For the study, researchers analyzed data from the National Health and Nutrition Examination Survey2, which included over 11,000 participants, ages 6 and up. For seven days, the participants wore accelerometers, which track movement and, subsequently, sleep.

Based on their findings, it appears that people’s sleeping patterns, namely sleep duration (or how long they sleep), form a U-shape, with sleep decreasing as we approach middle age and increasing following middle age.

Specifically, they found, 40 appears to be the age that Americans are getting the least sleep on average. And at around age 50, sleep duration starts to increase again.