**Abstract**

*Antioxidants*

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**184**

Humans possess defense mechanisms against free radicals: enzymatic and nonenzymatic antioxidants. Antioxidant defense is deficient in newborns and can be enhanced by the action of reactive oxygen species, generated by perinatal diseases such as respiratory distress or asphyxia. Prematurity itself will be associated with deficient antioxidant mechanisms, which are primarily enzymatic, but also nonenzymatic. Under oxidative stress conditions, antioxidant defense is overcome and thus, low-molecular weight free iron is released, which is not bound to transferrin and will play a role in Fenton's reaction, catalyzing lipid peroxidation. The generated ROS will in turn influence antioxidant defense mechanisms, stimulating their synthesis, as an adaptation mechanism of the body in response to the presence of increased ROS levels.

**Keywords:** antioxidants, newborn, oxidative stress
