A lack of sleep makes people crave junk food and spend more money to get their hands on it, a study has found.

Tiredness can boost activity in areas of the brain related to appetite and comfort eating and hormones that tell us when we are hungry, Daily Times says.

The disruption to the body’s normal functions can lead to an increased likelihood of overeating, and over time, obesity, the researchers suggested.

It may explain why some people are more likely than others to reach for the biscuits by the afternoon.

Britain and the United States are among the most overweight and sleep deprived nations in the world – and evidence is growing the two are linked.

Dr Julia Rihm, lead author of the study and her team enrolled 32 healthy men aged between 19 and 32 for the study.

Participants visited their laboratory for a normal dinner of pasta and veal in a creamy mushroom sauce with an apple and strawberry yoghurt, on two separate nights.

On each visit they were instructed to either return home after the meal to sleep normally or to spend the night at the lab, where they would be kept awake.

Their desire for snack foods, brain activity, and hormone levels were assessed the next morning.

Then they were given three euros to spend on snacks – such as popular brands of German chocolate bars or chips – or everyday household items or university merchandise.

In an online auction, images of the goods flashed up on screen with prices going up in stages of 0.25 euros.

The participants were told to bid the maximum amount they were willing to spend on the item and that they could spend their total of three euros if they wanted to.

Only after sleep deprivation were the participants willing pay extra for the junk food items – which they were allowed to eat afterwards.

Using Magnetic Resonance Imaging brain scans, the team showed losing sleep fired neurons in their amygdala and hypothalamus.