It has been suggested that dietary antioxidants reduce the level of oxidative DNA damage induced by reactive oxygen species. However, there are limited in vivo studies which support this hypothesis as a number of epidemiological studies showed no such effect following dietary supplementation with carotenoids, vitamin C, or E [1, 2]. Urinary concentration of 8-hydroxy-2′-deoxyguanosine (8-oxodG, a base damage formed by reactive oxygen species) has been used as a non-invasive biomarker of oxidative DNA base damage in a number of studies [3, 4].
Reactive oxygen species (ROS) have been suggested to play an important role in mutagenesis, carcinogenesis, and aging processes. ROS can react with different cellular components e.g., proteins, lipids and nucleic acids, and give rise to chemical modifications. Under normal conditions cellular antioxidant enzymes and other antioxidants in the cell detoxify elevated levels of ROS and minimize damage to intracellular components. However, under extensive physiological activity ATP consumption will increase followed by increased oxygen consumption and, as a consequence, the production of ROS will increase . Healthy and/or well-trained persons and vegetarians seem to have increased protection against ROS-induced damages . It suggests that regular physical exercise  and a diet rich in antioxidant  may have a protective effect towards ROS-induced damage, in particular DNA base damage. One of the frequently studied DNA base damages is 8-oxodG. Highly effective repair mechanisms are operating both on DNA (e.g., hOGG1) and the nucleotide pool (hMTH1) to remove 8-oxodG/8-oxodGTP from the cell [9, 10]. Previously, we have shown that extracellular 8-oxodG originates from the nucleotide pool and may serve as a sensitive marker of oxidative stress . We have developed an ELISA method that allows the determination of the very low concentrations of 8-oxodG present in human blood serum [11–13].
In the present study we aimed to investigate the protective effect of tomato juice intake towards ROS induced by 20 min of extensive physical exercise. A novel finding in the present intervention study was that the level of 8-oxodG in human blood serum was increased significantly after 20 min acute physical activity possibly caused by an increase of the intracellular ROS level. No increase was observed when individuals had been drinking 150 ml tomato juice per day during a period of 5 weeks suggesting that the intracellular nucleic acids and, in particular, the nucleotide pool were unaffected and well protected from the deleterious effect of ROS. The intervention study support the hypothesis that antioxidants (e.g. lycopene) supplied from tomato juice may protect against oxidative stress induced by extensive physical exercise.