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RespirAid - Affect on plasma vitamin C and vitamin E

QUESTION: Does Feeding an Oral Antioxidant Supplement Increase Plasma Vitamin C & E Concentrations in Adult and Aged Horses?


  • Vitamins C and E are important antioxidants in lung fluid and lung tissue1. Inflammation, caused by allergy (e.g. equine asthma) or infection (e.g. virus or bacteria) causes reduction in antioxidants which allows inflammation to persist2,3.
  • Supplementation with oral antioxidants has previously been shown to reduce airway inflammation and associated clinical signs in horses4,5.

Aim of Study

To determine the ability of an oral antioxidant supplement (RespirAid, Science Supplements) to raise plasma vitamin C and E concentrations in horses. As older horses may experience higher levels of oxidative stress and have a higher requirement for antioxidant vitamins, both adult and aged groups of horses were studied.

Study Design

  • Placebo-controlled = some horses received the active supplement and some received a supplement with no active ingredients (placebo). Use of a placebo helps reduce bias (seeing a false positive result) and allows for the fact that an improvement might be observed from horses spontaneously improving.
  • Randomised = which horses were given placebo was pre-determined by a random system rather than a person deciding at the time of seeing a horse. This removes bias in the results caused by selecting only certain horses to have a particular treatment.
  • Blind = researchers did not know which horses received the active supplement and or placebo supplement. Blinding removes bias caused by people wanting to see a positive effect with the active supplement.

Study Outline

Twenty aged (minimum of 20 years old) horses and 20 adult (5-12 years old) horses were studied. Ten aged and 10 adult horses were fed RespirAid at the recommended rate for 6 weeks. The remaining 10 aged and 10 adult horses were fed a placebo for 6 weeks. Blood samples for analysis of plasma Vitamin C and E concentration were collected every 2 weeks.


  • Plasma Vitamin C (Figure 1a) and Vitamin E (Figure 1b) concentrations were significantly increased after 2 weeks in both the aged and adult groups of horses fed the antioxidant supplement RespirAid, but were unchanged in the placebo fed group.
  • In the horses given the antioxidant supplement, there was no significant difference in plasma Vitamin C & E concentrations between aged and adult horses after supplementation, indicating that aged horses are comparable with adult horses in their ability to absorb antioxidants from the diet.
    Changes in plasma Vitamin C and Vitamin E under RespirAid

    Figure 1: Mean (+ standard deviation) plasma Vitamin C (a) and Vitamin E (b) concentrations in adult and aged horses before (Pre) and after supplementation (S) for 6 weeks (w) with either an antioxidant rich supplement (RespirAid) or placebo. Each group consists of 10 young horses and 10 aged horses. * = Significantly different compared to Pre (P < 0.0001).

    Take Home Message

    • An oral antioxidant and key trace mineral supplement (RespirAid) is able to increase and maintain plasma Vitamin C and Vitamin E concentrations when fed to both adult and aged horses.


    1. Deaton, C.M. et al. (2003) Pulmonary bioavailability of ascorbic acid in an ascorbate-synthesising species, the horse. Free Radic Res 37, 461-467
    2. Deaton, C.M. et al. (2004) Pulmonary epithelial lining fluid and plasma ascorbic acid concentrations in horses affected by recurrent airway obstruction. Am J Vet Res 65, 80-87.
    3. Deaton, C.M. et al. (2005) Effect of acute airway inflammation on the pulmonary antioxidant status. Exp Lung Res 31, 653-670.
    4. Deaton, C.M. et al. (2002) Antioxidant supplementation and pulmonary function at rest and exercise. Equine Vet J Suppl, 58-65.
    5. Deaton, C.M. et al. (2004) Antioxidant supplementation in horses affected by recurrent airway obstruction. J Nutr 134, 2065S-2067S.
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