The present study was carried out with the aim to analyze the role of creatine on oxidative stress during exercise, i.e. whether creatine is a pro-oxidative or an antioxidant substance.

In a randomized double-blind study involving 30 adult males, we examined plasma lactate, oxidative stress markers (malondialdehyde, MDA) and glutathione redox ratio (GSSG•GSH^-1), antioxidative systems (vitamins A, E, C), and ergospirometric responses (respiratory quotient and relative oxygen uptake) before and after 30 min steady-state tests 75% O_2max (placebo and creatine).

Ergospirometric tests, haematocrit values, blood lactate as well as vitamins A, E and C concentrations did not show significant differences between creatine and placebo testing. Conversely, oxidative stress markers MDA and GSSG•GSH^-1 increased during placebo trials much more than in creatine trials.

This is the first report documenting that a creatine loading, i.e. a 0.3 g/kg/die of creatine ingestion for 5 consecutive days, could reduce the oxidative stress, whereas its consumption may not have a clear metabolic advantage in certain aerobic activities.