CHAPTER TWO
LITERATURE REVIEW
2.0 Introduction
This chapter presents a review of relevant literature aligned with the study’s objectives, covering the global and regional prevalence of diabetes, identification of medicinal plants with anti-diabetic properties, and methods used for testing plant extracts for anti-diabetic activity.
2.1 Prevalence of Diabetes
Non-communicable diseases (NCDs) account for over 44% of deaths and 80% of outpatient visits globally. Among these, diabetes is a major concern, alongside chronic obstructive pulmonary disease (COPD) at 43% and cardiovascular diseases (CVD) at 40% (Marmot & Bell, 2019). Factors such as sedentary lifestyles, rapid urbanization, poor dietary habits, and improvements in maternal and child health have shifted disease trends toward NCDs (Bigna & Noubiap, 2019). Common risk factors include tobacco use, alcohol consumption, and smoking (Deventer, 2019).
According to the International Diabetes Federation (IDF), 537 million adults aged 20–79 had diabetes worldwide in 2021, with projections indicating an increase to 642 million by 2045 (Katzmarzyk et al., 2022). The global prevalence stands at 8.5%, with Type 2 diabetes comprising about 90% of all cases, while the remaining 10% include Type 1 and other types (Drapkina et al., 2022). Notably, low- and middle-income countries host approximately 80% of all cases, with the highest numbers recorded in China, India, and the USA (Fitipaldi & Franks, 2023).
In Africa, urbanization and lifestyle changes are contributing to rising diabetes rates. In 2021, 19.4 million people in Africa were diabetic, and this is projected to reach 47 million by 2045 (Momma et al., 2022). While the regional prevalence (3.3%) is below the global average, some countries like Mauritius and Seychelles report rates as high as 20% (Armocida et al., 2022). Lack of diagnosis and treatment is common, leading to severe complications like blindness and amputations (Khan et al., 2012).
Type 1 diabetes mellitus (T1DM), which accounts for 5–10% of all cases, results primarily from autoimmune destruction of pancreatic β-cells (Munekawa, 2021). If untreated, T1DM can manifest as ketoacidosis (Subir, 2020). This condition involves a catabolic state characterized by absent insulin, elevated plasma glucagon, and β-cell non-responsiveness, necessitating external insulin administration. Around one-third of susceptibility to immune-mediated T1DM is genetic, while two-thirds are environmental (Aminian, 2019). A milder form, known as latent autoimmune diabetes of adults (LADA), retains some β-cell function initially but progresses over time (Wang et al., 2022).
In Korea, diabetes prevalence among those aged 30 and above increased from 2.23 million in 2006 to 4.94 million in 2018, with notable growth among individuals in their 20s and 30s (Saeedi, 2020). Young individuals often exhibit worse glycemic control, severe insulin resistance, and rapid β-cell decline, making early intervention crucial (Sinclair, 2020).
Environmental factors—such as occupation, behavior (smoking, alcohol, inactivity), obesity, and poor diet—contribute significantly to diabetes in youth, more so than genetics (Bahar et al., 2020). A BMI over 30 kg/m² increases diabetes risk sevenfold (James et al., 2020).
In East Africa, Kenya and Uganda have reported diabetes prevalence rates of 2.2% and 1.5%, respectively, in 2021 (Barasa & Mmusi, 2021; Ssekamatte et al., 2021). However, the true figures may be higher due to undiagnosed cases, with rates expected to rise due to urbanization and lifestyle transitions.
