Oxidative Stress and the Effects of Dietary Supplements on Glycemic Control in Type 2 Diabetes
Oxidative stress can be defined as a situation of imbalance in which the levels of pro-oxidants, referred to as reactive oxygen species (ROS) present in tissues, by far outweigh the amounts of neutralizing substances, otherwise known as antioxidants, as previously discussed . There is overwhelming evidence in the literature to show that this phenomenon is associated with both type 1 and type 2 diabetes [1–7]. Many experimental approaches have been used to demonstrate the association of oxidative stress with diabetes. Some investigators have examined levels of ROS or their degradation products, while others have assessed tissue and blood levels of micronutrient antioxidants and/or the levels and activities of antioxidant enzymes in experimental animals and in individuals afflicted with diabetes. While it has been fairly accepted that oxidative stress may play a role in the etiology of type 1 diabetes [4,8,9], it is presently not clear that it plays any role in the pathogenesis of type 2 diabetes. Previous studies had suggested that oxidative stress is a consequence of type 2 diabetes and may be primarily involved in the development of secondary complications of the disease [10–15]. However, there is a growing body of evidence to show that it 412may actually play a role, even if secondary, in the pathogenesis of the disease [1–3,6,7,16–20]. In this chapter, we will review the literature to determine the relationship between oxidative stress and type 2 diabetes, with particular attention to the role played by oxidative stress in the pathogenesis of the disease. We will then determine if there is a valid scientific basis for a beneficial role of antioxidant supplementation in the prevention and as adjunct therapy for glycemic control in human subjects afflicted with type 2 diabetes, as reported in some studies.