Two out of three people in Britain suffer from insomnia, mostly linked to stress and personal worries, a new survey has revealed.

Women are more likely to suffer from sleepless nights than men, according to the survey commissioned by life sciences group Rhone-Poulenc Rorer.

The reasons why many people lie awake at night include health concerns and relationship difficulties.

Marital breakdown

The survey, which polled people in five European countries, found severe insomniacs had often experienced marital breakdowns or were single parents.

Insomnia was a particular problem in Sweden, where three quarters of the population were sufferers. Other countries polled were Germany, Ireland and Belgium.

Rhone Poulenc spokeswoman Karen Scott said: "We chose the five countries to give a good cross-section of insomnia suffering in Nordic European countries with distinct cultures."

The study also showed that in Britain and Sweden, severe sufferers - those with difficulty going to sleep and waking frequently during the night - were more likely to be in the 25 to 34 age bracket.

According to the poll, the Germans had the lowest number of insomniacs - 45% of the population were affected.

School performance

A US study has found that some children who perform poorly at school may have a sleep disorder that leaves them fatigued.

Researchers found one in five under-achieving youngsters showed signs of sleep apnea, a condition in which breathing stops briefly during sleep, disturbing the suffer.

The percentage of children with bad grades found to have sleep apnea symptoms was 6-9 times higher than that found in the overall child population.

Sleep apnea can be treated with surgery. Those children who underwent treatment improved their performance at school.