How does the weather affect mood?

Most people are happier and more optimistic when there is sunshine compared to rain and clouds. This is also seen through Twitter posts, altruistic behavior, restaurant tipping, depression and suicide. Sunshine causes the brain to increase a neurotransmitter called serotonin. Serotonin relays signals between neurons in the brain that regulate happiness, anxiety, and other facets of mood, as well as bowel function, clotting, bone density, and sexual function. Low levels of serotonin, which may be caused by lack of sunshine among many other causes, leads to less happiness, higher anxiety, depression, and difficulty sleeping. Conversely, darkness or darker lighting causes the body to produce a hormone called melatonin which is produced by the pineal gland. Melatonin is often called the sleep hormone as it influences your circadian rhythm. A rise in melatonin levels tells the body that it is time to sleep. Further, melatonin binds to brain receptors to reduce nerve activity and dopamine levels that are trying to keep the body alert and awake