Elevated levels of oxidative nucleic acid modifications have been proposed to be associated with some of the clinical characteristics of Down syndrome. Oral intake of coenzyme Q10 improves oxidative status and shows a tendency toward protective effect on DNA oxidation in certain age groups of children with Down syndrome. Here, we demonstrate that long-term (i.e., 4 years) treatment with coenzyme Q10 (ubiquinone) at the dosage of 4 mg/kg/d does not affect whole body DNA and RNA oxidation.