Thyroid function in patients with selenium deficiency exhibits high free T4 to T3 ratio.
Level 4 - case-series / case-control
Retrospective case-series / case-control study with a small uncontrolled pre-post supplementation subgroup
PubMed 33446948 · doi:10.1297/cpe.30.19
What was done
A retrospective study evaluated thyroid function (TSH, free T4 [FT4], free T3 [FT3], and FT4/FT3 ratio) in 22 patients diagnosed with selenium deficiency compared to a control group. Thyroid hormone changes were also evaluated before and after selenium supplementation in a subset of 7 patients presenting with abnormal baseline thyroid hormone levels.
What was found
Among the 22 selenium-deficient patients, TSH was increased in 3 (14%), FT4 was increased in 5 (23%), and FT3 was decreased in 6 (27%). The FT4/FT3 ratio was significantly higher in patients with selenium deficiency compared to controls, with a positive correlation observed between the degree of selenium reduction and the FT4/FT3 ratio (exact values and p-values not reported in abstract). Following selenium supplementation in 7 patients with abnormal baseline thyroid levels, TSH, FT4, and the FT4/FT3 ratio significantly decreased, while FT3 levels significantly increased.
Why it matters
This study provides clinical evidence that selenium deficiency impairs peripheral T4-to-T3 conversion via reduced deiodinase activity, leading to a high FT4/FT3 ratio that corrects with selenium replacement.
Limits
The sample size is small (n=22 total, n=7 for supplementation), and the design is retrospective. The abstract does not report the size or characteristics of the control group, specific patient demographics, baseline hormone concentrations, or exact statistical effect sizes. The supplementation intervention was uncontrolled and non-randomized.
Cited by
- supports Selenium is vital for the enzymatic conversion of thyroid hormone T4 to T3.