Thyrotropin and free thyroxine levels and coronary artery disease: cross-sectional analysis of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Plasma TSH and cardiovascular disease in the general population: A Mendelian randomization study of 105,224 individuals

BACKGROUND AND AIMS

The association between thyroid stimulating hormone (TSH) and cardiovascular disease has mainly been determined using clinical categories of disease. We tested the hypothesis that TSH on a continuous scale is associated with risk of atrial fibrillation (AF), myocardial infarction (MI), stroke, heart failure (HF), aortic valve stenosis (AVS), and major adverse cardiovascular events (MACE) and whether these associations are likely to be causal.

METHODS

We first tested whether plasma TSH on a continuous scale was observationally associated with incident cardiovascular events in a prospective cohort study of 105,224 individuals from the Copenhagen General Population Study followed for a median 7 years. Next, we tested whether a genetic risk score weighted on TSH was associated with cardiovascular endpoints. Finally, using Mendelian randomization, we tested whether the observed associations were likely to be causal.

RESULTS

Using restricted cubic splines, lower concentrations of TSH relative to the population median (=1.53 mIU/L) were associated with higher risk of AF, MI, stroke, HF, AVS, and MACE. Comparing individuals with TSH ≤5th percentile (≤0.54 mIU/L) versus >50th percentile (>1.53 mIU/L), hazard ratios (HRs) ranged from 1.12 (1.00-1.26) for stroke to 1.27 (1.11-1.46) for HF. Genetic risk estimates per standard deviation decrease in TSH were 1.28 (1.08-1.52) for AF, 1.35 (1.06-1.71) for MI, 1.06 (0.89-1.26) for stroke, 1.19 (0.94-1.52) for HF, 1.53 (1.03-2.26) for AVS, and 1.09 (0.97-1.23) for MACE.

CONCLUSIONS

In 105,224 individuals from the general population low plasma TSH was observationally and genetically associated with increased risk of AF, MI, and AVS suggesting that these observations may reflect causal pathways.

Clinical Parameters Are More Likely to Be Associated with Thyroid Hormone Levels than with Thyrotropin Levels: A Systematic Review and Meta-Analysis

Background: Though the functional states of other endocrine systems are not defined on the basis of levels of controlling hormones, the assessment of thyroid function is based on levels of the controlling hormone thyrotropin (TSH). We, therefore, addressed the question as to whether levels of thyroid hormones [free thyroxine (fT4), total triiodothyronine (TT3)/free triiodothyronine (fT3)], or TSH levels, within and beyond the reference ranges, provide the better guide to the range of clinical parameters associated with thyroid status. Methods: A PubMed/MEDLINE search of studies up to October 2019, examining associations of levels of thyroid hormones and TSH, taken simultaneously in the same individuals, with clinical parameters was performed. We analyzed atrial fibrillation, other cardiac parameters, osteoporosis and fracture, cancer, dementia, frailty, mortality, features of the metabolic syndrome, and pregnancy outcomes. Studies were assessed for quality by using a modified Newcastle-Ottawa score. Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were followed. A meta-analysis of the associations was performed to determine the relative likelihood of fT4, TT3/fT3, and TSH levels that are associated with the clinical parameters. Results: We identified 58 suitable articles and a total of 1880 associations. In general, clinical parameters were associated with thyroid hormone levels significantly more often than with TSH levels-the converse was not true for any of the clinical parameters. In the 1880 considered associations, fT4 levels were significantly associated with clinical parameters in 50% of analyses. The respective frequencies for TT3/fT3 and TSH levels were 53% and 23% (p < 0.0001 for both fT4 and TT3/fT3 vs. TSH). The fT4 and TT3/fT3 levels were comparably associated with clinical parameters (p = 0.71). More sophisticated statistical analyses, however, indicated that the associations with TT3/fT3 were not as robust as the associations with fT4. Conclusions: Thyroid hormones levels, and in particular fT4 levels, seem to have stronger associations with clinical parameters than do TSH levels. Associations of clinical parameters with TSH levels can be explained by the strong negative population correlation between thyroid hormones and TSH. Clinical and research components of thyroidology currently based on the measurement of the thyroid state by reference to TSH levels warrant reconsideration.

