BACKGROUND
Both thyroid disease and chronic kidney disease (CKD) are common conditions with significant clinical effects. Previous studies have identified a relationship between these 2 diseases. Hypothyroidism can damage the structure of the kidney, reducing its weight and mass and altering the kidney structure in animal studies. Furthermore, the reduction in the glomerular filtration rate (GFR), the most common measure of overall kidney function, has been observed in patients with hypothyroidism. The consequences of hyperthyroidism with regard to renal function are largely unknown. Some studies in patients with thyroid disease have also shown a link with CKD, although it is not yet clear if the thyroid is responsible for kidney failure.

In this study, the authors investigate whether hypothyroidism and hyperthyroidism are associated with higher CKD occurrence and progression.

THE FULL ARTICLE TITLE
You AS et al. Impact of thyroid status on incident kidney dysfunction and chronic kidney disease progression in a nationally representative cohort. Mayo Clin Proc 2024:39-56; doi: 10.1016/j.mayocp.2023.08.028. PMID: 38176833.

SUMMARY OF THE STUDY
This is a study of 4,152,830 adults; 59% were women, the average age was 55 years, and 75%were non-Hispanic White. Two TSH assessments determined thyroid status and to categorize the population into hypothyroid, euthyroid (normal thyroid function) and hyperthyroid groups, which were further subdivided according to the severity of thyroid disease. The TSH values were also assessed as a continuous predictor of development of CKD or CKD progression.

Hypothyroidism and hyperthyroidism were each present in 2.1% of the entire group, and the presence and progression of CKD were higher in both of these groups as compared to the euthyroid group. When subdivided according to severity, TSH levels in the high-normal/ hypothyroid range (≥3.0 mIU/L) and hyperthyroid range (<0.5 mIU/L) also were associated with a more significant risk of the presence of CKD or CKD progression.

In subgroup analysis, stronger associations between hypothyroidism CKD were observed for age <55 years, male sex, non-Hispanic Black race/ethnicity or absence of high blood pressure. In contrast, for hyperthyroidism, stronger estimates were found for subgroups of younger age, male sex, non-Hispanic White and Hispanic or absence of diabetes, coronary artery disease, congestive heart failure, atrial fibrillation, hyperlipidemia, or hypertension.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that both hypothyroidism and hyperthyroidism, in particular, TSH levels ≥3.0 mIU/L and <0.5 mIU/L, are risk factors for the development and progression of CKD. These findings show that abnormal levels of thyroid hormones have a negative impact on kidney function. Further studies to determine the effect of improvement in thyroid function on kidney function in patients with hypothyroidism or hyperthyroidism need to be done.

— Alan P. Farwell, MD

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