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Correlation of Thyroid-Stimulating Hormone levels and Risk of Developing Type 2 Diabetes

Increasing TSH levels rather than baseline TSH levels may elevate the risk of developing type 2 diabetes.

Prior studies have validated that thyroid function influences glucose metabolism. However, the relationship between thyroid stimulating hormone levels and the risk of developing T2DM is not clear. In addition, no longitudinal studies have been performed to determine this association.

Researcher Ji-Eun Jun, MD, and his partners from the Samsung Medical Center located in Korea studied euthyroid patients without diagnosed T2DM. They were interested in finding the relationship between changes in TSH levels and incidence of type-2 diabetes. Normal thyroid levels were utilized to define euthyroid in participants. These levels were specifically noted as normal total thyroxine (4.7-12.5 ng/dL), free thyroxine (0.78-1.85 ng/dL) and normal triiodothyronine (76-190 ng/dL), and normal TSH level (0.4-4.2 pIU/L).

Researchers measured changes in TSH as a ratio, which was calculated at the end of follow-up with baseline TSH levels. The study found that there were 726 incident cases of T2DM during 86,010 person-years of follow-up. There was also a significantly increased risk for incident diabetes with a higher TSH ratio (HR = 1.1; 95% CI, 1.02-1.18; P= 0.011). This was observed after adjustments were made for baseline HbA1c, FPG, age, gender, BMI, triglycerides, HDL, and LDL cholesterol. Researchers also noted a greater risk for incident T2DM in subjects with the highest TSH ratio (HR = 1.39; 95% CI, 1.16-1.66; P for trend < 0.001).

The authors claimed that euthyroid status was maintained in nearly all subjects in the highest tertile of TSH ratio, which was approximately 83% of participants. It was also noted that baseline TSH or tertiles was not associated with the risk for incident T2DM. Overall, investigators claim that the study displays incremental TSH, instead of baseline TSH, may be considered as an additional risk factor for incident of T2DM. Furthermore, this risk is evident even in the instance where subjects exhibit euthyroidism.

Practice Pearls:

  • Incremental changes in the TSH levels rather than baseline TSH level itself can be an additional risk factor for the incident of T2DM
  • Even when subjects display a euthyroid state, the risk of incident T2DM is present with increasing TSH levels regardless of baseline TSH levels

Jun J, et al. Abstract #88. Presented at: 51st EASD Annual Meeting; Sept. 14-18, 2015; Stockholm.