Banaba

Banaba (Lagerstroemia speciosa L.)

1. Identity

Botanical and Chemical Names

Lagerstroemia speciosa L. (family Lythraceae) is commonly known as banaba or crepe myrtle. The species is also known as "Pride of India." Other common names include Queen's Crape-myrtle, Giant Crepe Myrtle, and Pride of India. The term "banaba" most specifically refers to the leaves of the tree and to preparations derived from them, and is the name by which the plant is universally known in the Philippines.

Natural Source and Morphology

Lagerstroemia speciosa is a type of crepe myrtle that grows in India, the Philippines, and Southeast Asia. Banaba is a medium to large deciduous tree, reaching heights of 15–25 meters in native tropical regions like South India, Southeast Asia, and the Philippines. Its wood is able to withstand drought, fire, and even termites, while its pretty purple and mauve flowers blossom from April to June and produce round, green fruit. The leaves are arranged opposite, or almost opposite, to one another. They are simple, elliptical, and oblong with entire margins. The leaf blade is 5–10 cm long, and has prominent veins, especially on the dorsal side. Mature leaves are leathery in texture.

Common Forms and Preparations

Lagerstroemia speciosa grows in India, the Philippines, and Southeast Asia; the leaves are used as medicine. Ayurvedic tradition typically uses dried leaves—crushed into teas, powders, or ethanolic extracts. Commercially, banaba is available in several standardized forms. Recently, GlucosolTM and Banabamin herbal products have been developed from Lagerstroemia speciosa as anti-diabetic preparations. The antidiabetic activity of an extract standardized to 1% corosolic acid (Glucosol) has been demonstrated in randomized clinical trials; subjects received a daily oral dose, with dosages of 32 and 48 mg for 2 weeks showing significant reductions in blood glucose levels. A soft gel capsule formulation showed a 30% decrease in blood glucose levels compared to a 20% drop seen with dry-powder-filled hard gelatin capsules (P<0.001), suggesting that the soft gel formulation has better bioavailability than a dry-powder formulation.

2. Traditional and Historical Use

Philippines and Southeast Asia

Banaba (Lagerstroemia speciosa L.) extracts have been used for many years in folk medicine to treat diabetes, with the first published research study being reported in 1940. Lagerstroemia speciosa, the leaves of which are called banaba, is a common tree in the Philippines; for many years, people of that country have used a decoction of its leaves as an aid in lowering blood glucose. In the Philippines, the dried and shredded banaba leaves are used as a treatment for diabetes and kidney disease. The leaves of Lagerstroemia speciosa, a Southeast Asian tree more commonly known as banaba, have been traditionally consumed in various forms by Filipinos for treatment of diabetes and kidney-related diseases.

Banaba has been used in folk medicine to treat diabetes in various parts of the world, especially in the Philippines and Southeast Asia. Folkloric use of banaba leaf decoctions for diuretic and purgative purposes, and of the bark and root parts for stomach ailments, has also been recorded. A leaf poultice is used to relieve malarial fever and is also applied on cracked feet. Banaba fruit and leaves have many medicinal properties and are used to treat urinary tract infection, diabetes, diarrhea, and stomach aches.

The leaves of the tree were eaten as a vegetable or steeped into a tea for ingestion. Filipinos consume the leaves of Lagerstroemia speciosa as herbal tea for lowering blood sugar level and reducing body weight.

India and Ayurveda

The leaves of the species have been traditionally used over thousands of years as folkloric treatment by native Indians for illness and ailments, particularly for lowering blood sugar levels and weight loss. The tree's common Indian epithet, "Pride of India," reflects its longstanding presence in the Indian subcontinent. Community gardens in Kerala still cultivate banaba for local Ayurvedic clinics.

Scope of Traditional Use

Banaba (Lagerstroemia speciosa L.) has been used as a folk medicine to treat diabetes in various parts of the world, primarily Southeast Asia. Traditional uses extended beyond blood sugar management: banaba is also recommended for kidney, bladder problems, and hypertension. The first formal scientific investigation of these traditional claims, the first research study evaluating the insulin-like activity of an aqueous extract of dried leaves, was conducted in rabbits and published in 1940.

