Evidence regarding thyroid function changes with ageing remains inconsistent and the implications of potential changes are unclear. We aimed to investigate ageing-related thyroid function changes and their associations with mortality.

The association of thyroid peroxidase antibodies (TPOAb) status with cardiovascular disease (CVD) risk, independent of thyroid function, remains unclear. We aimed to determine whether positive TPOAb is associated with increased CVD risk, overall and among individuals with subclinical hypothyroidism.

Reference intervals of thyroid-stimulating hormone (TSH) and free thyroxine (FT4) are statistically defined by the 2·5-97·5th percentiles, without accounting for potential risk of clinical outcomes. We aimed to define the optimal healthy ranges of TSH and FT4 based on the risk of cardiovascular disease and mortality.