Magnitude and Predictors of Subclinical Hypothyroidism in Individuals With Impaired Glucose Tolerance

TL;DR

This study found that subclinical hypothyroidism is common in people with impaired glucose tolerance but often resolves on its own without treatment.

Contribution

The study demonstrates that subclinical hypothyroidism in individuals with impaired glucose tolerance is transient and does not require thyroxine therapy.

Findings

12.2% of individuals with impaired glucose tolerance had subclinical hypothyroidism at baseline.

Most individuals with subclinical hypothyroidism reverted to normal thyroid function within a year without treatment.

There was no significant change in mean TSH levels over time.

Abstract

Background: The screening for thyroid function abnormalities in asymptomatic individuals remains a topic of debate. The impact of subclinical hypothyroidism (SCH) on glucose metabolism has been less extensively researched. Our study aimed to assess the feasibility of thyroid-stimulating hormone (TSH)-based screening and evaluate the prevalence of SCH among individuals with impaired glucose tolerance (IGT) in a community-based setting.

Methodology: We performed a longitudinal study in individuals with IGT by measuring clinical parameters and TSH at baseline and follow-up measurements at 6 and 12 months.

Results: We included 148 participants with IGT. The baseline mean HbA1c of the participants was 6.0% ± 0.2%, and the TSH level was 3.2 ± 2.1 µIU/mL. In the study, we found that 18 (12.2%) individuals with IGT had baseline TSH values in the SCH range (TSH 5-10 µIU/mL). Individuals with IGT who also had a TSH abnormality had significantly lower HbA1c levels as compared to those who were euthyroid (5.9% ± 0.2% vs. 6.1% ± 0.2%, P < 0.008). Other measurements were similar between the two groups. There was a significant decline in mean HbA1c levels on follow-up (baseline HbA1c 6.1% ± 0.2% vs. follow-up HbA1c 5.4% ± 0.7%; P < 0.001). One year later, 14 individuals (87.5%) with SCH reverted to normal TSH levels without specific thyroxine therapy, while 17 individuals (15.8%) who were initially euthyroid developed TSH elevations into the SCH range, suggesting dynamic fluctuations in TSH levels among individuals. There was, however, no change in mean TSH levels on follow-up (baseline 3.2 ± 1.8 µIU/mL vs. follow-up 2.9 ± 2.3 µIU/mL; P = 0.22). The overall prevalence of SCH at baseline and follow-up was similar (16, 13.2%, vs. 18, 14.9%; P = 0.855).

Conclusions: The study highlights that SCH is a transient condition among individuals with IGT. The majority of these individuals reverted to normal thyroid function after one year without requiring thyroid hormone therapy, underscoring the unstable nature of SCH.

Figures