Charging a phone or tablet in the bedroom may cause weight gain, new research suggests.
The light from gadget screens and computers – or street lights – can cause weight gain because it harms the production of 'sleep hormone' melatonin, experts say.
Healthy levels of melatonin promote regular sleep patterns, which helps the body convert food and drink into energy efficiently.
If the production of melatonin is harmed, the body's sleep cycles are disturbed and this stops the body processing food as efficiently.
Scientists at the University of Granada, Spain, discovered that injections of melatonin helped combat obesity and diabetes in rats by regulating their systems.
The new study, carried out by experts at Manchester University, is looking at how regulating sleep patterns might help patients who already have diabetes - a disease often linked with obesity.
Their work is still ongoing, but so far the team has found a link between circadian patterns - the regulation of our internal clocks and our sleeping - and diseases like obesity and diabetes.
Previous U.S. research has already suggested that using a computer or smartphone at night can cause weight gain as it increases hunger levels - even after eating a meal.
Dr Simon Kyle, a sleep researcher at the university's School of Psychological Sciences, said blue light - the kind emitted by phones and laptops - is the most damaging to our sleep, and consequently our metabolism.
Therefore improving sleep could help stem the obesity epidemic, he said.
Professor Kyle said: 'We are interested in how an alteration in the sleep-wake pattern may be involved in the onset of diabetes and obesity and if, when you improve the timing of sleep you can also have a positive effect on conditions like diabetes and obesity.
HOW USING GADGETS AT NIGHT INCREASES HUNGER
Using a computer or smartphone at night can cause us to pile on the pounds, research found.
The study found a link between blue light exposure - blue light is emitted by smartphones and tablets - and increased hunger
It found that exposure to the light increases hunger levels for several hours and even increases hunger levels after eating a meal.
Results of the US study show that blue-enriched light exposure, compared with dim light exposure, was associated with an increase in hunger that began 15 minutes after light onset and was still present almost two hours after the meal.
Study co-author Ivy Cheung, of Northwestern University, in Chicago, said: ‘A single three-hour exposure to blue-enriched light in the evening acutely impacted hunger and glucose metabolism.
'A lot of people are interested in this at the moment given that as a 24-hour society sleep deprivation is increasing and we are exposing ourselves to artificial light at night.'
'We are trying to extend the waking day into our sleep period and there is not enough protection of sleep'
'There is a lot of research showing we are meant to be asleep at night when darkness falls and melatonin rises, and when the sun rises the melatonin is blocked by the sun. This light-dark cycle is good for our bodies to predict changes in the environment.
'So if you start sleeping shorter, or receive light at the wrong time late into night, it disrupts melatonin secretion and that could contribute to alterations in metabolism.'
Blue light can also keep a person's mind buzzing, further preventing them from sleeping, he added.
Professor Kyle said he advised avoiding using phones, tablets and laptops in the evenings before bed.
He said: 'In the couple of hours before bedtime, I try and enforce reduced light conditions - and that means an absence of computers, phones and ipads that emit the blue wavelength light.
'There should be a huge public health shift in how we are viewing the sleep period and the hours before it.
'There is strong basic science and data to show the association between sleep interference and disease.'
He added: 'If you can have complete darkness at night time you might be able to recreate time's pre-industrial period and have a stab at improving the obesity epidemic.'
