Chronic iodine excess and aging act synergistically to elevate serum thyrotropin (TSH) levels over a 20-year period.
TSH elevations induced by iodine excess appear irreversible; reducing iodine intake to sufficient or even deficient levels does not restore TSH to baseline.
In non-autoimmune individuals, alleviating iodine excess actually promotes the degree of aging-related TSH elevation, while persistent excess maintains high absolute TSH but blunts the rate of increase.
Long-term iodine excess is significantly associated with reduced central thyroid hormone sensitivity and an increased prevalence of subclinical hypothyroidism (SCH).
