Vitamin D deficiency, multimorbidity, and mortality in stage 2 cardiovascular-kidney-metabolic (CKM) Syndrome: evidence from the NHANES 2001–2018 cohort

This study aimed to compare mortality risks among patients with stage 2 cardiovascular-kidney-metabolic syndrome (CKM) across different multimorbidity states. Furthermore, it investigated whether sufficient serum vitamin D (≥75 nmol/L) modulates the association between multimorbidity and mortality. Using data from the 2001-2018 National Health and Nutrition Examination Survey (NHANES), we conducted a retrospective cohort study of 12,406 eligible patients. Among these patients, 913 died from all causes, and 223 died due to CVD. Survey-weighted Cox proportional hazards regression analyses revealed that compared to group 1 multimorbidity, groups 2 (all-cause mortality HR = 1.79; CVD mortality HR = 2.10), 3 (all-cause HR = 1.89; CVD HR = 1.76), and 4 (all-cause HR = 2.55; CVD HR = 3.97) had significantly increased mortality risks. Notably, sufficient serum 25-hydroxyvitamin D [25(OH)D] levels demonstrated a potential antagonistic effect on multimorbidity-related mortality, particularly for CVD. These findings indicate that maintaining adequate VD in stage 2 CKM patients may mitigate mortality risks associated with multimorbidity progression, offering insights for improving cardiovascular outcomes.