April 11, 2000
Question: Is there a difference between hypothyroidism and hypometabolism, or does one result form the other?

Dr. Lowe: Yes, hypothyroidism and hypometabolism are different phenomena. Hypothyroidism is a lower-than-normal level of thyroid hormones in the circulating blood due to an underactive thyroid gland. The lower-than-normal blood thyroid hormone levels result in too few thyroid hormones reaching the body's cells. As a result, the metabolism of the cells becomes slower. When the metabolic rate becomes abnormally slow, we call the condition "hypo-metabolism" ("hypo" means under or low.) When metabolism slows far enough, the person develops characteristic symptoms. We say that the person is hypometabolic. So, hypothyroidism is a cause of hypometabolism.

However, hypothyroidism is not the only cause of hypometabolism; a patient's metabolism can be slower than normal for other reasons. Metabolism also becomes slower than normal in people who have normal blood thyroid hormone levels but who also have cellular resistance to thyroid hormone. The response of these people’s cells to thyroid hormone is blunted. Also, metabolism becomes abnormally slow in sedentary people, and in those who have certain nutritional deficiencies. Both a sedentary lifestyle and nutritional deficiencies are extremely common. In fact, these causes of hypometabolism are probably more common than hypothyroidism or cellular thyroid hormone resistance.