Subclinical Thyroid Dysfunction and the Risk of Cardiovascular Disease

The prevalence of subclinical hypothyroidism (SH) is 3-10%. The prevalence of subclinical hyperthyroidism (SHr) is 0.7-9.7%. Thyroid hormones affect cardiac electrophysiology, contractility, and vasculature. SH is associated with an increased risk of coronary heart disease (CHD), especially in subjects under 65. SHr seems to be associated with a slightly increased risk of CHD and an increase in CHD-related mortality. Both SH and SHr carry an increased risk of developing heart failure (HF), especially in those under 65. Both SH and SHr are associated with worse prognoses in patients with existing HF. SH is probably not associated with atrial fibrillation (AF). SHr, low normal thyroid-stimulating hormone (TSH) and high normal free thyroxine (FT4) are all associated with the increased risk of AF. An association between endothelial dysfunction and SH seems to exist. Data regarding the influence of SHr on the peripheral vascular system are conflicting. SH is a risk factor for stroke in subjects under 65. SHr does not increase the risk of stroke. Both SH and SHr have an unfavourable effect on cardiovascular disease (CVD) and all-cause mortality. There is a U-shaped curve of mortality in relation to TSH concentrations. A major factor that modifies the relation between subclinical thyroid disease (SCTD) and mortality is age. SH increases blood pressure (BP). SHr has no significant effect on BP. Lipids are increased in patients with SH. In SHr, high-density lipoprotein cholesterol and lipoprotein( a) are increased. SCTD should be treated when TSH is over 10 mU/l or under 0.1 mU/l. Treatment indications are less clear when TSH is between normal limits and 0.1 or 10 mU/L. The current state of knowledge supports the understanding of SCTD's role as a risk factor for CVD development. Age is a significant confounding factor, probably due to age-associated changes in the TSH reference levels.

[State of the coronary arteries and assessment of the role of hormone replacement therapy in patients with coronary heart disease against the background of primary manifest hypothyroidism]

Aim To study features of coronary damage and incidence of different types of acute coronary syndrome (ACS) in history associated with primary symptomatic hypothyroidism in patients with ischemic heart disease (IHD) and possible associations of replacement hormonal therapy with lipidogram indexes.Material and methods This retrospective study included 344 patients with IHD and functional class I-III stable angina (ССS, 1976). Of them 100 patients had primary symptomatic hypothyroidism and 244 had no hypothyroidism. Coronary angiography was performed for all patients included into this study. Routine laboratory, instrumental and clinical indexes were analyzed. Hypothyroidism was confirmed by levels of thyrotropic hormone, free triiodothyronine, and thyroxine. Comparative analysis was performed for the incidence of ACS types in history, types of coronary injury, and laboratory, instrumental and clinical indexes with assessment of potential interrelations. Statistically significant results were reported. Type of data distribution was evaluated with the Kolmogorov-Smirnov test. Quantitative data with normal (Gaussian) distribution were presented as mean (M) and standard deviation (SD). Data with attributes of non-normal distribution were presented as median (Me) with maximum and minimum values (min; max). Statistical significance of differences between means was assessed with the Mann-Whitney test. Logistic regression analysis was used in parallel for evaluating dependence of a quantitative variable on values of two or more quantitative or qualitative variables (factors). Significance level for testing of statistical hypotheses was р&lt;0.05.Results Incidence of ST segment elevation ACS (STEACS) was significantly higher in IHD patients with hypothyroidism than in the group without hypothyroidism (61.6 and 35.6 %, р=0.03) and also with three-vessel coronary artery disease (60.6 and 30.6 %, р=0.001). In the IHD group with hypothyroidism, levels of total cholesterol, triglycerides, and low- and very low-density lipoproteins were significantly increased compared to the respective values in patients without hypothyroidism (р&lt;0.0001). An inverse correlation was found between lipidogram indexes and L-thyroxine (р&lt;0.0001).Conclusion The incidence of STEACS associated with primary symptomatic hypothyroidism in history was significantly higher in the patient group with IHD on the background of primary symptomatic hypothyroidism compared to the comparison group. Also, the incidence of three-vessel coronary disease was significantly greater than in the IHD patient group without hypothyroidism. A significant association was found between the replacement hormonal therapy and the best lipidogram indexes. The authors suggested that the key factor for prevention of adverse cardiovascular events in IHD with hypothyroidism is achieving control of clinical manifestations of hypothyroidism with replacement hormonal therapy.

Thyroid disorders in Brazil: the contribution of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Thyroid disorders are common diseases, both in Brazil and worldwide. The Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) is a prospective cohort study that investigates cardiovascular diseases, diabetes, and associated factors, including non-classical cardiovascular risk factors such as thyroid function. Thyroid function was classified according to thyrotropin stimulating hormone (TSH), free thyroxine (FT4), and use of medication to treat thyroid disorders, after excluding participants who reported use of any medication that could alter the results of the TSH and FT4 tests. All analyses included in this review are cross-sectional using baseline data (2008 to 2010). The results showed an association of subclinical thyroid disorders with biomarkers of subclinical atherosclerosis, measured by carotid intima-media thickness and coronary artery calcium, insulin resistance, metabolic syndrome, and some psychiatric disorders. No association was found with the biomarker of inflammation high-sensitivity C-reactive protein, or changes in pulse wave velocity or heart rate variability.