Study: When You Go to Sleep More Important Than How Long You Sleep

• Sleep is important for regulating metabolic health, and a combination of both general and more personalized sleep guidelines is likely to be necessary to enable individuals to minimize their risk of metabolic disease, such as diabetes, high blood pressure (hypertension) and obesity.
• ZOE PREDICT is the world’s largest study to gather in-depth, detailed data on sleep and nutrition. This particular study on sleep is the largest to use objective measures of sleep, continuous glucose monitoring and standardized metabolic challenge tests.
• Having a poor night’s sleep was associated with a less healthy blood sugar response to breakfast the following morning, no matter what the individual’s breakfast of choice.
• Having an irregular weekly sleep pattern was associated with poor blood sugar control, potentially leading to short and long-term health challenges.  
• This study’s findings may inform lifestyle strategies to improve postprandial blood glucose levels, focusing on earlier bedtime routines and maximizing high-quality uninterrupted sleep. 

A good night’s sleep has long been known as a core part of a healthy lifestyle. Although how sleep fits with diet and physical activity, has not been entirely clear. In fact, researchers have previously found that sleeping badly or too little is linked to poor blood sugar control in people with diabetes but the extent to which this relationship held up in healthy people has largely been unknown until now. ZOE’s team of researchers used data from the ZOE PREDICT study, where 953 healthy volunteers were followed over the course of two weeks. During this time, the participants ate a range of standardized meals, and wore blood glucose and movement monitors to measure their blood sugar responses and sleep (note: sleep was not manipulated for the experiment).

The scientists measured the total duration from the time participants went to bed to the time they woke up, as well as their quality of sleep. They then analyzed people’s sleep patterns over two weeks, and compared them against their blood sugar responses to meals containing specific amounts of carbohydrates, proteins and fats.

Connecting the Dots

Through their research, the scientists found that across all participants, going to bed earlier rather than sleeping longer is likely to be better for metabolic health –  a state that is measured by a series of factors that show how healthy you are now, as well as how likely you are to develop serious chronic conditions later in life. Participants who went to bed later tended to have worse blood sugar responses to breakfast the following day, even if they woke up late, compared with people who slept for the same amount of time but went to bed earlier in the evening. 

Additionally, the data revealed that having a disrupted night’s sleep was associated with a less healthy blood sugar response to breakfast the next day. Alternatively, on an individual basis, sticking to one’s normal sleep routines and avoiding unusually late nights led to a healthier blood sugar response to breakfast the following morning. This is important because unhealthy blood sugar responses after eating have been linked to an increased risk of developing type 2 diabetes or heart disease. 

Further, having an irregular weekly sleep pattern with inconsistent bedtimes and variable sleep duration was also associated with poorer blood sugar control. This could help to explain ‘social jetlag,’ which is brought on by the shift in sleep schedule that many people experience on their days off, compared to work days, and has been shown to be associated with poorer health, worse mood, and increased sleepiness and fatigue.

Lastly, the team found that high fat and high carbohydrate breakfasts led to better controlled blood sugar responses than just having a sugary drink. This finding could be particularly relevant for people who turn to energy drinks or candy for breakfast as a pick-me-up after a late night. If repeated regularly, poor blood glucose responses can raise the risk of metabolic health problems such as diabetes, obesity and heart disease. Thus, maintaining blood sugar levels is a crucial part of staying healthy and a key component of the ZOE program for this reason. 

These results underscore the essential role that sleep plays in a person’s wellbeing and ability to achieve a healthy lifestyle, as well as the importance of getting sufficient, high quality sleep and the value of turning out the lights earlier when possible.

Lead researcher on the study and member of ZOE Scientific Advisory Board, Professor Paul Franks from Lund University in Sweden, said: “For most people, both sleep duration and timing are modifiable factors, so being sleep-deprived, or having a disrupted sleep schedule is up to us to change.” Franks added, “Borrowing from your awake time and racking up sleep loans are never made without incurring interest. Even just one night affects the way our bodies metabolize food and how well blood sugar levels are controlled.”

Dr. Sarah Berry, reader in nutritional sciences in the Department of Nutritional Sciences at King’s College, London, and Lead Nutritional Scientist at ZOE, acknowledged, “Sleep is a key pillar of health alongside diet, physical activity and mental health. Yet, one in three people don’t get enough sleep. People who don’t get enough sleep have a 40 percent higher risk of being obese and are at much higher risk of cardiovascular disease and diabetes. These same people tend to eat more calories, choose unhealthy snacks, have less variety in their diet and have a poor diet quality with lower fiber and fruit and vegetable intake. In short, our study shows that sleep should get more attention.”

Tim Spector, scientific co-founder of ZOE and professor of genetic epidemiology at King’s College London, noted, “As with diet, there is no one-size-fits-all approach to recommend our precise hours of sleep. But, now we can confirm there is a recommended approach to when and how we sleep.” Spector continued, “For people to feel empowered and confident in their ability to take action with their health, education is critical. Our cutting-edge research combined with ZOE’s personalized insights help us meet people wherever they are on their journey and provide them with a science-backed roadmap to achieve change and thrive.” 

5 Science-Backed Sleep Tips to Support Metabolic Health

• Order Up Consistency: Create a sleep routine that works and stick to it throughout the week.
• Make an Early Reservation…with Your Bed: Go to bed earlier each night rather than hit snooze the next morning.
• Set the Mood: Make sure the bedroom is quiet, dark and cool, avoid eating and drinking late at night, and plan enough time to unwind and relax before hitting the hay.
• Start The Day Right: Results from ZOE’s PREDICT study show that what a person eats is as important as when a person eats. Since the effects of food vary widely between individuals, grab a breakfast that is healthy for your body (think: fruits and vegetables) rather than a high-carb breakfast for the best energy boost in the morning. 
• Know Your Body: Take a comprehensive test that identifies the prevalence of “good” and “bad” bacteria in your gut that are linked to metabolic health, as well as blood sugar and blood fat responses to food so you can take control of your own health. 

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