Cardiovascular Risk and Mild Thyroid Hormone Deficiency: Are there some Differences in the Elderly?

Abstract

EditorialSubclinical hypothyroidism (sHT) is a clinical condition defined as serum TSH concentration above the upper limit of the reference range in the face of normal free T4 (FT4) and free T3 (FT3) levels. Subclinical hypothyroidism, the prevalence of which increases with age, especially among women, up to almost 20%, encompasses several pathological entities, mainly represented by chronic autoimmune thyroiditis [1,2]. sHT is often associated to symptoms that resembles those of overt hypothyroidism, although to a lesser extent thus, the expression 'mild thyroid impairment' or 'mild thyroid hormone deficiency' would be more appropriate for defining such a condition [1]. Nonetheless, the term sHT is recognized worldwide and will be utilized in the present editorial. Since 90s, a relationship between sHT and increased cardio-vascular (CV) risk (both heart failure and coronary heart disease events) has been reported, although some experiences suggest that the risk may depend on the degree of TSH elevation [1,[3][4][5]. Moreover, several reports from elderly population (>65 years old) showed that this relationship seems no longer evident in such individuals especially in the oldest old (>85 years old) [6][7][8][9].The relationship between thyroid function and ageing has been hypothesized more than almost two decades ago [8]. Several clinical studies confirmed an age-dependent decrease of thyroid function including iodine uptake and thyroid hormone production [9]. However, it should be underlined that direct age-related changes need to be distinguished from the actual alterations induced by thyroid diseases or non-thyroidal illness. In this setting, conflicting results still exist regarding the serum TSH reference range and its modification with ageing between earlier reports (mainly case-control or crosssectional) and recent large naturalistic studies [3,[7][8][10][11][12][13][14]. Given that sHT is essentially recognized as abnormal serum TSH elevation, the definition of a worldwide recognized age-related reference range is clearly warranted.Thyroid hormones (TH) are implicated in maintaining and integrating metabolic homeostasis at multiple levels, and their deficiency can affect CV system by complex mechanisms involving both myocardium and vasculature, favouring hypertension and diastolic heart alteration. Moreover, sHT is associate to atherogenic conditions such as metabolic alterations, characterized by hypercholesterolemia and glucose intolerance as well as impaired coagulation [9]. These findings may explain the reported association between thyroid hormone deficiency and increased risk of CV diseases. However, whereas TH deficiency may contribute to atherogenic CV alterations (e.g. increase coronary heart disease (CHD) risk) in young adults (<65 years old) and moderate old patients (<75 years old), data from both humans and animal models showed a negative correlation between serum TH value and longevity [1,10]. In this setting, conflicting data are still existing on the association between sHT and CHD: some ...