Age takes a toll on our internal clocks. Universal Stopping Point Photography/Getty Images hide caption

toggle caption Universal Stopping Point Photography/Getty Images

Gulping down coffee to stay awake at night delays the body's natural surge of the sleep hormone melatonin. Hayato D./Flickr hide caption

toggle caption Hayato D./Flickr

All in the name of science: Volunteers hike in Colorado during their one-week hiatus from electrical lighting. Courtesy of Kenneth Wright hide caption

toggle caption Courtesy of Kenneth Wright
Anton-Marlot/iStockphoto.com

NPR thanks our sponsors

Become an NPR sponsor