Seasonal affective disorder (SAD), also called seasonal depression, is related to changes in the seasons and occurs each year around the same time. There are two types of SAD: winter-pattern and summer-pattern. Summer-pattern SAD occurs in around 10 percent of cases.
Winter SAD may lead to an overproduction of melatonin, while summer SAD may result in lower melatonin levels. Further research is needed to determine how melatonin may impact symptoms of seasonal depression.