South African Herbal Teas and Diabetes-Mediated Mitochondrial Dysfunction: Emerging Evidence and Mechanistic Insights

Type 2 diabetes mellitus (T2DM) is a central component of the metabolic syndrome (MetS) and is associated with underlying mitochondrial dysfunction. Disruption of mitochondrial homeostasis impairs cellular energy metabolism and contributes to the overproduction of reactive oxygen species (ROS), leading to oxidative stress, chronic inflammation, and insulin resistance. These mitochondrial abnormalities exacerbate insulin resistance and impair pancreatic β-cell function, thereby accelerating the progression of T2D. Emerging evidence highlights the therapeutic potential of plant-derived biomolecules, particularly polyphenols found in traditional herbal teas, for mitigating oxidative stress and restoring mitochondrial integrity. This review explores the pathophysiological role of mitochondrial dysfunction and oxidative stress in T2D, with a focus on insulin action and β-cell function. We review three South African herbal teas (Rooibos, Honeybush, and Bush tea) and summarize how, through regulation of the oxidoreductase enzyme system, upregulation of endogenous antioxidant enzymes, inhibition of pro-oxidant enzymes, and support of mitochondrial biogenesis, demonstrating promising bioactivity. The review synthesizes current evidence on the herbal tea's key phytochemicals and their proposed mechanisms of action, highlighting their relevance in mitigating redox imbalance and preserving mitochondrial integrity within the context of diabetes. In addition, factors influencing their nutraceutical value, such as phytochemical composition, processing conditions, and bioavailability, are considered in relation to functional food development. By linking their antioxidant and anti-inflammatory properties to mitochondrial protection, this review underscores their potential role as complementary interventions in the management of T2D. Although emerging in vitro and in vivo studies suggest promising bioactivity of the herbal teas, the current evidence base remains limited by a lack of well-controlled human clinical trials.