Sleep for 8 Hours

The idea that we should divide our days into “eight hours’ labour, eight hours’ recreation and eight hours’ rest” dates back to the 19th century. It might be neatly divisible, but it’s contestable.

Can you count on it?

Most sleep scientists consider seven hours the benchmark for better health. But it’s not just about how much you sleep, but when. A recent study used Fitbit data to measure the impact of sleep times on resting heart rates (RHR), a marker of overall fitness. Going to sleep 30 minutes later than usual was linked to a higher RHR all night, persisting into the day.

“Having consistent waking and sleeping times is crucial,” says Dr Conor Heneghan, director of research and algorithms at Fitbit, who has collected data on more than 10.5 billion nights of sleep. His research shows consistency correlating with quality, which means more time spent in the

“deep” and “REM” stages, associated with repair and memory consolidation. A study in the American Journal of Health Promotion found that people with more than 90 minutes of variation in sleep timings are also likely to have higher body fat than those with less than 60.

The expert update

Set a 30-minute window for your sleeping/waking times. We often wake on and off for about 55 minutes per night, so add a buffer for that.