Cognitive decline linked to low serum TSH

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  • Among nondemented elderly, low-normal serum thyroid stimulating hormone (TSH; <1.0 μIU/mL) was linked to cognitive decline.

Study design

  • Cross-sectional analysis of 293 healthy adults aged 65 y or older with normal TSH identified nondemented adults for follow-up (median, 16 mo): 95 with TSH ≥1.0 μIU/mL; 8 with TSH <1.0μIU/mL, untreated; and 7 with TSH <1.0 μIU/mL treated with methimazole.

Key results

  • Low-normal TSH was not associated with higher prevalence of dementia in the cross-sectional study.
  • Greatest declines on Mini Mental State Examination (MMSE) during follow-up were in untreated participants with TSH <1.0 μIU/mL; those receiving methimazole had less MMSE decline.
  • Depressive symptoms and Geriatric Depression Scale scores did not change during follow-up in participants with TSH <1.0 μIU/mL.


  • Small sample of nondemented elderly with TSH <1.0 μIU/mL; lack of randomization or blinding.

Why this matters

  • Serum TSH levels increase with age. This increase has been associated with better outcomes among very elderly, but little was known about the association between low-normal TSH and health-related outcomes.
  • Elderly without dementia and low TSH should be monitored for cognitive decline to allow early intervention, including methimazole treatment if appropriate. Larger, randomized studies should help to inform such decisions.