Bad news for coffee lovers, and in general for all those who take advantage of a cup of coffee to wake up in the morning. Or, even more generally, to keep awake.

A very precise study by the University of Bath , by its Center for Nutrition, Exercise & Metabolism, has in fact established that coffee slows down the metabolism if taken after a sleepless night or almost. We know that lack of sleep leads to an increase in stress hormones, cholesterol, blood sugar and the tendency to gain weight around the abdomen. But according to the authors of the study, it’s not just the lack of sleep that causes problems, but what you drink as soon as you get up.

Let’s see why.

Here’s how coffee slows down your metabolism

Scientists at the University have in fact found that the negative effects on metabolism caused on sleep deprivation, amply demonstrated in numerous studies, actually occur more easily in one circumstance.
That is, if after a night in which we slept little or nothing, we first drink a coffee when we get out of bed.

But drinking coffee first thing in the morning if we don’t get enough sleep leads to a major dysregulation of blood sugar. Which then gets worse throughout the day.

The researchers arrived at these results after dividing a sample of about 30 participants into 3 groups, depriving them of sleep in two out of three cases, and then recording the presence of metabolic alterations between before and after.

In the first group who had been getting enough sleep and in the second who had worked at night, skipping sleep, in the morning they were given a sugary drink before ingesting any other food.

The third group, who like the second had not slept at all, instead took bitter coffee, without milk or sugar, first thing in the morning.

Subsequently all three groups ate the same breakfast. But the group that drank the black coffee had the worst scores for insulin and blood sugar, despite not consuming sugars before breakfast.
In this group, blood sugar increased by 50%.

The researchers’ explanation is that coffee, in previous stressful conditions caused by lack of sleep, worsens postprandial blood sugar. On the one hand, alarm clock. On the other hand, coffee slows down the metabolism.

Researchers therefore recommend never having coffee in the morning as the first thing you wake up to. But always take it after breakfast. Or don’t take it at all.

See also: Does coffee make you lose weight? Pros and cons.