People tend to have their worst sleep between their early thirties and their fifties, according to a new study published in the journal Nature Communications. Researchers from multiple institutions collected sleep data from over 700,000 people from 63 countries. Overall, they observed that the average amount of sleep among all people was 7.01 hours per night, on the lower end of the recommended amount of sleep. Younger participants, around age 19, slept the most, but then sleep duration started to drop. Among people in their early thirties to those in their fifties, sleep duration was the shortest. Adults older than that had slightly longer nights of sleep. Why people 30 to 50 have the worst sleep is unclear, although work and child responsibilities likely play a role.