We aimed to investigate the association of the status of iodized salt in terms of consumption of salt type and urinary iodine concentration (UIC) in diabetes, with frailty and examine whether this association could be modified by thyroid function.

A population-based cohort study.

We included 850 patients with type 2 diabetes from 11 communities in Shanghai, who completed five-year follow-up.

The type of salt consumed was collected through a standardized questionnaire and UIC was measured by an inductively coupled plasma-mass spectrometer. Frailty was assessed by frailty phenotype. Serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) were measured by electrochemiluminescence. Modified Poisson regression model with robust variance was used to estimate the relative risks (RRs) with 95% confidence intervals (CIs) for frailty in relation to iodized salt consumption and UIC.

In this five-year follow-up study in patients with diabetes, 111 (12.9%) patients progressed to frailty. Patients who consumed non-iodized salt (RR: 1.09, 95% CI: 1.01–1.18) had an increased risk of frailty, compared to patients who consumed iodized salt. Lower UIC was associated with a higher risk of frailty (1.10, 1.01–1.19). In patients with high TSH and low FT4, the RRs of frailty were 1.20 (1.08–1.34) and 1.15 (1.02–1.29) for non-iodized salt, and 1.14 (1.02–1.28) and 1.12 (0.99–1.27) for low UIC.

Non-iodized salt consumed and low UIC were associated with an increased risk of frailty in diabetes, particularly in those with high TSH and low FT4. Maintaining adequate iodine intake is critically important for preventing frailty in diabetes, especially for individuals with potential thyroid dysfunction.