Not being able to get enough sleep at night may make you feel older, according to a study conducted by Stockholm University in Sweden. Leonie Balter, a sleep researcher at the university, led two studies that showed how sleep patterns affected both young and old people. In the first study, questionnaires were distributed to 479 individuals aged between 18 and 70 that helped analyze the quality of their sleep. Research found that those who never experienced insufficient sleep over 30 days had a subjective age of 5.81 years younger than their actual age. The findings also found that “for each additional day of insufficient sleep during the last 30 days, subjective age increased by 0.23 years". The second study saw 186 people sleeping in a lab, with participants sleeping for four hours the first two nights and nine hours the second two nights. Participants felt on average 4.44 years older after four hours of sleep, compared to feeling 0.24 years younger after nine hours of sleep.