Thyroid hormones (T3 and T4) affect almost all metabolic processes in the body.
Carbohydrate Metabolism
Thyroid hormones accelerate glucose absorption, glycogen synthesis and glycolysis; they potentiate insulin action.
Fat Metabolism
They affect fatty acid mobilisation, oxidation and cholesterol synthesis. Cholesterol levels rise in hypothyroidism and fall in hyperthyroidism.
Protein Metabolism
In physiological amounts, they increase protein synthesis; in excess, they cause protein breakdown (catabolism).
Calcium and Phosphorus Metabolism
They affect bone turnover; prolonged hyperthyroidism may increase the risk of osteoporosis.
Interaction with Other Hormones
They modulate the effectiveness of growth hormone, insulin, adrenal cortex hormones and catecholamines. Thyroid hormone deficiency adversely affects growth hormone secretion.