Beta-carotene status dependent on total antioxidants
antioxidants, not solely to the carotenoid itself, says a new study
that may help explain discrepancies in the science about the
nutrient.
"Dietary total antioxidant capacity (TAC) is an independent predictor of plasma beta-carotene," wrote the authors from the University of Parma. "This may explain, at least in part, the inverse relationship observed between plasma beta-carotene and risk of chronic diseases associated to high levels of oxidative stress (ie. diabetes and CVD), as well as the failure of beta-carotene supplements alone in reducing such risk."
While epidemiological studies have generally supported the health benefits of beta-carotene, particularly as a protective factor against type-2 diabetes, and cardiovascular events, many intervention studies that have provided the carotenoid as an isolated supplement have failed to demonstrate a significant decrease in risks.
However, such discrepancies does not mean the carotenoid does not confer any benefits.
Writing in the European Journal of Clinical Nutrition, the researchers report the findings from their cross-sectional study of 247 healthy people (140 men). Dietary intakes were evaluated using three-day food records.
They report that increasing blood levels of the carotenoid were indeed associated with decreasing risk factors for diabetes and CVD, including C-reactive protein, triglyceride levels, and gamma-glutamyltranspeptidase (GGT).
Increasing intake of fat, fibre, fruits, vegetables, beta-carotene, vitamins C and E and dietary TAC were also associated with increasing plasma beta-carotene levels.
"Beta-carotene intake in the present study shows only a marginally significant relationship with plasma beta-carotene, which appears to be intimately associated with many dietary factors," wrote the researchers.
The results support the hypotheses that other antioxidants 'spare' the circulating beta-carotene, or that antioxidants worked together synergistically.
"As antioxidants with different activities and redox potentials synergistically network against oxidative stress and its consequences, including subclinical inflammation, the TAC-mediated effect of the usual diet on plasma beta-carotene could explain, at least in part, why this carotenoid is associated with low risk of chronic disease, but supplementation with beta-carotene fails to reduce such risk."
The results could also add to the ongoing debate as to the best way to test nutrients in a clinical trial setting. Currently, nutrients such as beta-carotene are tested by a drug-based (or evidence-based) approach, which focus on one single nutrient. Some scientists argue that such an approach pulls the nutrient 'out of context'.
Many clinical trials have also focused on the effect of a certain supplement in diseased or high-risk populations, which severely limits the ability of scientists to extend the findings to the wider, healthier population.
Source: European Journal of Clinical Nutrition Volume 61, Pages 69-76 "The total antioxidant capacity of the diet is an independent predictor of plasma beta-carotene" Authors: S Valtuena, D Del Rio, N Pellegrini, D Ardigo, L Franzini, S Salvatore, P M Piatt, P Riso, I Zavaroni and F Brighenti
