Kidney diseases and the thyroid: interactions and consequences

Deep concern has been raised about the reduced survival rate in patients with renal impairment, and efforts to identify comorbidities that could delay its progression are of paramount importance. Among them, thyroid dysfunction has been postulated as one of the determinants of chronic kidney disease (CKD). It is worth noting that the relationship between the thyroid gland and the kidney is mutual. Although patients with CKD can exhibit changes in thyroid function tests that characterize non-thyroidal illness syndrome, thyroid hormones per se are critical regulators of kidney structure and function. A growing number of studies indicate that subclinical hypothyroidism is more common in people with CKD than in the general population and could be considered a risk factor for the development of CKD. However, it remains unclear whether hypothyroidism has a causal role in the development of CKD or whether levothyroxine treatment could minimize the progressive loss of kidney function in these patients. Overall, this narrative Review intends to explore the potential involvement of thyroid dysfunction, with a focus on hypothyroidism, as a reversible risk condition in the deterioration of renal function.