Should thyroid‐stimulating hormone goals be reviewed in patients with Type 1 diabetes mellitus? Results from The Brazilian Type 1 Diabetes Study Group

Aims To investigate if thyroid‐stimulating hormone ( TSH ) levels are associated with any differences in glycaemic control or diabetes‐related complications in individuals with Type 1 diabetes. Methods This observational, cross‐sectional and multicentre study included patients with Type 1 diabetes for ≥ 5 years, with a recent TSH measurement and without a known previous thyroid disease. Patients were divided into three groups according to TSH levels: 0.4–2.5 mU/l; 2.5–4.4 mU/l; and ≥ 4.5 mU/l. Results We included 1205 individuals with a mean ± sd age of 23.8 ± 11.3 years. Seven patients had TSH levels <0.4 mU/l and were excluded from the comparison between groups. HbA 1c levels, systolic and diastolic blood pressure, LDL cholesterol and disease duration were similar in all groups ( P  =   0.893, P  =   0.548, P  =   0.461, P  =   0.575 and P  =   0.764, respectively). The rates of diabetic retinopathy and GFR < 60/mL/min/1.73 m 2 differed between groups ( P  =   0.006 and P  <   0.001, respectively) and were lower in those with lower TSH levels. Multivariate analysis confirmed these associations. The frequencies of retinopathy and GFR < 60 mL/min/1.73 m 2 were higher not only in patients with TSH ≥ 4.5 mU/l (odds ratio 1.878 and 2.271, respectively) but also in those with TSH levels of 2.5–4.4 mU/l (odds ratio 1.493 and 2.286, respectively), when compared with patients with TSH levels of 0.4–2.5 mU/l. Conclusions TSH levels of 0.4–2.5 mU/l are associated with a lower risk of diabetic retinopathy and renal failure in individuals with Type 1 diabetes, independently of glycaemic control and duration of the disease.