Why you should go to sleep at the same time every night, according to experts

We all know getting enough sleep is essential for keeping our bodies and minds moving. Along with exercise, nutrition, and reducing stress, it's one of the four pillars of health. But provided you get those eight valuable hours, does it matter what time of night you fall asleep through the week? A new study suggests it does. 

Keeping bedtimes and wake times consistent - along with eating a balanced diet - can help reduce the risk of various diseases, including heart attacks, strokes, and obesity, given the link between sleep and our gut health. 

The study from Kings College London looked at nearly 1,000 adults involved in the ZOE Predict program, and found that small differences in our sleeping habits between Monday to Friday and the weekend could lead to unhealthy changes in our gut bacteria. Shockingly, they found that even 90 minutes of irregularity in the midpoint of our night's sleep over a normal week could make a big difference in the type of bacteria found in the gut.

But why? Essentially, going to sleep and waking up at different times leads to poorer quality sleep, and makes it more likely for us to reach for unhealthy food and drinks, which affects specific bacteria in our gut. Having a wide range of different bacteria in your gut is important, but getting the right mix is essential for preventing a number of diseases - including diabetes, heart disease, and obesity - previous studies by the likes of Houston Methodist Hospital and the University of Michigan Medical School have found.

The study found that the changes in our gut bacteria are down to a mixture of 'social jetlag' - the shift in the body's internal clock when sleeping patterns change through the week - and the associated changes in diet quality, eating habits, inflammation, and the make-up of our gut bacteria. For example, the less sleep (and good quality, undisrupted sleep) we have, the more likely we are to reach for foods and drink higher in sugar, salt, and saturated fats, and the less likely we are to eat fruit and nuts, which are high in fibre and contribute to healthy gut bacteria. 

"Fibre plays a crucial role in feeding the beneficial bacteria in the gut. Additionally, impaired or disturbed sleep can disrupt the appetite hormones causing a rise in the hunger hormone ghrelin and a reduction in the satiety hormone leptin," explains nutritionist Jenna Hope. "This means that you require more food to feel the same level of fullness as you would following a regular night's sleep."

Plenty of research has been done in the past looking at the damaging impact of persistent shift work on sleeping patterns and gut health but this study is one of a kind. Researchers looked at blood, stool, gut microbiome samples, and glucose measurements in those whose experienced irregular sleep compared to those with a regular sleep routine. It also focused on healthy individuals who banked more than seven hours of sleep a night through the week and specifically looked at how even small inconsistencies over several days can negatively affect the body. 

So what can we do to get back on track?

The researchers do confirm that we need more evidence on the subject before making firmer conclusions since the relationship between our sleep, diet, and gut bacteria is complicated. However, one thing is for sure: we need to learn how to sleep better by setting a regular sleep schedule, going to bed and waking up at the same time every day of the week (regardless of whether it's a weekday or weekend). Having good sleep hygiene, so we want to make this a priority in our lives, is also essential.

"If we sleep at regular times daily, it will support our gut health and increase microbiome diversity," says Farzanah Nasser, a nutrition and functional medicine specialist. "If we have irregular sleeping patterns, it can lower microbiome diversity."

Dr Sarah Berry from King’s College London and chief scientist at ZOE agrees. She says, “Maintaining regular sleep patterns, so when we go to bed and when we wake each day, is an easily adjustable lifestyle behaviour we can all do, that may impact your health via your gut microbiome for the better."