If you’re like many people, a night of poor sleep likely has you reaching for a strong cup of coffee to help wake you up. New research, however, suggests that this tactic may have some unintended consequences, particularly when it comes to your metabolism and blood sugar.

Researchers from the Centre for Nutrition, Exercise and Metabolism at the University of Bath in the United Kingdom looked at the effect of broken sleep and morning coffee across a range of different metabolic markers.

Writing in the British Journal of Nutrition, the researchers found that while one night of poor sleep has a limited impact on metabolism, drinking coffee as a way to feel more alert in the morning can have a negative effect on blood glucose (sugar) control.

Given the importance of keeping blood sugar levels within a safe range to reduce the risk of conditions such as diabetes and heart disease, researchers say these results could have “far-reaching” health implications, particularly given the global popularity of coffee.

The Study

For their study, researchers at the University of Bath asked 29 healthy men and women to undergo three different overnight experiments in a random order:

  • In one condition, participants had a normal night’s sleep and were asked to consume a sugary drink upon waking in the morning.
  • On another occasion, participants experienced a disrupted night’s sleep (where the researchers woke them every hour for five minutes); upon waking in the morning, they were given the same sugary drink.
  • On another, participants experienced the same sleep disruption (i.e., being woken throughout the night), but this time were first given a cup of strong black coffee 30 minutes before consuming the sugary drink.

In each of these tests, blood samples from participants were taken following the sugary drink, which contained about the same number of calories that might typically be consumed for breakfast.

When compared to a normal night’s sleep, the researchers found that one night of disrupted sleep did not worsen participants’ blood glucose/insulin responses at breakfast. Past research suggests that losing many hours of sleep over one and/or multiple nights can have negative metabolic effects, so it is reassuring to learn that a single night of fragmented sleep (e.g., due to insomnia, noise disturbance or a new baby) does not have the same effect.

However, strong black coffee consumed before breakfast substantially increased the blood-glucose response to breakfast by around 50%. Although population-level surveys indicate that coffee may be linked to good health, past research has previously demonstrated that caffeine has the potential to cause insulin resistance. This new study reveals that the common remedy of drinking coffee after a bad night’s sleep may solve the problem of feeling sleepy but could create another by limiting your body’s ability to tolerate the sugar in your breakfast.

“We know that nearly half of us will wake in the morning and, before doing anything else, drink coffee—intuitively, the more tired we feel, the stronger the coffee,” explains Professor James Betts, codirector of the Centre for Nutrition, Exercise and Metabolism at the University of Bath who oversaw the work. “This study is important and has far-reaching health implications, as up until now we have had limited knowledge about what this is doing to our bodies, in particular for our metabolic and blood sugar control.”

What Does the Research Mean for Health and Exercise Professionals?

“These results show that one night of disrupted sleep alone did not worsen participants’ blood glucose/insulin response to the sugary drink compared to a normal night of sleep, which will be reassuring to many of us,” says lead researcher Harry Smith from the Department for Health at Bath. This is definitely news worth sharing with your clients, particularly at a time when stress levels are particularly high and a bad night’s sleep has become a common occurrence for many people.

Knowing how to respond appropriately to a night of poor sleep and get your energy back on track for the day ahead can be incredibly helpful. As Betts explains, blood sugar control is impaired when the first thing our bodies come into contact with is coffee, especially after a night of disrupted sleep. The solution? Educate your clients on the importance of eating first and then drinking coffee later if they feel they still need it. Knowing this, says Betts, can confer important health benefits.

Smith goes on to say that “there is a lot more we need to learn about the effects of sleep on metabolism, such as how much sleep disruption is necessary to impair metabolism and what some of the longer-term implications of this are, as well as how exercise, for instance, could help to counter some of this.”