Age-Specific TSH Reference Ranges

A physiological rise in TSH with age has been documented in multiple large cohorts in the USA, Japan, and China. Age-related structural and functional changes in thyroid tissue in older women — including reduced follicle size, increased fibrosis, and abnormal autoimmunity — collectively blunt the impact of TSH variation on fetal growth. Younger women have more vigorous basal metabolic rates and greater sensitivity to thyroid hormone fluctuations than older women. Applying a fixed TSH reference range across age groups overestimates the prevalence of subclinical hypothyroidism in older individuals.