Insufficient sleep has been known as detrimental to a person’s health, resulting in increased irritability, obesity, high blood pressure, diabetes, and heart disease. Never before have we heard of too much sleep having negative effects.
However, over 10 years of research show that adults who sleep less than six hours or more than eight have an increased risk of early death compared to those who sleep between six and eight hours.
In other words, those who are outside the six-to-eight hours of sleep each night have an increased mortality risk.
The study shows that 12% of short sleepers died early compared to medium sleepers, while 30% of long sleepers died early compared to medium sleepers.
Such numbers make short sleep or longer sleep a risk factor similar to drinking several units of alcohol per day.
Prof Franco Cappuccio, professor at the University of Warwick, has analyzed 16 studies, in which overall more than a million people were asked about their sleeping habits and then followed up over time.
Cappuccio put the people involved into three broad groups: those who said they slept less than six hours a night, those who said they slept for between six and eight hours, and those who said they slept for more than eight hours.
He has been aware of the propensity longer sleepers have to become depressed, or resort to sleeping pills. His theory says that those sleeping more than eight hours on a regular basis may already have an underlying health problem that does not show any symptoms yet. In short, it is not the length of the sleep, but the hidden, unknown illness.
Apparently people have a general tendency to overestimate how long we’ve been asleep. We are also not good at estimating the quality of sleep, and all experts seem to agree it could affect your health, but it’s even harder to measure than how long you sleep.
Another caveat is that babies, children and teenagers all have different sleep requirements than adults.
If less than six hours is too little sleep for an adult while more than eight hours is too much, scientists are looking for the healthy amount of sleep.
The magic number, according to Dr Gregg Jacobs, of the Sleep Disorders Center at the University of Massachusetts Medical School may actually be seven.
“Seven hours sleep keeps turning up over and over again,” he says, pointing to the National Sleep Foundation’s annual poll of a random sample of adults in the US.
“The typical adult today [in that poll] reports seven hours of sleep. And that actually seems to be the median sleep duration in the adult population around the world. That suggests there’s something around seven hours of sleep that’s kind of natural for the brain.”