A study by the universities of Tubingen and Lubeck in Germany and Uppsala University in Sweden shows people who are sleep-deprived are more likely to be hungry than those who have had enough shut-eye.

Sleep medicine research scientist Carmel Harrington, who has been studying the link between sleep and weight gain, delivered a lecture on the subject at the University of Canberra on Thursday.

Clinical trials show most people eat about 300 to 500 extra calories a day without an adequate night's sleep, Dr Harrington said. ''When we're sleep-deprived, our reward centres in the brain are very active, so we lose our ability to evaluate or make good food choices,'' she said.

Dr Harrington said the link between sleep and weight gain was first observed in a 1970s study of nurses on the contraceptive pill. In that study of more than 70,000 nurses, she said it was noted that the fewer hours they slept, the higher their body mass index rose, and this trend continued over the 15-year period of the study.

Director of the Sleep and Lifestyle Clinics at Phillip and at the University of Canberra, Grant Willson, said people with sleep problems were putting themselves at significant risk by not getting a check-up. ''Twelve per cent of men over 40 experience 30 airway blockages an hour, putting them at significant risk of premature death,'' Professor Willson said.

Those with 15 blockages an hour were three times more likely to die from heart disease, stroke or in a motor vehicle accident.

Clinic patient Mark Groves has suffered from sleeping difficulties in the past and said it was not a risk he wanted to take.

''Being hooked up tells me whether there's a problem or not so I can get the appropriate treatment,'' Mr Groves said.

Australian National University professor Kerry Jacobs has been using a breathing device for three years and said he had seen a remarkable transformation.

''In terms of clarity of mind, the change has been amazing. In terms of my productivity and my ability to think and engage, I soar,'' he said.

Bright light sources are also to blame for our lack of sleep, according to Dr Harrington, who said we sleep an average of two hours a night less than our grandparents. ''We've got a thing called melatonin, which is our sleep hormone. As soon as it detects bright light, it disappears.

''Unless we've got enough melatonin in our system or our brain, we're going to find it very hard to have consolidated sleep,'' she said. ''We're at the same stage with sleep we were with food and exercise in the late 1960s and early 1970s.''