There is little or no relation between how much sleep people get at night and how tired they feel, say researchers. "The length of sleep is not a good measurement to analyse whether we get enough sleep or not," Torbjoern Aakerstedt told AFP of the studies conducted at the Stress Research Institute of Stockholm University.
"It's genetically conditioned and dependent on age and health," he said.
Aakerstedt's team has conducted three different studies, one of which investigated the sleep patterns of nearly 6,000 individuals.
The research suggests that the number of hours slept is of much less importance in determining how a person functions throughout the day.
"If you feel fine and dynamic during the day, you've probably slept enough," said Aakerstedt.
The research, to be published later this year, found the average number of hours slept during a working week is six hours 55 minutes, with an extra hour's sleep during holidays.
The researcher said that 20-year-olds should sleep eight hours on average, whilst 60-year-olds require only six.
"But there is no general average," Aakerstedt added. "Twenty-year-olds can sleep even more, but still be tired during the day" as their brain is still developing.
Yet, although more sleep does not mean more energy, no one should sleep too little, as it affects one's health, he said.
Too little sleep can result in a weak immune system, type 2 diabetes, heart disease, weight gain, workplace incidents and traffic accidents.