3. Key Constituents and Active Compounds

Overview of Phytochemistry

L. speciosa consists of several phytoconstituents such as glycosides, flavones, corosolic acid, ellagic acids, triterpenes, and tannins, which are reported to be present in the leaves, stem, flowers, fruit, bark, and roots. Chemical constituents of Lagerstroemia speciosa include corosolic acid, lageracetal, amyl alcohol, ellagic acid, gallic acid, 4-hydroxybenzoic acid, beta-sitosterol, various methyl ellagic acid derivatives, Asiatic acid, alphitolic acid, 6,7-dihydroxycoumarin, amino acids (alanine, isoleucine, alpha amino butyric acid, and methionine), and ellagitannin.

Corosolic Acid

The banaba leaf contains a natural pentacyclic triterpene, corosolic acid (CA, 2α-hydroxyursolic acid), that activates cellular glucose transport and increases cellular glucose uptake, thereby lowering blood glucose concentrations. Corosolic acid, also known as "plant insulin," is a pentacyclic triterpenoid extracted from plants such as L. speciosa. Corosolic acid also exhibits antihyperlipidemic, antioxidant, anti-inflammatory, antifungal, antiviral, antineoplastic, and osteoblastic activities.

Ellagitannins

The ellagitannin Lagerstroemin was identified as an effective component of the banaba extract responsible for its glucose-lowering activity. Valoneaic acid exists as the structural part of the polyphenols, which — like flosin A, reginin A, and lagerstroemin — are characteristic constituents of banaba. Using bioassay-guided separation, valoneaic acid dilactone was isolated from the leaves as a potent α-amylase inhibitor.

From the known studies, researchers conclude that tannin molecules are responsible for the insulin-like glucose transport stimulatory activity of the banaba extract. Gallotannins such as penta-O-galloyl-glucopyranose (PGG) appear to be more potent and efficacious than ellagitannins such as lagerstroemin in insulin receptor binding, receptor activation, and glucose transport induction.

Other Notable Constituents

The chief active components of banaba extract are ellagitannins, corosolic acid, penta-O-galloyl-glucopyranose, and tannic acid. The tannin content of the extract has been measured at about 37% of dry weight. Flower extracts of the species have pharmacological properties including antioxidant and antimicrobial activities, whereas fruit extracts have reported anti-nociceptive, anti-diarrheal, and cytotoxic activities.

4. Mechanisms of Action

Glucose Uptake and Insulin Signaling

The beneficial effects of banaba and corosolic acid with respect to various aspects of glucose and lipid metabolism appear to involve multiple mechanisms, including enhanced cellular uptake of glucose, impaired hydrolysis of sucrose and starches, decreased gluconeogenesis, and the regulation of lipid metabolism. These effects may be mediated by PPAR and other signal transduction factors.

The primary mechanism involves the facilitation of the translocation of the glucose transporter type 4 (GLUT4) to the cellular membrane, which mirrors the action of insulin. Corosolic acid may act as an insulin sensitizer, enhancing insulin receptor B phosphorylation indirectly by inhibiting certain nonreceptor protein tyrosine phosphatases. Corosolic acid may also enhance GLUT4 glucose transporter processing of glucose uptake into muscle cells. Another study reported that corosolic acid inhibited gluconeogenesis by increasing the production of the gluconeogenic intermediate fructose-2,6-bisphosphate in isolated hepatocytes.

At a single dose of 10 mg/kg in genetically diabetic (KK-AY) mice, corosolic acid significantly reduced blood sugar levels; this effect was shown to be associated with an increase in the muscle glucose transporter GLUT4. In a subsequent study, a single dose of 2 mg/kg corosolic acid reduced blood sugar levels for up to 2 weeks, supporting the hypothesis that corosolic acid improves glucose metabolism by reducing insulin resistance.

Alpha-Amylase and Sucrase Inhibition

Using bioassay-guided separation, valoneaic acid dilactone was isolated from the leaves as a potent α-amylase inhibitor. In animal studies, an oral dose of 10 mg/kg corosolic acid suspended in water inhibited the intestinal hydrolysis of sucrose but not maltose or lactose, thereby at least in part facilitating the lowering of blood glucose levels.

Signal Transduction

The mechanisms of action involved include enhanced cellular uptake of glucose, impaired hydrolysis of sucrose and starches, decreased gluconeogenesis, and the regulation of lipid metabolism. These activities can be mediated by peroxisome proliferator-activated receptor (PPAR), mitogen-activated protein kinase (MAPK), NF-κB, and other signal transduction factors.

