Fairly small, the gland is only about a quarter of an inch long in an adult and may range from a white to pinkish gray color. The pineal gland seems to play an important role in human sexual development. The large quantity of melatonin it secretes during early childhood is believed to somehow delay or slow a child's sexual development. Melatonin production in humans is greatest at night, and injection of the hormone makes people sleepy. Conditions that affect the pineal gland Both benign and cancerous tumors may develop on the pineal gland.
Doctors believe the depression develops because people are exposed to less sunlight during winter.