Association between Insulin Resistance and Metabolic Syndrome with Thyroid Status in Normal and Overweight/Obese Population: A Review

Abstract

Background: Hypothyroidism has multiple etiologies and manifestation where accurate diagnosis and appropriate treatment is required and is in?uenced by coexisting medical conditions. This paper describes evidence-based clinical causes and indications. Objective: The objective is to review the clinical effect of hypothyroidism in different selected aspects and summarize the potential evidence about relationship between subclinical hypothyroidism with cardiovascular disease, diabetes mellitus, insulin resistance and mortality. Data Sources: A systematic review was conducted by searching English-language articles identified from 23 databases and search engines, yielding over 1000 documents. Study Selection: They are reports on the effects of hypothyroidism versus euthyroidism on obesity, insulin resistance, cardiovascular disease, coronary heart disease and mortality. Data Extraction: Data from research articles on hypothyroidism including subclinical hypothyroidism (SCH) and overt hypothyroidism, insulin resistance including diabetes mellitus and risk for coronary heart disease (CHD) including metabolic syndrome were independently assessed and summarized. Data Synthesis: Twelve of twenty-nine identified studies involved population-based cohorts, case controls and retrospective studies that included 4306 subjects. All 13 studies examined risks associated with subclinical hypothyroidism with type 2 diabetes mellitus (T2DM) and prevalence rates of SCH in T2DM patients ranged from 4.69% to 64.28% in the 12 included studies. Moreover, 4 studies out of the above 12 studies have revealed insulin resistance in the participants. Another population-based 12 studies have been carried out to assess hypothyroidism-related cardiac manifestation and according to the given data, average prevalence of CHD in hypothyroid participants is 25.20 (vary from 3.73 to 47.14) and it is 13.90 in euthyroid participants (vary from 1.17 to 38.49). Conclusions: Type 2 diabetes mellitus people are more likely to get subclinical hypothyroidism and subclinical hypothyroid population also shows several complications associated with type 2 diabetes mellitus. Besides, subclinical thyroid dysfunction might represent a risk factor for coronary artery disease and mortality.