Chronic Iodine Excess and Aging Synergistically Impact Thyrotropin Elevation: A Prospective 20-Year Follow-Up Study in China
Authors' conclusion
Elevated TSH levels induced by chronic iodine excess cannot be downregulated by reducing iodine intake. In nonautoimmune contexts, an interaction effect between iodine status and aging synergistically modulates the TSH rising degree. Iodine excess contributes to mild SCH and is correlated with high baseline TSH levels.
Study context
- Population
- Euthyroid participants from three communities in North China, cohort started 1999
- Participants
- 1,176 participants
- Exposure
- Iodine-excess transition groups vs continuous iodine sufficiency
- SI-SIn = 261reference
- EI-DIn = 145
- Excess to iodine sufficiency (EI-SI)n = 530
- EI-EIn = 240
- Outcome
- TSH levels (independent and interactive effects of iodine-excess transition and aging)
- Follow-up
- 20-year follow-up
Methodological details20-year follow-up, three communities in North China
- 20-year follow-up
- Three communities in North China
Main finding
As reported in the abstract
P < 0.05
Observational data: associations, not effects.
Further findings
Mild SCH (TSH <10.0 mU/L) prevalence, antibody-negative · After 20 years — EI-DI, EI-SI, EI-EI vs SI-SI · increased prevalence in iodine-excess groups
P < 0.05
TSH rising degree, antibody-negative · 20 years — between EI-EI and SI-SI, EI-DI, EI-SI · lowest TSH rise with EI-EI
P < 0.05
Percent rise SI-SI 24.57% · EI-DI 24.56% · EI-SI 37.52% · EI-EI 14.18%
Mild subclinical hypothyroidism (SCH) (TSH <10.0 mU/L) prevalence, antibody-negative · After 20 years
- Reduced central thyroid hormone sensitivity in iodine-excess groups vs SI-SI
Baseline TSH (1999-2004)
- Baseline median TSH positively associated with initial urinary iodine concentrations (UIC)
Thyroid antibody–positive participants
- No significant aging × iodine interaction; greater SCH prevalence, notably high severe SCH under persistent iodine excess
Original publication
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