Diabetes patients with euthyroid status, but with low- and high-normal serum TSH levels, are at increased all-cause and cardiovascular disease mortality risk, according to a study published in the journal Cardiovascular Diabetology.¹

Zhu et al examined data of patients with diabetes from the Third National Health and Nutrition Examination Survey database to determine the association between normal TSH levels and mortality, all-cause and cardiovascular, among euthyroid adults with diabetes. Out of the 2833 diabetics enrolled in NHANES III, 1830 were selected for the final analysis. The National Death Index records were used to determine mortality. The reference range for TSH in NHANES III was 0.39–4.60 mIU/L. Hence, based on the levels of TSH, the euthyroid patients were categorized into three groups as high-normal (2.09-4.60 mIU/L), medium-normal (1.30-2.09 mIU/L) and low-normal (0.39-1.30 mIU/L). The follow-up duration was 17.1 years (median).

Over the course of the study, 1324 deaths due to any cause were recorded; of these, cardiovascular causes accounted for 525 deaths. Assessment of TSH levels in the normal range and mortality revealed a U-shaped relationship between the two.

The risk of all-cause mortality was significantly increased among participants with high-normal TSH levels compared to those with medium-normal TSH levels with hazard ratio (HR) of 1.31. Cardiac-related mortality was also increased in this patient group with HR of 1.52. When the low-normal TSH level group was evaluated, the risk of all-cause and cardiac-related mortality was also found to be increased with HR of 1.39 and 1.69 respectively. This association was independent of other factors such as lifestyle factors, glycemic control, duration of diabetes, use of anti-diabetic medication, insulin resistance. In stratum-specific analyses, mortality risk was found to be higher among the younger patients (≤ 60 years) with diabetes but not in patients aged 60 years and older in the high-normal TSH group.

This prospective study, which followed patients for almost two decades, has shown a higher risk of all-cause and cardiovascular disease-related mortality in euthyroid adults with diabetes even if their TSH falls within the upper and lower limits of the reference range.

Reference

1. Zhu P, et al. TSH levels within the normal range and risk of cardiovascular and all-cause mortality among individuals with diabetes. Cardiovasc Diabetol. 2022 Nov 23;21(1):254. doi: 10.1186/s12933-022-01698-z.