Sub-clinical hypothyroidism in diabetes and effect of metformin on thyroid stimulating hormone

Patients with type 2 diabetes mellitus (DM) are associated with elevated thyroid stimulating hormone (TSH)level. Metformin is considered as standard therapy in type 2 DM and it alters TSH levels. Objective: To see the effect of metformin treatment on thyroid function in patients with type 2 diabetes mellitus. Design: Interventional Clinical Trial using convenience sampling Place and Study Duration:The study was conducted in Dallah Hospital, Riyadh, Kingdom of Saudia Arabia. It lasted for an year (from April 2014 to June 2015). Material and Methods: Two hundred and seventy one patients with type 2 DM were given metformin 2000 mg/day for approximately 24 weeks. Th e thyroid function [TSH, free thyroxin (FT4) and total thyroxin (TT 4)] done at baseline, after 12 weeks and 24 weeks of metformin therapy. Two groups, the euthyroid group and SHT group were analyzed and compared. Results: Among 271 patients, 15.5% (42) were classified in SHT group, whereas 84.5% (229) in euthyroid group. There were no significant differences of age and lipid levels between two groups whereas the high BMI, female gender, high FBS and HbA1c were associated with SHT group.Th e mean baseline TSH was 2.94+2.36 mIU/L in all subjects, 7.54+2.69 mIU in SHT group whereas 2.10+0.83 in euthyroid group. Th ere was significant reduction in TSH level noted in SHT group aft er 3 months(p=0.017) and 6 months(p<0.001) of metformin therapy.The mean baseline TT 4 was 9.13+1.59 in all subjects, 8.57+2.10 in SHT group whereas 9.24+1.40 in euthyroid group. Th e mean baseline FT4 was 1.08+0.24 in all subjects, 1.07+0.35 in SHT group whereas 1.08+0.22 in euthyroid group. Conclusions: The study revealed close association of SHT with type 2 DM. The TSH lowering effect of metformin therapy only evident with SHT. There was no significant change seen in FT4 and TT 4 levels. (author)