A new study finds mood cycles hit their lowest point around 5 in the morning and their highest around 5 in the evening.

Americans have long been divided over adopting permanent standard versus permanent daylight saving time. But support for permanent standard time grew dramatically between 2021 and 2024.

"Teens are chronically sleep deprived," says Alison Kole. "And we need to start talking about why that is."

Most teens aren’t getting enough sleep, leading to poorer academic performance. Early school start times combined with natural changes in hormones and the circadian rhythm could be to blame.

Grizzly bears' circadian rhythm keeps on ticking, even when they are in hibernation, a new study shows.

Synchronizing your daily activities to your circadian rhythm could help you improve your performance on a variety of cognitive tasks − and even influence diagnosis of cognitive disorders.

Why plants’ oscillating genes matter for humans.

Time of day may be important for how effective the COVID-19 vaccine is. A new study suggests middle of the day may be be best.

Early birds are more likely to follow guidelines for using CPAP machines for sleep apnea, using them for longer periods at night.

Sunflowers' circadian clocks control how individual florets open in concentric rings to maximize visits from pollinators.