Costus Igneus: The Natural Insulin Plant Explained

General features: Costus igneus (CI), also known as Chamaecostus cuspidatus, is a herbaceous perennial commonly called fiery costus, spiral flag, or, especially in India, the ‘insulin plant’ because of its reported antidiabetic effects [1]. In Hindi, it is known as Jarul, in Bengali as Piasal, and in Sanskrit as Asana or Bandhukapushpa. CI actually belongs to the Costaceae family and the Chamaecostus genus. It has large, fleshy, smooth, dark green leaves with a slight purple underside and bears cone-shaped orange flowers. Native to Brazil, the plant is widely used in traditional medicine for its claimed antidiabetic roles, attributed to corosolic acid, a pentacyclic triterpene found in its leaves [2].

The leaves are arranged spirally around the stem, giving the plant a distinctive appearance. It grows to about 2 feet tall and bears yellow flowers about 1.5 inches in diameter. These flowers bloom in warm months in cone-shaped clusters at the branch tips. The plant is cultivated mainly in Himalayan regions such as Kashmir for its roots, which also show antioxidant, anti-inflammatory, and blood sugar-lowering properties [3]. CI is closely related to ginger and was formerly classified in the Zingiberaceae family [4]. Its flowers are bright and showy, with a prominent petal-like structure called the labellum, and its foliage is aromatic and spicy like that of ginger [5]. Although commonly called the insulin plant, CI should be used only as a supplement for prediabetes or type 2 diabetes, not as a replacement for insulin or other antidiabetic medications. Studies suggest that it may help lower blood sugar in some individuals, making it a possible supportive aid in diabetes management. However, it may also cause side effects such as dizziness and nausea, and can significantly reduce blood sugar when combined with other antidiabetic drugs. Its leaves are popularly associated with the saying, “a leaf a day keeps diabetes away” [6]. The plant is edible, and its leaves, roots, and stems are used as needed. In many regions, the fresh leaves are chewed directly or chopped, dried, and used to make tea. The flowers are also eaten and have a sweet taste [7].

Traditional or folk medicinal uses: Recently, CI has gained considerable attention, especially for its potential antidiabetic effects. In the Philippines, it is widely used as an herbal remedy for diabetes. In Siddha medicine, a traditional healing system from southern India that emphasizes balance of the body, mind, and spirit through herbs, diet, and lifestyle, CI is believed to help prevent or manage diabetes. Tribes in the Kolli Hills of Tamil Nadu commonly chew the leaves or take ½ gram of dried leaf powder twice daily to manage the condition [8]. In Mizoram, India, decoctions made from the leaves or roots are used to help prevent diabetes and lower blood sugar levels. In Sikkim, the leaves and roots are also used to treat asthma, bronchitis, fever, intestinal worms, and diabetes [9,10]. In Mexico, the plant has additionally been used for renal disorders [8].

History of the insulin plant: CI is native to tropical regions, including Central and South America and India. Historically, it was used in Mayan and Mexican folk medicine to treat renal disorders. Long before it became widely known as the “insulin plant,” indigenous healers in several South American countries prepared teas or infusions from its aerial parts to address kidney problems [8]. The plant was later introduced to India by South American traders. It was quickly adopted by herbalists and Ayurvedic practitioners because chewing its leaves was believed to lower blood glucose levels. It soon became popular in South India not only as an ornamental plant but also as a dietary supplement for people with diabetes to help manage blood sugar levels. Compounds isolated from the leaves include terpenoids, flavonoids, and alkaloids. More recent studies have also identified a protein that is structurally different from, but functionally similar to, insulin and appears to have an oral hypoglycemic effect [11].

Phytochemicals and their activities: CI contains many bioactive compounds, including flavonoids, terpenoids, steroids, phenolics, and fatty acids [12]. Mature leaves contain flavonoids, terpenoids, steroids, and fatty acids such as hexadecanoic, 9,12-octadecanoic, and tetradecanoic acids, along with ethyl oleate, oleic acid, and squalene. The stem is rich in lupeol and stigmasterol, the rhizome contains quercetin, diosgenin, and sapogenin, and the roots mainly contain tannins, terpenoids, and alkaloids [13]. CI also provides protein, iron, and antioxidants such as ascorbic acid, α-tocopherol, and β-carotene. Its leaves have the highest fiber content (about 21.2%) and contain notable minerals including K, Ca, Cr, Mn, Cu, and Zn [8]. In the leaf ether fraction, the main component is bis-(2`-ethylhexyl)-1,2-benzenedicarboxylate (59.04%), with smaller amounts of α-tocopherol and ergostanol.

