours of sleep a night and more than 10 is linked to metabolic syndrome and the conditions that fuel it, and that the effects vary by gender.

“We observed a potential gender difference between sleep duration and metabolic syndrome, with an association between metabolic syndrome and long sleep in women and metabolic syndrome and short sleep in men,” Claire E. Kim, lead author of the study, said in a statement.

On average, adults are recommended to try to catch between seven to nine hours of sleep every night.

“This is the largest study examining a dose-response association between sleep duration and metabolic syndrome and its components separately for men and women,” Kim said.

Researchers concluded that after allowing for sociodemographic and lifestyle factors, a link between sleep duration and metabolic syndrome could be observed.

Though it isn’t yet clear why sleep duration might be linked to metabolic syndrome, researchers did offer a couple of suggestions including the fact that too little sleep may unbalance the hunger hormones ghrelin and leptin, making you to eat more. It could also increase the stress hormone cortisol, which puts an increased strain on the body.

But further studies using multiple measurements of sleep duration (i.e. sleep diaries and actigraphs) would be needed to further assess the casual relationship between sleep duration and MetS and its components.

Until then, we’re not taking any chances.

See you in eight hours!

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