Every year, some people receive a unique prescription from their doctor: light therapy. Instead of medicine, they are advised to use specific light to improve their mood. This treatment is often recommended for those who suffer from seasonal affective disorder (SAD), a type of depression that occurs at certain times of the year, mostly in fall and winter when days are short. SAD affects around 1% of people and causes serious symptoms such as sadness, loss of interest in activities, fatigue, sleep problems, weight changes, and sometimes suicidal thoughts.
Scientists believe that SAD is linked to changes in our biological clock, called circadian rhythms. Light enters the eyes and sends signals to the brain’s suprachiasmatic nucleus, which controls daily rhythms like sleep, hormone production, and body temperature. In most people, melatonin, a sleep hormone, is released at the same time each night. But for people with SAD, this hormone may be released longer or at a different time, causing mood problems. Another idea is that their eyes do not adjust well to the lower light levels in winter.
Light therapy helps by exposing the patient to strong artificial light, simulating sunlight, and helping reset the biological clock. Understanding SAD can explain why humans, like animals, experience seasonal changes in behavior, showing how sunlight and our brain chemistry influence mood and daily rhythms.
Vocabulary:
• Prescription (noun): A doctor’s written advice for treatment or medicine.
• Therapy (noun): Treatment to improve health or mood.
• Cascade (noun): A series of events that happen one after another.
• Inhabitants (noun): People or animals living in a certain place.
• Hibernation (noun): A period when animals sleep through winter.
• Affect (verb): To influence or change something.
• Disorder (noun): A medical condition affecting the body or mind.
• Fatigue (noun): Extreme tiredness.
• Circadian rhythms (noun): The body’s natural daily cycles.
• Melatonin (noun): A hormone that makes you feel sleepy.
• Biological clock (noun): Internal system controlling body functions daily.
Source: TED-ed