The natural ""cycle"" of darkness to daylight amazingly coordinates your body's biologic and ""circadian"" rhythms and your sleep-wake cycle...But, the light-dark cycle doesn't always go as it should in some children and adults with ADHD or attention deficit hyperactivity disorder, according to [UAB Professor of Psychiatry, Dr. Rachel Fargason]. Her team's research revealed ADHD's strongly linked to... delayed ""circadian rhythms"" and delayed circadian rhythm sleep disorder.