Goitre, conceptual image. Patient holding her neck due to goitre. This is an enlargement of the thyroid gland (coloured) in the neck, usually due to a deficiency of the essential mineral iodine. A strip of ultrasound scans of the area is at lower right. The thyroid gland is responsible for producing iodine-containing hormones that regulate the metabolism. If there is a deficiency of iodine the gland swells and the metabolism is disrupted, leading to weight gain, fatigue, slowed heart rate and depression. Iodine supplements can reverse the condition.