Answer :

Goitre is a disease caused by the deficiency of iodine and is characterised by the enlargement of thyroid gland present in our neck. It is an endemic disease and mostly affect people living in hilly areas.
It is less common in people living in coastal areas, since their diet mainly consist of sea food, which is a rich source of iodine. Iodine is also present in the soil of coastal areas. All these factors are responsible why this disease is rare in coastal areas