Vitamin E Research Today is a free monthly online journal that collates and summarizes the latest research about Vitamin E, including details on benefits, dosage, supplements, antioxidants.

Do dietary antioxidants alleviate the cost of immune activation? An experiment with greenfinches.

Hõrak P, Saks L, Zilmer M, Karu U, Zilmer K

Institute of Zoology and Hydrobiology, Tartu University, Vanemuise 46, 51014 Tartu, Estonia. horak@ut.ee

Reactive oxygen and nitrogen species produced by metabolism and immune defenses can cause extensive damage to biomolecules. To counteract this damage, organisms rely on exogenous and endogenous antioxidants, although their relative importance in maintaining redox balance is unclear. We supplemented captive greenfinches with dietary antioxidants--carotenoids and vitamin E--and injected them with an inflammatory agent, phytohemagglutinin. Compared to controls, immune-challenged birds circulated more lipid peroxidation products but also increased total plasma antioxidativity. Carotenoid (but not vitamin E) supplementation generally reduced lipid peroxidation, but this did not compensate for the effects of immune activation. Levels of an endogenous antioxidant--uric acid--strongly contributed to plasma antioxidativity. We found no evidence that dietary antioxidants are immunostimulatory. These results demonstrate the antioxidant function of carotenoids in birds and show that simultaneous assessment of oxidative stress-driven damage, antioxidant barrier, and individual antioxidants is critical for explaining the potential costs of immune system activation.

Published 24 September 2007 in Am Nat, 170(4): 625-35.
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