Association between serum 25(OH)D and risk of all-cause mortality in adults with prior cardiovascular disease: a cohort study from NHANES 2007–2018

BACKGROUND: Serum vitamin D deficiency is common in the patients with cardiovascular disease (CVD), but the association between serum vitamin D levels and risk of all-cause mortality in patients with CVD is controversial. OBJECTIVE: This study aimed to understand better the association between serum 25(OH)D status and risk of all-cause mortality in patients with prior CVD. METHOD: We conducted a cohort study using data from the National Health and Nutrition Examination Survey from 2007 to 2018 to investigate the association between serum 25(OH)D and the risk of all-cause mortality using multivariate Cox regression models, with further subgroup analyses and interactions smooth curve fitting to address possible nonlinearities. RESULT: A total of 3220 participants with prior CVD were included in this study, with a total of 930 deaths over a median follow-up of 5.52 years, with multivariable-adjusted serum vitamin D levels after natural log transformation (4.31–4.5 ) as a reference in COX regression, and corrected HRs and 95% CIs of 1.81 (1.31, 2.50), 1.34 (1.07, 1.66), 1.28 (1.05, 1.56),1.00 (reference), 1.10 (0.89, 1.37) for all-cause mortality, respectively. Results remained robust in the stratified analysis of interactions, but a L-shaped relationship was detected. We identified an inflection point of 4.5 after multivariate adjustment through a two-stage linear regression model and recursive algorithm. CONCLUSION: Our findings demonstrate that increasing serum 25(OH)D levels may have a L-shaped relationship with risk of all-cause mortality and that increases in serum 25(OH)D levels do not continue to reduce the risk of all-cause mortality. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12872-023-03257-0.