Effect of six weeks of oral echinacea purpurea supplementation on nitric oxide production

Background

Echinacea purpurea, a purple coneflower plant of the compositae family (Asteraceae), is native to North America and commonly used as an herbal supplement to enhance immune function. Echinacea purpurea has been shown to stimulate macrophage activity which is a known stimulator of nitric oxide (NO) production. Echinacea purpurea supplementation (8,000 mg·d^-1) in untrained (42.5 ± 1.6 mL·kg^-1·min^-1) males was shown to elicit a 63% increase (p < 0.05) in serum erythropoietin (EPO) following two weeks of supplementation. This is supported in part by earlier findings which indicated that four weeks of Echinacea purpurea supplementation demonstrated a non-significant increase in maximal oxygen uptake (VO_2max). It is plausible that Echinacea-induced EPO production may stimulate physiological responses independent of and/or in addition to erythropoiesis. There is also evidence suggesting EPO has vasculo-protective effects including the activation of endothelial nitric oxide synthase (eNOS). Based on these findings, a proposed non-hematological response to the Echinacea-induced increase in EPO could be enhanced NO production. The purpose of this investigation was to determine whether six weeks of oral Echinacea purpurea supplementation augmented NO production as a result of an Echinacea-induced increase in EPO and/or Echinacea-induced macrophage activity.

Methods

Twenty-four males (mean ± SE): age = 25.2 ± 1.4 yr, height = 178.1 ± 1.4 cm, mass = 78.1 ± 1.6 kg, percent body fat = 12.7 ± 0.9 %, VO_2max = 52.9 ± 0.9 mL·kg^-1·min^-1 were randomly grouped using a matched-pair, double-blind design and self-administered 8,000 mg·d^-1 (2,000 mg × 4 times·d^-1) of either Echinacea purpurea (ECH) (n=12) or placebo (PLA) (n=12) for 42 consecutive days. Blood samples were collected prior to supplementation (day-0) and every two weeks during the supplementation period (day-14, -28, and -42) and were analyzed for nitrite and total nitrite (nitrite/nitrate) concentrations. Separate 2 × 4 (Group × Time) factorial ANOVA with repeated measures on time were used to determine statistical differences with significance set at p ≤ 0.05.

Results

There were no significant interaction, group, or time effects observed following six weeks of supplementation for nitrite (µmol·L^-1) (ECH Pre: 0.88 ± 0.07 vs. ECH Post-42: 0.73 ± 0.10; PLA Pre: 0.91 ± 0.16 vs. PLA Post-42: 0.96 ± 0.22), nitrate (µmol·L^-1) (ECH Pre: 17.44 ± 1.85 vs. ECH Post-42: 20.16 ± 2.23; PLA Pre: 16.01 ± 1.50 vs. PLA Post-42: 14.77 ± 1.21), or nitrite/nitrate (µmol·L^-1) (ECH Pre: 18.32 ± 1.86 vs. ECH Post-42: 20.89 ± 2.25; PLA Pre: 16.92 ± 1.49 vs. PLA Post-42: 15.73 ± 1.22) or for any of the intermediate (day-14, -28) measurement points.

Conclusions

These results suggest that six weeks of oral Echinacea purpurea supplementation (8,000 mg·d^-1) did not significantly change nitrite, nitrate, or nitrite/nitrate. Therefore, Echinacea purpurea may not be an effective herbal supplement for enhancing NO production in apparently healthy, recreationally active, males with above average aerobic fitness (VO_2max = 52.9 ± 0.9 mL·kg^-1·min^-1).