Radical oxygen species formed in human tissue cells by many endogenous and exogenous pathways, cause extensive oxidative damage, which has been linked to various human diseases. This review paper provides an overview of lipid peroxidation and focuses on the free-radicals initiated processes of LDL oxidative modification and DNA oxidative damage, which are widely associated to the initiation and development of atherosclerosis and carcinogenesis, respectively. The article subsequently provides an overview of the recent human trials or even in vitro investigations on the potential of natural antioxidant compounds (such as carotenoids, vitamins C and E) to monitor LDL and DNA oxidative changes.