When you've had a week's worth of lousy sleep, there are few things more tantalizing than knowing that come Saturday morning, you can sleep in for a while.

It's psychological, sure, something to get us through the last bit of the week, but it turns out that sleeping in may also have some serious health benefits.

At least that's the result of a study published in the Journal of Sleep Research that used 13 years worth of data from nearly 40,000 participants.

Weekend sleep warriors

In 1997, thousands of Swedes completed a 36-page survey as part of a fundraiser for the Swedish Cancer Society. Researchers tracked the mortality rates of 38,015 people over the next 13 years. Between 1997 and 2010, 3,234 of the participants died, most due to heart disease or cancer.

The researchers of the sleep study grouped participants according to their self-reported sleep duration. Those the study deemed short sleepers slept for fewer than five hours a week night, medium sleepers got the recommended seven hours of winks and long sleepers snoozed for nine or more hours. Researchers then divided these groups into narrower groups based on their weekend sleeping habits. For instance, short-short sleepers continued their five-hours-or-less sleeping patterns all week, while long-long sleepers did nine or more hours every night.

These two groups, the short-short and long-long sleepers, both faced increased mortality rates. The study found that the short-medium sleepers, meaning those who slept too little during week but got a solid seven hours on the weekends had a mortality rate that was in line with the average.

"The results imply that short (weekday) sleep is not a risk factor for mortality if it is combined with a medium or long weekend sleep," the authors of the study wrote.

Researchers attempted to account for the various things that can influence sleep patterns, including age, gender, body mass index, use of sleep aids, alcohol and exercise.

Age did play a role in the findings. Participants in their late teens and early 20s slept for an average of seven hours during the week but around 8.5 on days off. Those over 65 mostly slept fewer than seven hours every night. The latter group didn't show a tip in mortality rates one way or another.

It's important to emphasize that this was not an experiment and that the study cannot explain why those with more extreme sleep patterns had a higher mortality rate.

Torbjorn Akerstedt, director of the Stress Research Institute at Stockholm University and lead author of the study, stressed to The Washington Post that the conclusions the study draws are only "tentative."

So it might be best to just get a few more hours of sleep during weeknights and be a medium-medium sleeper.

Why you should sleep in on the weekends
Even if you're not getting all the sleep you need during the week, an extra hour or two on the weekends can make a difference in your life span.