Association between dietary salt intake and early renal impairment in elderly patients with type 2 diabetes: a cross-sectional study in central and southern China

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Objective This study aims to investigate the association between dietary salt intake and early renal impairment in elderly patients with type 2 diabetes.Design A retrospective cross-sectional study.Setting A health management centre of a large tertiary hospital in Hunan province, China, which is also one of the largest health management centres in central and southern China.Participants A total of 1027 elderly patients with type 2 diabetes participated in the study from 2017 to 2024.Primary and secondary outcome measures All participants completed a self-administered health assessment questionnaire before undergoing routine check-ups. Daily salt intake was calculated based on the 24-hour urinary sodium excretion. Early renal impairment was defined as urinary albumin to creatinine ratio (UACR) between 30 and 300 mg/g. Multivariable binary logistic regression and restricted cubic spline analyses assessed the association between dietary salt intake and early renal function impairment.Results Early renal impairment prevalence was 44.69%. Among 1027 participants, 678 (66.0%) were classified as G1 (estimated glomerular filtration rate (eGFR) ≥90 mL/min/1.73 m²) and 349 (34.0%) as G2 (eGFR 60–89 mL/min/1.73 m²). Age ≥75 years, higher dietary salt intake, systolic blood pressure, fasting blood glucose, preference for smoked and pickled foods and alcohol consumption were independently associated with early renal function impairment in elderly type 2 diabetes. After adjustment for potential confounders, participants with the highest salt intake (≥9.46 g/day) had a significantly higher risk of UACR positivity than those with the lowest intake (≤6.63 g/day) (OR=1.619, 95% CI 1.098 to 2.387, p=0.015). Each quartile increase in salt intake was associated with an approximately 11% increase in UACR (B=0.104, 95% CI 0.041 to 0.167, p=0.001). In analyses stratified by chronic kidney disease stage, the association was significant in the G1 subgroup (p=0.002) but not in the G2 subgroup (p=0.783). Using the median salt intake (8.10 g/day) as reference, a linear positive association was observed between dietary salt intake and UACR positivity.Conclusions In this cross-sectional study, high salt intake was independently associated with early renal impairment in elderly patients with type 2 diabetes after adjustment for available confounders. Higher salt intake corresponded to progressively higher UACR positivity, and no obvious threshold was observed in the restricted cubic spline analysis. However, the cross-sectional design precludes causal inference, and longitudinal studies are needed to confirm these findings.