Association of serum vitamin C and E levels with mortality in individuals with metabolic syndrome

Existing evidence suggests the importance of oxidative stress in the etiology of metabolic syndrome (MetS), which is a growing global health problem. However, the impact of serum antioxidant vitamins (C and E) levels on the clinical outcomes of the MetS population is unknown. This cohort study included 2102 adults diagnosed with MetS, who participated in the National Health and Nutrition Examination Survey from 2003 to 2006. Serum levels of vitamin C, α-tocopherol, and γ-tocopherol were measured. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were calculated using Cox proportional hazards models to analyze the association between serum levels of vitamins and the risk of mortality from all causes, CVD, and cancer. Analyses controlled for demographic characteristics, body mass index, smoking, drinking, diabetes, hypertension, and dyslipidemia. Among the 2102 participants, 731all-cause deaths were documented, including 270 CVD deaths and 52 cancer deaths. Compared to the reference group with serum vitamin C levels of 0.02–0.65 mg/dL, the multivariable-adjusted HRs for high vitamin C levels (1.08–4.26 mg/dL) were 0.65 (95% CI, 0.53–0.79) for all-cause mortality and 0.60 (95% CI, 0.42–0.85) for CVD mortality. Compared to the reference group with serum α-tocopherol levels of 354–1139 µg/dL, the adjusted HRs were 0.52 (95% CI, 0.33–0.83) for mid-range α-tocopherol levels (1140–1590 µg/dL) and 0.76 (95% CI, 0.46–1.25) for high-range levels (1591–6405 µg/dL) for cancer mortality. For serum γ-tocopherol, compared to the reference group (16–190 µg/dL), the HR for mid-range levels (191–315 µg/dL) was 1.79 (95% CI, 1.25–2.55) and for high-range levels (316–3122 µg/dL) was 1.74 (95% CI, 1.10–2.75) for CVD mortality. Our study highlights the clinical value of antioxidant vitamins in predicting the survival of the MetS population. Vitamin C are associated with a reduced risk of death from all causes and CVD in individuals with MetS. Mid-range α-tocopherol levels may decrease the risk of cancer mortality, while high-range γ-tocopherol levels could increase the risk of CVD mortality. Individuals with MetS may require more careful antioxidant vitamins supplement to prevent the development of other diseases and thereby reduce mortality.