E-news: Treatment of sub-clinical hypothyroidism doesn't improve cognition in elderly

Parle et al report a small but exceptionally important randomised controlled study of thyroxine supplementation in an elderly cohort with subclinical hypothyroidism, showing no improvement in cognitive function with normalisation of TSH.

Subclinical hypothyroidism and cognitive dysfunction are both common in the elderly and have been linked. This double-blind placebo-controlled randomised controlled trial was conducted to determine whether administration of T4 replacement to achieve biochemical euthyroidism improves cognitive function.

Ninety-four subjects aged 65 years and over (57 females, 37 males) with SCH were recruited. T4 or placebo was given at an initial dosage of one tablet of either placebo or 25 µg T4 per day for 12 months. Thyroid function tests were performed at 8-weekly intervals with dosage adjusted in one-tablet increments to achieve TSH within the reference range for subjects in treatment arm.

Cognitive function was tested at baseline and six and 12 months, using the mini-mental state examination, Middlesex elderly assessment of mental state, and trail-making A and  B. Linear mixed-model analysis demonstrated no significant changes in any of the measures of cognitive function over time and no between-group difference in cognitive scores at six and 12 months.

This RCT provides no evidence for treating elderly subjects with SCH with T4 replacement therapy to improve cognitive function.