Antioxidant Mechanisms

The antioxidant and free radical scavenging activities of banaba were demonstrated for an aqueous extract in in vitro free radical generating systems in a concentration-dependent manner. The banaba extract was shown to have potent radical scavenging activity on DPPH radical and superoxide radicals generated by a hypoxanthine-xanthine oxidase system. The extract also inhibited lipid peroxidation in a rat liver homogenate system.

5. Scientific Evidence by Area of Use

5.1 Blood Glucose Regulation and Diabetes

Human / Clinical Evidence

Studies have been conducted in various animal models, human subjects, and in vitro systems using water-soluble banaba leaf extracts, corosolic acid, and ellagitannins. Banaba extracts have been used for many years in folk medicine to treat diabetes, with the first published research study being reported in 1940.

Judy et al. (Glucosol RCT): The antidiabetic activity of an extract from the leaves of Lagerstroemia speciosa standardized to 1% corosolic acid (Glucosol) was demonstrated in a randomized clinical trial involving Type II diabetics (NIDDM). Subjects received a daily oral dose of Glucosol; dosages of 32 and 48 mg for 2 weeks showed a significant reduction in blood glucose levels. A soft gel capsule formulation showed a 30% decrease in blood glucose levels compared to a 20% drop seen with dry-powder-filled hard gelatin capsules (P<0.001), suggesting that the soft gel formulation has better bioavailability than a dry-powder formulation.

Ikeda et al. (Banabamin crossover trial): A proprietary product called Banabamin in tablet form containing an aqueous extract of banaba was used; this product also contained extracts of green tea, green coffee, and Garcinia. Twenty-four human subjects with mild type 2 diabetes were given three tablets three times daily. A 13.5% average decrease in blood glucose levels was reported, and no adverse effects were observed. The constituents in the product responsible for the antidiabetic effect were not determined.

Ikeda et al. (1-year open-label safety study): Ikeda et al. also conducted a 1-year open-label safety and efficacy study on 15 subjects, administering 100 mg tablets daily of a water-soluble banaba extract. The extract was not standardized, and the constituent(s) responsible for the antidiabetic effects was not determined. A significant decrease (16.6%) in fasting blood glucose levels was observed in individuals with fasting blood glucose levels greater than 110 mg/dL. After both 6 months and 1 year, significant improvements were observed with respect to glucose tolerance and glycated albumin. The banaba extract did not cause hypoglycemia. No changes in hematological or biochemical characteristics and no adverse effects were observed over the 1-year course of the study.

Fukushima et al. (corosolic acid OGTT crossover trial): In this study, 31 subjects were orally administered 10 mg corosolic acid (CRA) or a placebo, on different occasions, in a capsule 5 minutes before a 75-g oral glucose tolerance test (OGTT) in a double-blind crossover design. Nineteen subjects had diabetes, seven had impaired glucose tolerance, one had impaired fasting glucose, and four had normal glucose tolerance. There were no significant differences in plasma glucose levels before and 30 minutes after administration. CRA treatment subjects showed lower glucose levels from 60 minutes until 120 minutes, reaching statistical significance at 90 minutes.

Postprandial glucose study (2006, nondiabetic subjects): In a study, 12 nondiabetic subjects with a baseline blood glucose level of 104 mg/dL were given a soft gel capsule daily for 2 weeks containing 10 mg corosolic acid as a banaba extract standardized to 18% corosolic acid. A 12% decrease in fasting as well as 60-minute postprandial blood glucose levels was observed after 2 weeks of administering the product.

Randomized crossover trial (2022, impaired fasting glucose): Corosolic acid improves glucose metabolism in diabetics and prediabetics; non-diabetic middle-aged men (n = 14) with impaired fasting glucose tolerance (mean age 51.7 years; fasting blood glucose 6.0 mmol/L) underwent an oral glucose tolerance test after taking 1 mg/day corosolic acid or placebo for 2 weeks in a randomized double-blind crossover trial.

