ABSTRACT
Serum thyroid stimulating hormone (TSH) levels increase with age. This elevation has been associated with better outcomes in very elderly subjects; however, little is known about the relationship between TSH below the lower limit of the reference range and health-related outcomes. Here, we investigated the association between cognitive impairment or depressive symptoms and low-normal serum TSH (<1.0 µIU/mL, in the reference range) in elderly subjects and whether the use of methimazole in subjects without dementia but with low-normal TSH could affect cognition or depressive symptoms. From 293 healthy adults ≥65 years old with normal TSH included in the sectional phase, only subjects without dementia were prospectively analyzed: 1) TSH ≥1.0 µIU/mL (observation; untreated); 2) TSH <1.0 µIU/mL (observation; untreated); and 3) TSH <1.0 µIU/mL (methimazole therapy). Cognition was assessed, using the Mini Mental State Examination (MMSE) and depressive symptoms (at MMSE ≥ 13) by the Geriatric Depression Scale (GDS). Age >80 years was the sole independent factor associated with dementia (OR=2.89; confidence interval [CI] 1.72-4.86; p<0.01). Prospectively, 93 completed follow-up, with 7.5% (7) receiving methimazole intervention. Untreated subjects with lower TSH showed the greatest declines in MMSE scores during follow-up that was not observed in those with serum TSH ≥1.0 µIU/mL. Lower MMSE score reductions were associated with elderly subjects receiving methimazole. There were no significant changes in depressive symptoms and GDS scores among those with serum TSH <1.0 µIU/mL. In this study, low-normal TSH was not associated with higher prevalence of dementia. However, in elderly subjects without dementia, low TSH was associated with worsening cognition.
