Neuropsychological function and symptoms in subjects with subclinical hypothyroidism and the effect of thyroxine treatment

J Clin Endocrinol Metab. 2006 Jan;91(1):145-53. doi: 10.1210/jc.2005-1775. Epub 2005 Nov 1.


Objective: Our objective was to examine the relation between neuropsychological function and subclinical hypothyroidism (SHT), defined as serum TSH of 3.5-10.0 mIU/liter and normal serum free T4 and free T3 levels, and to study the effect of T4 supplementation.

Subjects: A total of 89 subjects (45 males) with SHT and 154 control subjects (72 males) were recruited from a general health survey (the fifth Tromsø study). Sixty-nine of those with SHT were included in a placebo-controlled, double-blind intervention study with T4 medication for 1 yr.

Main outcome measures: We used fourteen tests of cognitive function, Beck Depression Inventory, General Health Questionnaire, and a questionnaire on hypothyroid symptoms.

Results: The mean +/- sd serum TSH in the SHT and control group were 5.57 +/- 1.68 and 1.79 +/- 0.69 mIU/liter, respectively. There were no significant differences in cognitive function and hypothyroid symptoms between the two groups, but those with SHT scored significantly better than the controls on the GHQ-30. At the end of the intervention study, serum TSH in the T4 group (n = 36) and the placebo group (n = 33) were 1.52 +/- 1.51 and 5.42 +/- 1.96 mIU/liter, respectively. T4 substitution had no effect on any of the parameters measured.

Conclusion: In subjects with SHT where the serum TSH level is in the 3.5-10.0 mIU/liter range, there is no neuropsychological dysfunction, and compared with healthy controls, there is no difference in symptoms related to hypothyroidism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Cognition / physiology
  • Cohort Studies
  • Emotions / physiology
  • Female
  • Humans
  • Hypothyroidism / drug therapy*
  • Hypothyroidism / psychology*
  • Male
  • Middle Aged
  • Neuropsychological Tests
  • Norway
  • Regression Analysis
  • Surveys and Questionnaires
  • Thyrotropin / blood
  • Thyroxine / therapeutic use*


  • Thyrotropin
  • Thyroxine