Diosgenin, a triterpenoid, lowers blood glucose in diabetic rats by stimulating pancreatic β-cells, promoting insulin release, and helping repair tissue damage. It also inhibits diabetes-related enzymes and reduces hyperglycemia and hypercholesterolemia [14]. Corosolic acid, often described as “plant-derived insulin,” may aid diabetes management by increasing glucose uptake, improving insulin sensitivity, and slowing intestinal carbohydrate absorption. It also promotes GLUT4 translocation to the cell surface and downregulates enzymes involved in glucose production [15]. β-sitosterol increases fasting plasma insulin, improves glucose-stimulated insulin secretion, and enhances glucose uptake in adipocytes, thereby promoting adipogenesis in differentiating preadipocytes [16]. Flavonoids such as quercetin in CI enhance glycogen synthesis, increase antioxidant enzyme activity, reduce intestinal glucose absorption by inhibiting GLUT2, and improve both insulin secretion and insulin-mediated glucose uptake [17]. Epigallocatechin and epigallocatechin gallate reduce blood glucose by inhibiting α-glucosidase, helping limit postprandial blood sugar spikes [18]. Stigmasterol promotes cholesterol efflux, reduces LDL-induced release of pro-inflammatory cytokines, and protects against glucolipotoxicity-induced β-cell dysfunction, thereby potentially helping prevent cholesterol-related β-cell failure [16,19,20]. Pentacyclic triterpenes, especially oleanolic and ursolic acids, inhibit α-glucosidase and α-amylase, thereby reducing intestinal carbohydrate absorption [21]. Aqueous and alcoholic extracts also show dose-dependent hypolipidemic effects by lowering serum cholesterol, triglycerides, and LDL [21]. In addition, CI extracts exhibit significant antioxidant, diuretic, antimicrobial, and anticancer activities [8].

Diosgenin, a triterpenoid, lowers blood glucose in diabetic rats by stimulating pancreatic β-cells, promoting insulin release, and helping repair tissue damage. It also inhibits diabetes-related enzymes and reduces hyperglycemia and hypercholesterolemia [14]. Corosolic acid, often described as “plant-derived insulin,” may aid diabetes management by increasing glucose uptake, improving insulin sensitivity, and slowing intestinal carbohydrate absorption. It also promotes GLUT4 translocation to the cell surface and downregulates enzymes involved in glucose production [15]. β-sitosterol increases fasting plasma insulin, improves glucose-stimulated insulin secretion, and enhances glucose uptake in adipocytes, thereby promoting adipogenesis in differentiating preadipocytes [16]. Flavonoids such as quercetin in CI enhance glycogen synthesis, increase antioxidant enzyme activity, reduce intestinal glucose absorption by inhibiting GLUT2, and improve both insulin secretion and insulin-mediated glucose uptake [17]. Epigallocatechin and epigallocatechin gallate reduce blood glucose by inhibiting α-glucosidase, helping limit postprandial blood sugar spikes [18]. Stigmasterol promotes cholesterol efflux, reduces LDL-induced release of pro-inflammatory cytokines, and protects against glucolipotoxicity-induced β-cell dysfunction, thereby potentially helping prevent cholesterol-related β-cell failure [16,19,20]. Pentacyclic triterpenes, especially oleanolic and ursolic acids, inhibit α-glucosidase and α-amylase, thereby reducing intestinal carbohydrate absorption [21]. Aqueous and alcoholic extracts also show dose-dependent hypolipidemic effects by lowering serum cholesterol, triglycerides, and LDL [21]. In addition, CI extracts exhibit significant antioxidant, diuretic, antimicrobial, and anticancer activities [8].

Toxicity: No significant toxicity is noted even at high extract doses of 5000 mg/Kg body weight or when using fresh leaves, stems, or flowers [8].

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