Relation of serum vitamin A levels to all-cause and cause-specific mortality among older adults in the NHANES III population

Although studies have suggested that vitamin A is associated with cardiovascular events and mortality, it remains unclear whether low doses or high doses of vitamin A have harmful effects on the cardiovascular system. This study investigated whether serum vitamin A levels are associated with all-cause and cause-specific mortality in US older adults.We analyzed the mortality information for 6069 participants aged 50 years or older who had serum vitamin A data available from the baseline examination. The participants were categorized as having deficient (<30 μg/dL), normal (30-80 μg/dL), or excessive (>80 μg/dL) levels of serum vitamin A, and a multivariate Cox proportional hazards regression analysis was performed on mortality. We found a U-shaped association between serum vitamin A levels and death from all-cause and cause-specific mortality among US adults. Comparing the normal range of serum vitamin A, the hazard ratio with deficient serum vitamin A was 2.9 (95% CI 2.0-4.3) for all-cause mortality, 2.1 (95% CI 1.1-4.1) for cardiovascular-related mortality and 2.5 (95% CI 1.2-5.3) for coronary artery disease-related mortality. Excessive serum vitamin A was associated with a 1.2-fold (95% CI 1.1-1.4) increased risk of all-cause mortality, a 1.4-fold (95% CI 1.2-1.8) increased risk of cardiovascular-related mortality, and a 1.5-fold (95% CI 1.2-2.0) increased risk of coronary artery disease-related mortality compared with the reference group.The finding suggests that serum vitamin A levels less than 30 μg/dL or greater than 80 μg/dL levels may indicate a high risk of subsequent mortality.