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BackgroundThis study aimed to evaluate the relationship between magnesium (Mg) status, serum vitamin D (VD) concentration and mortality in congestive heart failure (CHF) patients.MethodsData for this study were extracted from the National Health and Nutrition Examination Surveys 2007–2018. Magnesium depletion score (MDS) is a scoring system developed to predict the status of Mg deficiency that considers the pathophysiological factors influencing the reabsorption capability of the kidneys. The primary outcome was all-cause mortality of CHF patients and the secondary outcome was mortality due to cardiovascular disease (CVD). Weighted univariate and multivariate cox proportional hazards models were used to explore the association between Mg status, serum VD concentration and all-cause mortality or mortality due to CVD in CHF patients, using hazard ratios (HRs) and 95 % confidence intervals (CIs). Subgroup analyses based on age, physical activity (PA), course of CHF, race, and body mass index were further assessed with regards to the association analysis.ResultsIn total, 1022 CHF patients were included, of whom 418 (40.90 %) died by 31st December 2019. After adjusting for all covariates, high MDS (>2 points) was related to a higher risk of all-cause mortality (HR = 1.72, 95 % CI: 1.30–2.29) and mortality due to CVD (HR = 1.71, 95 % CI: 1.29–2.25); a higher serum VD concentration was related to a lower risk of all-cause mortality (HR = 0.78, 95 %CI: 0.62–0.99) and mortality due to CVD (HR = 0.80, 95 % CI: 0.63–0.99). Compared to patients with high serum VD concentration and low MDS, patients with low serum VD concentration and high MDS had a high risk of all-cause mortality (HR = 2.44, 95 % CI: 1.54–3.85, p for trend = 0.043) and mortality due to CVD (HR = 2.41, 95 % CI: 1.32–4.40).ConclusionSerum VD and Mg status may have a combined effect in improving the prognosis in CHF patients, thus an appropriate level of serum VD and Mg intake may be beneficial to maintain cardiovascular health, thereby improving outcome.