Pathophysiological Role and Therapeutic Potential of Vitamin C in Metabolic Syndrome and Type 2 Diabetes Mellitus

Recently, a growing interest has been focused to the role of vitamin C in chronic diseases. Type 2 Diabetes Mellitus and the Metabolic Syndrome are complex, chronic disorders intrinsically linked by a common underlying element, such as chronic low-grade inflammation and excessive oxidative stress. Vitamin C, or ascorbic acid, is an essential water-soluble micronutrient and a highly potent non-enzymatic antioxidant that is critical for scavenging reactive oxygen species and maintaining cellular redox balance. It represents a cofactor for many enzymes, being involved in many biological functions, such as normal immune system functioning, catecholamine metabolism, dietary iron absorption, and collagen biosynthesis. Individuals with type 2 diabetes mellitus and metabolic syndrome frequently exhibit lower circulating and dietary vitamin C levels compared to healthy controls, a deficiency that may be associated with disease-related inflammation and higher body weight. In this sense, it has been shown that vitamin C improves skeletal muscle insulin sensitivity in experimental settings and modulates critical functions like vascular endothelial health. However, this potential is challenged by the fact that chronic hyperglycemia can interfere with the active cellular uptake and transport of vitamin C, potentially leading to relative intracellular deficiency in diabetic patients regardless of intake. It is interesting to note that different studies have demonstrated an inverse relationship between vitamin C concentrations and the prevalence of metabolic syndrome and type 2 diabetes. Vitamin C supplementation in people with diabetes and metabolic syndrome has controversial effects. While several studies indicate a significant reduction in fasting blood glucose or HbA1c, others revealed no significant effect on insulin resistance. This review aims to explore the pathophysiological role and therapeutic potential of vitamin C in type 2 diabetes and metabolic syndrome.