National trends in sleep sufficiency and sleep time among adolescents, including the late-COVID-19 pandemic, 2009-2022: A nationally representative serial study in South Korea.

• Over the 14-year period, both sleep duration among South Korean adolescents demonstrated a consistent downward trend. • A noteworthy decrease in sleep sufficiency was observed during the pandemic compared to the pre-COVID-19 period (2009–2019). • Regardless of the pandemic period, there was a decrease in sleep time, with no difference in the slopes of these decreases. • It is necessary for the society to solve not only the downward trend in sleep sufficiency but tackle the underlying cause. [ABSTRACT FROM AUTHOR]