Lack of enough sleep can lead to serious health problems. Scientists have found out that people under the age of 65 who sleep for five or less hours a day are at an increased risk of premature death compared to those who sleep six or seven hours per day.

However, the effect of not sleeping enough during the working days may be at least partially offset during the weekend. A large-scale study that included 38 000 people has proven that people who sleep until later on Saturdays and Sundays are not at risk from the same health problems. There is also no risk of early death.

"The duration of sleep is important for longevity," said Thorbjorn Akersted of the Stress Research Institute in Sweden, quoted by The Guardian.

The study considered factors such as sex, weight, physical activity, smoking, stress at work. The results show that among people sleeping 5 hours a day, there is a 65% higher mortality rate. However, those who catch up with sleep during the weekends and for that period sleep for 8 hours or more per day do not have an increased risk of premature death.

Curiously, after the age of 65, there is no relationship between sleep duration and mortality. Researchers say that older people need less sleep and they also sleep more during the week.