Polyhydroxylated piperidines and their derivatives are widely recognized for their diverse biological activities. Among these, 1-deoxynojirimycin (DNJ), also referred to as an azasugar, is a naturally occurring bioactive compound present in mulberry leaves. Chemically identified as C₆H₁₃NO₄, DNJ is also known by the name moranoline. In addition to plant sources, it can be synthesized by certain microorganisms, including species of Streptomyces and Bacillus. Within mulberry plants, DNJ is distributed in different parts such as leaves, roots, and stems, although its concentration is highest in the leaves. Various analytical techniques are available to determine DNJ levels, with High-Performance Liquid Chromatography (HPLC) coupled with fluorescence detection being one of the most reliable methods. DNJ has attracted considerable attention due to its wide range of biological and therapeutic properties. It functions as a potent α-glucosidase inhibitor, thereby helping to regulate postprandial blood glucose levels by interfering with carbohydrate digestion. For optimal benefits in humans, regular intake of DNJ is generally recommended. Beyond its role in glucose metabolism, DNJ has been associated with multiple pharmacological effects, including reduction of oxidative stress, and potential benefits in managing conditions such as diabetes, obesity, cancer, and aging. Among different mulberry species, the leaves of white mulberry (Morus Alba) are particularly rich in DNJ. The concentration is reported to be around 0.1% on a dry weight basis, equivalent to approximately 100 mg per 100 g. The estimated effective intake for humans is about 10 mg per 60 kg body weight. Due to its relatively low natural abundance, developing efficient extraction methods is important for its use in food and pharmaceutical applications. This review therefore emphasizes the physiological actions and bioavailability of DNJ.