Higher Carotid Intima-Media Thickness in Subclinical Hypothyroidism Associated with the Metabolic Syndrome

The Relationship between Subclinical Hypothyroidism and Carotid Intima-Media Thickness as a Potential Marker of Cardiovascular Risk: A Systematic Review and a Meta-Analysis

BACKGROUND AND OBJECTIVES

Thyroid dysfunction is known to have significant consequences on the cardiovascular system. The correlation between carotid intima-media thickness (CIMT) and subclinical hypothyroidism (SCH) has been frequently evaluated in clinical studies in recent years. This study aimed to evaluate the significance of this association through a meta-analysis.

METHODS

We conducted a systematic search of PubMed, MedLine, Scopus, and Web of Science databases using the keywords 'subclinical hypothyroidism and carotid intima-media thickness', from the beginning of each database until January 2023. We established the inclusion and exclusion criteria and considered studies that met the inclusion criteria. We used Jamovi for statistical analysis of the data.

RESULTS

We identified 39 observational studies that met the inclusion criteria, with 3430 subjects: 1545 SCH and 1885 EU. Compared to euthyroid subjects (EU), subjects with subclinical hypothyroidism (SCH) had significantly increased carotid intima-media thickness (CIMT) values; the estimated average mean difference was 0.08 (95% CI 0.05 to 0.10), p < 0.01, I2 = 93.82%. After the sensitivity analysis, a total of 19 from the 39 abovementioned studies were analyzed, with most studies showing a positive association between SCH and thickening of the carotid wall; the estimated average mean difference was 0.04 (95% CI 0.02 to 0.07), p = 0.03, I2 = 77.7. In addition, female sex, advanced age, and high cholesterol levels statistically significantly influenced this association.

CONCLUSIONS

Our meta-analysis indicates a significant positive association between SCH and increased CIMT, but with some limitations.

Subclinical Hypothyroidism and Metabolic Syndrome: A Common Association by Chance or a Cardiovascular Risk Driver?

The metabolic syndrome (MS) and subclinical hypothyroidism (SCH) are highly prevalent in the general population. Cross-sectional epidemiological data suggest that a mutual association exists between the two, although the cause-effect relationship remains poorly elucidated. As SCH raises cholesterol, blood pressure, and visceral fat, it is easy to understand why it associates with MS. Rather, the reasons whereby MS patients are at higher risk for SCH are less apparent. Some studies have reported that SCH is itself characterized by high cardiovascular risk. Therefore, the coexistence of SCH and MS may identify subjects at a particularly high risk for future cardiovascular events. Recent data published in Metabolic Syndrome and Related Disorders indicate that carotid intima-media thickness, a marker of initial atherosclerosis and a possible predictor of future events, is higher in patients with both SCH and MS than in the presence of each condition alone. In this Editorial, we discuss the clinical implications of SCH and MS association and the interpretation of such recent findings.