Thyroid-stimulating hormone levels in the normal range and incident type 2 diabetes mellitus

Abstract

AimTo evaluate the relationship between thyroid-stimulating hormone (TSH) levels within the normal range and the risk of type 2 diabetes mellitus (T2DM) in a cohort of patients at high cardiovascular risk, and to perform a systematic review and meta-analysis of previous studies.MethodsWe included 5542 patients without T2DM from the prospective Secondary Manifestations of ARTerial disease study with TSH levels between 0.35 and 5.0 mIU/L without anti-thyroid medication or thyroid-hormone replacement therapy. Cox regression was used to investigate the relationship between baseline plasma TSH levels and incident T2DM. MEDLINE, EMBASE, and Cochrane were searched for prospective cohorts assessing TSH and incident T2DM. Hazard ratios (HR) from included prospective cohort studies were pooled using a random-effects model.ResultsIn patients at high cardiovascular risk, higher plasma TSH levels in the normal range were not associated [HR 1.07 per mIU/L increase in TSH (95% confidence interval (95% CI) 0.95–1.22)] with an increased risk of T2DM, adjusted for age, sex, smoking, total and HDL cholesterol, and triglycerides. In the meta-analysis involving three prospective cohort studies, including the present study, including 29,791 participants with 1930 incident events, there was no relation between plasma TSH levels in the normal range and incident T2DM [pooled HR 1.06 (95% CI 0.99–1.14)].ConclusionThere is no apparent relation between plasma TSH levels in the normal range and incident T2DM in patients at high cardiovascular risk.Electronic supplementary materialThe online version of this article (10.1007/s00592-018-1231-y) contains supplementary material, which is available to authorized users.

<p>Thyroid Hormone Changes in Euthyroid Patients with Diabetes</p>

“…None of the previous studies excluded the impact of thyroid autoimmunity, which may slightly affect the results. 15 , 26 - 28 To be noted, two cohort studies from the Netherlands included Caucasian adults with higher cardiovascular risks than our study population, 15 , 28 while the Korean study was more in line with us. 26 , 27 It suggested this association could be ethnicity-based and needed more validation in different populations.…”

“… 26 , 27 However, a cohort study from Rotterdam suggested that higher TSH levels and lower FT4 levels within the reference range of thyroid function were associated with a higher risk of diabetes, 15 while another cohort study in the Netherlands showed no association between plasma TSH levels and incident T2DM. 28 Cross-sectional studies in Korea and Peru suggested increased FT3 and FT3/FT4 ratio are associated with metabolic syndrome and insulin resistance. 29 – 31 The difference in these results may be explained by the study population.…”

Variation in Normal Range Thyroid Function Affects Serum Cholesterol Levels, Blood Pressure, and Type 2 Diabetes Risk: A Mendelian Randomization Study

“…Recently, a large population-based prospective study in 8452 participants reported an increased risk of incident T2D in individuals with low-normal thyroid function (13). However, a following meta-analysis in nearly 30,000 participants did not confirm these findings (69).…”

The changes of thyroid hormone in euthyroid patients with diabetes

“…Interestingly, two longitudinal studies from Korea did not prove a statistically significant association between the incidence of diabetes and the suppressed TSH level, but the individual-level changes of TSH (25,26). However, a cohort study from Rotterdam suggested that higher TSH levels and lower FT4 levels within the reference range of thyroid function were associated with a higher risk of diabetes (15), while another cohort study in Netherland showed no association between plasma TSH levels and incident T2DM (27). The difference of these results can be explained by the study population.…”