London, Jan 23 (IANS): Consuming energy drinks even once a month can lead to poor sleep quality and insomnia, finds a study.

Marketed as mental and physical pick-me-ups, energy drinks are popular with college students and young people in general.

The study, published in the open access journal BMJ Open, showed that the higher the frequency of consumption, the fewer hours of nightly shut-eye clocked up.

Even just the occasional can one to three times a month was linked to a heightened risk of disturbed sleep, the findings indicated.

It is because energy drinks contain an average caffeine content of 150 mg per litre as well as sugar, vitamins, minerals and amino acids in varying quantities, explained researchers from the universities of Oslo and Bergen in Norway.

While there was some evidence to suggest that they reduce sleep quality, it wasn't clear exactly which aspects of sleep might be more or less affected, or whether there are any sex-specific differences in these effects.

To explore, the researchers drew on 53,266 young people aged 18- to 35-year-old in Norway.

The participants were asked how often they consumed energy drinks, with the response options of daily, weekly (once; 2-3 times; 4-6 times), monthly (1-3 times), and seldom/never.

They were also asked detailed questions about their usual sleep patterns: when they went to bed and got up; how long it took them to fall asleep (sleep latency); wakefulness after going to sleep. Sleep efficiency was then calculated from total nightly hours of sleep vs. time spent in bed.

Insomnia was defined as experiencing difficulties falling and staying asleep and waking early on at least three nights of the week, plus daytime sleepiness and tiredness for at least three days of the week, for at least three months.

Of those who said they did drink these beverages, 5.5 per cent of women said they drank them 4-6 times a week and just over 3 per cent reported daily consumption. The comparable figures for men were 8 per cent and 5 per cent, respectively.

But there was a clear dose-response association for both sexes between energy drink consumption and fewer hours of sleep.

Both men and women who reported daily consumption slept around half an hour less than those reporting only occasional or no consumption.

Similar associations were also observed for waking after falling asleep and taking longer to fall asleep.

And increasing consumption was associated with a corresponding increase in both nocturnal wake time and time taken to fall asleep -- poorer sleep efficiency, the researchers said.