The sodium-blood pressure variability paradox and sub-clinical atherosclerosis in normotensive Chinese adults: a cross-sectional study

Background and purpose: Sodium intake influences blood pressure (BP) regulation and BP variability (BPV), both of which are linked to vascular health. However, how sodium intake and BPV relate to sub-clinical atherosclerosis in normotensive populations remains unclear. This study aimed to examine the associations among sodium intake, BPV, and sub-clinical atherosclerosis in healthy Chinese adults. Methods: In this cross-sectional study, 264 middle-aged, normotensive Chinese adults (mean age 54.2 ± 6.5 years; 55.3% men) underwent office and 24-hour ambulatory BP monitoring to derive systolic and diastolic BPV indices (standard deviation and coefficient of variation). Urinary sodium excretion was estimated from a single morning spot urine sample using the Kawasaki formula. Carotid intima-media thickness (CIMT) was measured by ultrasonography and used as a marker of sub-clinical atherosclerosis. Participants were stratified by the 75th percentile of CIMT to define increased CIMT. Logistic and linear regression analyses evaluated relationships between urinary sodium, BPV parameters, and CIMT. Additional subgroup analyses were performed stratified by sex, age (<55 vs. ≥55 years), and daytime systolic BP (median split). A sensitivity analysis using the conventional CIMT cutoff of 0.9 mm was also conducted. Results: Higher nighttime systolic BP and BPV were positively correlated with CIMT, whereas lower urinary sodium excretion was inversely associated with daytime BPV. Daytime BPV showed a paradoxical inverse association with increased CIMT in the overall analysis. In subgroup analyses, these associations were consistent across sex, age, and daytime BP categories, with no significant effect modification (all P > 0.20). No participants reached CIMT ≥ 0.9 mm, precluding analysis at that threshold. Conclusions: In healthy, normotensive adults, lower sodium intake (estimated by urinary sodium) was associated with higher daytime BPV, while higher nighttime BP and BPV correlated with increased CIMT. The inverse relationship between daytime BPV and sub-clinical atherosclerosis was consistent across demographic and metabolic subgroups, suggesting that moderate BPV may reflect physiological vascular adaptability rather than damage in this low-risk cohort.