DARTMOUTH:   Selenium has a crucial role in controlling the effects of thyroid hormone on fat metabolism, report researchers at Dartmouth Medical School.

A new study published in the July 15, 1996 issue of The Journal of Clinical Investigation, underscores the importance of nutrition in thyroid hormone function. The researchers report that the key enzyme responsible for activating thyroid hormone in the brain and in brown fat, a heat-producing type of fat tissue, contains the rare amino acid selenocysteine that is formed in the body using dietary selenium. High amounts of selenium are present in such foods as beef, bread, poultry and seafood.

Thyroid hormone, which is produced in the thyroid gland using iodine, another nutritional element, influences several important body functions. These include fat metabolism in adults, and energy production and brain development in the fetus and newborn. In addition, patients with thyroid diseases often have difficulties with memory and mood changes.

However, before thyroid hormone can exert its effects, it must be activated. This occurs when specialized enzymes in various tissues remove an iodine atom from the hormone. Selenium appears to play an essential role in this process because of its unique ability to act as a strong catalyst and spur the activating reaction.

Although selenium had previously been shown to help activate thyroid hormone in the liver and kidney, its role in the function of the brain and brown fat enzyme had been controversial.