hormone (collectively T3 and T4), produced by the thyroid gland, is
the single most important hormone influencing the rate of cellular
metabolism and body heat production.
conditions of excess thyroid hormone production (hyperthyroidism),
an individual's basal metabolic rate (BMR), heat production, and oxygen
consumption increase, and the individual tends to lose weight and
become heat-intolerant and irritable.
hypothyroid individuals become mentally and physically sluggish obese,
and are cold-intolerant because of their low BMR.