Which hormone is hypothesized to play a role in Seasonal Affective Disorder (SAD)?

• A. Serotonin
• B. Dopamine
• C. Melatonin
• D. Cortisol

Answer: (C)

Melatonin is the hormone that is closely linked to the regulation of sleep-wake cycles and is influenced by the amount of light exposure, which can fluctuate with the seasons. In individuals who experience Seasonal Affective Disorder (SAD), changes in daylight exposure during different seasons can disrupt normal melatonin production. During the winter months, when days are shorter and light levels are lower, melatonin production might increase, leading to symptoms such as depression, fatigue, and changes in sleep patterns often observed in SAD.

In this context, melatonin's role as a regulator of circadian rhythms ties it directly to the seasonal patterns of mood changes associated with SAD. Other hormones, like serotonin and dopamine, are also involved in mood regulation but are not as directly implicated in the seasonal changes that characterize this disorder. Cortisol, a stress hormone, can affect mood as well but does not have the same seasonal correlation as melatonin does in SAD cases. Thus, melatonin is critically relevant to understanding the biological underpinnings of Seasonal Affective Disorder.