Even if you stop drinking at midnight, your ability to work may still be impaired until 4pm the next day, the British Psychological Society London conference was told yesterday.
Researchers said that while the bad effects of being drunk were well known, there had been less work done on how hangovers can impair abilities to do jobs.
A group of student volunteers aged between 18 and 24 were recruited to see how concentration and information processing were affected by a "night out". After measuring their responses before they went out, the students each drank between four and nine bottles of beer, recreating a "party session". The next day they underwent a series of tests.
This included matching numbers and symbols and adding together numbers heard on a tape. "These are tasks that require quite a high level of concentration," said Dr Stuart Anderson, lecturer in neuro-psychology at the University of Natal, South Africa. He found that 16 hours after stopping drinking the students were still experiencing the effects of a hangover - nausea, headache, fatigue, depression and dizziness. And they scored less well on the tests than those who had not drunk anything.
Dr Anderson said that people with a hangover reacted particularly badly to stressful situations where they had to think about two things at once. "These results have serious implications for anyone who drinks alcohol," said Dr Anderson. "Even when the students reported feeling sober, the hangover effects could still be seen in their test performance for hours after they stopped drinking.
"Would you like your appendix taken out by a surgeon who had had nine beers 12 hours earlier or be in a plane flown by a pilot with a hangover?"
He said that work productivity was likely to be less over the festive season, and he added: "It would be better to hold office parties on Friday to have the weekend off to recover by Monday."
1 Being on a diet can be a weight on the mind, with slimmers faring less well in mental tests than those who eat what they want, according to the Institute of Food Research.
Dr Mike Green, senior research psychologist, said that tests showed that it was not due to food deprivation or lowered glucose levels. People who were not allowed to eat for 24 hours had not shown the same results. Anxiety about losing weight meant dieters exhibited the same sort of signs as the clinically depressed. They also demonstrated poorer short-term memory and slower reaction times than those who did not think about what they ate.