Drinking coffee is refreshing and refreshing. It doesn't work for night owls.

Drinking coffee can be refreshing and refreshing, but it can also lead to sleepless nights. Caffeine only affects the sleep of lark people who are used to going to bed early and getting up early, but does not interfere with the sleep of night owls who like to stay up late, a new US study has found.

In the new study, Stanford University researchers asked 50 college students to record their caffeine intake during the week and their sleep / wakefulness time. Students wear a device on their wrists that can detect their physical activity, which can record the participants' wakefulness during sleep at night. The researchers also measured the level of caffeine in the saliva of each student during the week. It was found that "lark" people were more likely to wake up at night and interrupt sleep after consuming caffeine during the day. The new study found for the first time a link between caffeine intake and "time type", the most alert or active time of day, the researchers said.

Jamie Zetzler, Ph.D., associate professor of psychiatry and behavioral science, who led the new study, said that most college students don't get enough sleep and can fall asleep no matter how much coffee they drink. But for lark people, the more caffeine they consume, the longer they stay awake during sleep at night. This is not reflected in the "night owl" type. The next step in the study will be to conduct the same study on non-college students to determine whether it is common for caffeine to interfere with sleep only in the "lark" type.

Dr. Zetzler said that everyone's metabolism of caffeine is different. Some people can metabolize caffeine in a few hours, and some people still have caffeine in their lunchtime coffee at night. Therefore, if you belong to the lark type, it is best not to eat too much caffeinated drinks such as coffee or tea after noon.