Though free radicals have beneficial roles in the body to fight against certain pathogenic diseases as well as are implicated in a number of cellular and physiological activities, elevated levels may be overwhelming for the antioxidant defense system to maintain the normal homeostatic state. This may eventually lead to oxidative stress whereby the increased level of free radicals may attack certain biomolecules (DNA, RNA, proteins lipids and carbohydrates) causing damage to cells, tissues and organs in the body. Following these attacks, certain by-products formed which are indicative of the cellular damage have been identified and considered as biomarkers for assessing oxidative stress. As such, assays have been developed to quantify these oxidative stress markers in body tissues, biological fluids, blood, urine samples etc. Oxidative stress has been associated with several diseases such as diabetes, atherosclerosis, hypertension, respiratory diseases, arthritis, cataract, cancer, cardiovascular diseases etc., as free radicals are implicated in the pathogenesis of these diseases. The antioxidant defense system collectively made up of enzymes and some low molecular weight molecules are usually suppressed in a state of oxidative stress and thus, external sources of antioxidant have been required to supplement the endogenous antioxidants. As such, antioxidant supplementation has been of interest in managing oxidative stress diseases. However, the use of antioxidant supplements remain controversial as some studies have shown possible harmful effects. Thus, there is need for further randomised clinical trials with defined and specified dosage that will make use of suitable controls and biomarkers for various diseases to better predict the efficacy of antioxidant supplements across a broad spectrum of diseases in order to valourise their usage.