A strong black coffee to wake up after a bad night of sleep could impair control of blood sugar levels, according to a study.
Researchers from the Centre for Nutrition, Exercise and Metabolism at the University of Bath examined the effect of broken sleep and morning coffee across a range of metabolic markets.
Their work, published in the British Journal of Nutrition, shows that one night of poor sleep had a limited impact on metabolism, but drinking coffee could have a negative effect on blood glucose control.
In the study, 29 healthy men and women underwent three different overnight experiments in a random order.
For one, participants had a normal night of sleep and were asked to consume a sugary drink on waking.
On another occasion, they experienced a disrupted night of sleep – being woken up for five minutes each hour – and were given a sugar drink in the morning.
The third test involved participants experiencing the same sleep disruption but being given a strong black coffee 30 minutes before consuming the sugary drink.
Blood samples from participants were taken following the glucose drink, which mirrored the calories of a typical breakfast, in each experiment.
Results showed that one night of disrupted sleep did not worsen the participants’ blood glucose responses at breakfast when compared to a normal night of sleep.
However, strong black coffee consumed before breakfast increased the blood glucose response to the drink by around 50%.
Professor James Betts, co-director of the Centre for Nutrition, Exercise and Metabolism at the University of Bath, said: “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.
“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.
“Put simply, our blood sugar control is impaired when the first thing our bodies come into contact with is coffee especially after a night of disrupted sleep.
“We might improve this by eating first and then drinking coffee later if we feel we still need it. Knowing this can have important health benefits for us all.”