According to a May 2023 study published in Chronobiology International, night owls — people who go to bed later and wake up later — possibly die earlier than those who operate during the earlier portions of the day. That mainly because those who are up late are more at risk of developing unhealthy habits, Finnish Institute of Occupational Health researcher Christer Hublin told CNN.

“The increased risk of mortality associated with being a clearly ‘evening’ person appears to be mainly accounted for by a larger consumption of tobacco and alcohol,” Hublin said in a statement. “This is compared to those who are clearly ‘morning’ persons.’”

Hublin’s study followed roughly 24,000 twins from 1981 to 2018 in order to record possible causes of health-related behaviors. Roughly 10% of twins involved in the study said they were definitely evening people, while 33% said they somewhat preferred staying up late.

The study accounted for each twin’s education level, alcohol consumption, use of smoke products, body mass and sleep duration to compare and contrast the lifestyles of night owls to morning people. According to the results, night owls are at a 9% higher risk of an early death than morning people.

“We have known for a long time that those who have an evening type preference are more likely to be heavier drinkers, have alcohol use disorder and are also more likely to use other substances including tobacco,” Dr. Bhanu Prakash Kolla, a sleep medicine specialist, told CNN.

While alcohol use and smoking may play a role in the 9% risk hike, they do not tell the whole story.

“Other possible causes that come to mind include those who are evening types will likely need to wake up early for work/school therefore end up getting less sleep and the sleep deprivation can increase risk,” Dr. Kolla said.