Studies have increasingly documented the health implications of insufficient sleep, which include increased risk of diabetes, depression, cardiovascular disease and obesity.

But despite such findings, more than a third of us still fail to get the recommended 7-8 hours of sleep each night.

Whether lack of sleep is due to stress, late nights out or a sleep disorder, many people who fail to get sufficient shut-eye may find they have an increased appetite the following day, with a particular craving for unhealthy foods.

Now, Erin Hanlon, PhD, a research associate in endocrinology, diabetes and metabolism at the University of Chicago, IL, and colleagues may have shed light on why this is.

"We found that sleep restriction boosts a signal that may increase the hedonic aspect of food intake, the pleasure and satisfaction gained from eating," says Hanlon. "Sleep restriction seems to augment the endocannabinoid system, the same system targeted by the active ingredient of marijuana, to enhance the desire for food intake."

The researchers publish their findings in the journal Sleep.
Sleep deprivation increased circulating endocannabinoid levels by 33%

The team enrolled 14 healthy volunteers in their 20s, who were required to sleep in the University's Clinical Research Center over two separate 4-day periods.

Fast facts about sleep

    Americans sleep an average of 7 hours and 36 minutes a night
    On weekends or non-workdays, Americans sleep for around 40 minutes longer
    Women are more likely to report symptoms of insomnia than men.

Learn more about sleep

During one of the 4-day stays, subjects spent 8.5 hours in bed, sleeping an average of 7.5 hours a night. During the other 4-day stay, participants spent just 4.5 hours in bed, sleeping for an average of 4.2 hours each night.

For the duration of each stay, the researchers kept track of the participants' hunger and eating habits. During both stays, subjects ate identical meals three times daily, at 9 am, 2 pm and 7 pm, and after the fourth night's sleep, they were also offered various snack foods.

The researchers also measured levels of the hormones ghrelin and leptin; high ghrelin levels and low leptin levels have been associated with reduced sleep time and increased appetite in past studies.

Additionally, the team measured blood levels of the endocannabinoid 2-arachidonoylglycerol (2-AG), levels of which are normally low during the night and which gradually rise during the day, reaching their peak by early afternoon.

The researchers identified normal patterns of 2-AG levels after participants had a good night's sleep. With reduced sleep, however, the researchers identified a 33% rise in 2-AG levels; such levels peaked at around 2 pm - around 90 minutes later than with normal sleep - and remained high until around 9 pm.

What is more, the team found that after reduced sleep, subjects reported a rise in hunger levels, particularly after consuming their second daily meal, which the researchers note coincided with the time when 2-AG levels reached their peak.

This suggests that sleep deprivation increases appetite in a similar way to how tetrahydrocannabinol (THC) - the primary active ingredient in marijuana - increases appetite: by targeting the endocannabinoid system.
Reduced sleep may lead to weight gain by boosting desire for fatty foods

When offered snack foods after the fourth night's sleep, the team found that participants were more likely to consume them after being sleep deprived - despite eating a meal 2 hours previously. They were also more likely to opt for snacks that contained around 50% more calories and twice the amount of fat after lack of sleep.

The researchers say their findings indicate that lack of sleep increases circulating endocannabinoid levels, which "could be a mechanism by which recurrent sleep restriction results in excessive food intake, particularly in the form of snacks, despite minimal increases in energy need."

"One study has reported that each added hour of wakefulness uses about 17 extra calories. That adds up to about 70 calories for the 4 hours of lost sleep," notes Hanlon.

"But, given the opportunity, the subjects in this study more than made up for it by bingeing on snacks, taking in more than 300 extra calories. Over time, that can cause significant weight gain."

In a commentary linked to the study, Frank Scheer, PhD, of the Medical Chronobiology Program at Harvard University's Brigham and Women's Hospital in Boston, MA, says the findings "support the novel insight that sleep restriction leads not only to increased caloric intake, but also to changes in the hedonic aspects of food consumption."

Hanlon adds:

    "[...] if you have a Snickers bar, and you've had enough sleep, you can control your natural response. But if you're sleep deprived, your hedonic drive for certain foods gets stronger, and your ability to resist them may be impaired. So you are more likely to eat it. Do that again and again, and you pack on the pounds."

The researchers admit that there are some limitations to their study, such as the small sample size and short duration.

Still, they believe that the results are significant and are "relevant to normal life conditions."

Earlier this year, Medical News Today reported on a study that found just 1 day of unhealthy eating can affect sleep quality.