Researchers to teens: get to bed – it’s good for your blood sugar

“Go to bed!” — it’s a phrase most teenagers have heard countless times. For many young people, bedtime is easily pushed aside in favour of Netflix, gaming or just another scroll on their phone. Most already know that sleep is important for concentration, mood and learning. Now, there’s new evidence that it matters for metabolic health too.

A new study from the University of Copenhagen and the COPSAC research unit at Herlev and Gentofte Hospital shows that longer sleep is associated with fewer fluctuations in blood sugar – even among healthy 18-year-olds.

Large swings in blood sugar can increase inflammation and place strain on the metabolism, potentially contributing over time to conditions such as obesity and diabetes.

The link between sleep and metabolic diseases is not new. However, most previous studies have focused on middle-aged adults or individuals at increased risk of diabetes.

“For most 18-year-olds, diabetes feels like something far off in the future. We’ve known very little about what blood sugar variability means for this age group,” says senior author Professor Morten Arendt Rasmussen of the Department of Food Science at the University of Copenhagen and COPSAC. “But here we’re seeing similar patterns even in completely healthy young adults.”

More sleep – less sugar craving

The researchers tracked 206 Danish 18-year-olds over two weeks as they went about their normal routines. Participants wore activity trackers to monitor movement and sleep, along with glucose sensors that continuously measured blood sugar levels.

The results were clear: on days following longer sleep, participants had more stable blood sugar and fewer extreme spikes.

While the researchers had expected to find this link, they were surprised to discover that the relationship also worked in the opposite direction:

“The more stable participants’ blood sugar was during the day, the longer they slept the following night,” says first author and postdoctoral researcher David Horner from COPSAC at Herlev and Gentofte Hospital and the University of Copenhagen. “So this appears to be a two-way relationship — and that’s new.”

The study also found that more sleep was linked to slightly higher blood sugar levels during the morning and early part of the day — the opposite of what researchers had anticipated.

“However, that may actually be beneficial. Slightly higher blood sugar early in the day may help curb sugar cravings and thereby contribute to more stable blood sugar overall,” says Morten Arendt Rasmussen.

One possible explanation lies in how the body prepares to wake up. The researchers observed that blood sugar levels typically rose in the hours before waking — with a steeper increase after longer sleep.

“This may reflect the body getting ready for the day,” says Horner. “For example, the natural morning rise in the stress hormone cortisol can affect blood sugar around waking. Our findings suggest that the transition from sleep to wakefulness may be an important window for metabolism.”

Sleep: Netflix’s biggest competitor

The researchers emphasise that the study cannot determine the exact mechanisms behind the links between sleep and blood sugar. Behaviour may also play a part — including what and when young people eat, and how active they are.

Even so, the overall message is clear, says Rasmussen:

“We already know that sleep is important for mental wellbeing. Our study adds to our understanding of why sleep is also crucial for physical health – and that this applies even early in adulthood. It also highlights that many of the health problems we tend to see later in life may actually be established much earlier than we previously thought.”

In the long term, findings like these could help shape strategies to prevent obesity, type 2 diabetes and other metabolic diseases.

“If future studies confirm our findings, sleep could become an even more important factor in preventing disease and promoting health among young people. And taking action doesn’t require a new diet or an expensive gym membership – it really just comes down to going to bed,” says Morten Arendt Rasmussen.

Rasmussen adds with a smile:

“When Netflix’s CEO says that sleep is their biggest competitor, I’d very much like to be Netflix’s biggest competitor.”

THE STUDY AT A GLANCE

• 206 Danish 18-year-olds took part in the study.
• Sleep was measured using wrist-worn activity trackers.
• Blood sugar was monitored continuously using glucose sensors.
• Researchers analysed a total of 2,245 days of overlapping measurements.
• The study is published in the journal Sleep.
• In addition to COPSAC and the University of Copenhagen, researchers from the University of Washington School of Medicine (USA), Queen’s University (Canada), Harvard Medical School (USA), Steno Diabetes Center Copenhagen, and Herlev and Gentofte Hospital contributed to the study.
• The study was supported by, among others, the European Research Council (ERC), the Novo Nordisk Foundation, and the University of Copenhagen’s talent programme BRIDGE – Translational Excellence Programme, of which David Horner is a fellow.