Beta-carotene status dependent on total antioxidants

By Stephen Daniells

- Last updated on GMT

The blood levels of beta-carotene are tied to the total level of
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

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