The total antioxidant capacity of the diet is an independent predictor of plasma beta-carotene concentrations

Objective: To investigate the contribution of the total antioxidant capacity (TAC) of the diet to plasma concentrations of β-carotene. Design: Cross-sectional study. Setting: Department of Public Health and Department of Internal Medicine and Biomedical Sciences, University of Parma. Subjects: A total of 247 apparently healthy adult men (n = 140) and women (n = 1 07). Methods: A medical history, a physical exam including height, weight, waist circumference and blood pressure measurements, a fasting blood draw, an oral glucose tolerance test and a 3-day food record. Results: We observe a negative trend across quartiles of plasma β-carotene for most biological variables clustering in the insulin resistance syndrome, as well as for traditional and new risk factors for type II diabetes and cardiovascular disease (CVD), including C-reactive protein and γ-glutamyltranspeptidase (P < 0.05). Regarding dietary characteristics, energy-adjusted intake of fat, fiber, fruits, vegetables, β-carotene, vitamin C, vitamin E and dietary TAC significantly increased with increasing plasma β-carotene (P < 0.05), whereas alcohol intake decreased (P = 0.013). Adjusted geometric means (95% confidence interval) of plasma β-carotene significantly increased across quartiles of dietary TAC, even when single dietary antioxidants were considered in the model (QI = 0.087mg/dl (0.073-0.102); QII = 0.087mg/dl (0.075-0.103); QIII = 0.114mg/dl (0.098-0.132) and QIV = 0.110mg/dl (0.093-0.130); P for linear trend = 0.026). When the population was divided on the basis of alcohol consumption, this trend was also observed in subjects drinking <20 g alcohol/day (P = 0.034), but not in those with higher alcohol intake (P = 0.448). Conclusions: Dietary TAC is an independent predictor of plasma β-carotene, especially in moderate alcohol drinkers. This may explain, at least in part, the inverse relationship observed between plasma β-carotene and risk of chronic diseases associated to high levels of oxidative stress (i.e., diabetes and CVD), as well as the failure of β-carotene supplements alone in reducing such risk.