Back in 1997, a number of Swedish people completed a survey for the Swedish Cancer Society and researchers tracked the mortality rates of 38,015 people during the next 13 years. Between 1997 and 2010, 3,234 of the participants died, most due to heart diseases or cancer.
During the research, scientists grouped the participants based on their sleep duration: short sleepers slept fewer than five hours a week night, medium sleepers got the recommended seven hours of sleep and long sleepers slept nine or more hours. Then the researchers divided these groups into narrower groups based on people’s weekend sleeping habits: short-short sleepers had their five-hours-or-less sleeping patterns all week, while long-long sleepers slept nine or more hours each night. These two groups both faced increased mortality rates.
The study found that the short-medium sleepers – who slept too little during week but got seven hours on the weekends – had a mortality rate that was in line with the average.
According to the authors, these results show that short weekday sleep does not mean a risk factor for mortality if it is combined with a medium or long weekend sleep.
Researchers studied various things that can influence sleep patterns, such as age, gender, BMI, use of sleep aids, alcohol and exercise. They say that age plays an important role in their findings: participants in their late teens and early 20s slept about seven hours during the week, but about 8.5 hours on their days off, while people over 65 mostly slept fewer than seven hours each night.
It’s important to emphasize that this study was not a scientific experiment and it cannot explain why those with extreme sleep patterns had a higher mortality rate.
The whole article can be read here.