López-Murillo et al. (metabolic syndrome RCT, 2022): To evaluate the effect of banaba on metabolic syndrome (MetS), insulin sensitivity, and insulin secretion, a randomized, double-blind, placebo-controlled clinical trial was carried out in 24 patients with MetS diagnosed according to the International Diabetes Federation criteria. Body weight, waist circumference, and blood pressure were evaluated. Fasting plasma glucose and insulin concentrations were measured every 30 minutes during 2 hours after a 75-g dextrose load. Lipid profile was determined before and after the intervention. Twelve patients received banaba (500 mg) twice a day, before breakfast and dinner for 12 weeks; the remaining 12 received placebo at the same dosage. After randomization, 12 patients were assigned to receive banaba extract 500 mg, standardized to 1.13% corosolic acid (MonoHerb, India) before breakfast and dinner for 12 weeks.

Summary and Evidence Strength

The above clinical studies demonstrate that banaba extract, banaba extract standardized to corosolic acid, and corosolic acid itself decrease fasting as well as postprandial blood glucose levels in humans. A decrease in blood glucose levels has been observed within 2 hours of dosing, and the decrease is typically in the range of 10–15%, although a decrease of 30% has been reported. Additional human efficacy and safety studies are warranted, particularly studies assessing the dose- and time-dependent effects of corosolic acid or corosolic acid-standardized banaba extracts and ellagitannins alone or in combination with other ingredients. Investigations are needed to clearly define and understand the roles and importance of corosolic acid and related pentacyclic terpene acids relative to the ellagitannins present in banaba. Overall, the existing body of human evidence is preliminary to moderate in strength: trials are small (typically fewer than 30 subjects), short in duration (usually 2–12 weeks), and many have employed multi-ingredient preparations, making it difficult to isolate banaba's individual contribution. People use banaba for prediabetes, diabetes, and other conditions, but there is no good scientific evidence to support these uses according to the WebMD/Natural Medicines classification framework, reflecting the limited size and robustness of the available trials.

5.2 Metabolic Syndrome and Lipid Metabolism

Banaba extract, corosolic acid, and other constituents may be beneficial in addressing the symptoms associated with metabolic syndrome, as well as offering other health benefits. Corosolic acid also exhibits antihyperlipidemic and antioxidant activities. In animal studies, banaba decreased hepatic lipid content and body weight and inhibited glucose elevation and plasma total cholesterol. Banaba extract also inhibited adipocyte differentiation in preadipocytes.

The 2022 López-Murillo et al. RCT evaluated lipid outcomes alongside glycemic parameters in patients with metabolic syndrome (see section 5.1 for study design). Banaba leaf extract, rich in corosolic acid and ellagitannins, has shown promising results in improving glycemic control; as observed in preclinical studies, both banaba extract and corosolic acid exert insulin-sensitizing, glucose-lowering, and lipid-lowering properties. The evidence for lipid-lowering effects in humans currently derives mostly from animal and in vitro studies, and from trials in which banaba was one component of a multi-ingredient nutraceutical formulation; isolated human evidence is insufficient to draw firm conclusions.

5.3 Antiobesity Effects

Both water and methanol extracts of banaba were found to stimulate glucose uptake by 3T3 adipocytes; the extracts also inhibited adipocyte differentiation induced by insulin. Research on leaf extracts reveals anti-obesity activity in preclinical models. A growing body of evidence involving animal and human studies as well as in vitro systems indicates that banaba leaf extracts exert antidiabetic and antiobesity effects. However, dedicated human trials focusing specifically on body weight or adiposity as primary endpoints are lacking, and existing clinical data for weight management are insufficient to support robust conclusions.

5.4 Antioxidant Activity

The antioxidant and free radical scavenging activities of banaba were demonstrated for an aqueous extract in in vitro free radical-generating systems in a concentration-dependent manner. The banaba extract was shown to have potent radical scavenging activity on DPPH radical and superoxide radicals generated by a hypoxanthine-xanthine oxidase system. The extract also inhibited lipid peroxidation in a rat liver homogenate system. PGG possesses many other health-beneficial bioactivities, including anticancer, anti-inflammation, anti-virus (anti-HIV, anti-SARS), and antioxidant activity in in vitro systems. No controlled human trials have specifically examined banaba's antioxidant effects as a primary outcome. Evidence is limited to in vitro and animal data.

5.5 Urinary Tract and Kidney Health

The leaves of banaba have been traditionally consumed in various forms by Filipinos for treatment of diabetes and kidney-related diseases. Folkloric use of banaba leaf decoctions for diuretic purposes has been recorded. The current literature describes pharmacological effects of Lagerstroemia speciosa that include diuretic and nephroprotective effects, though these have been established primarily in preclinical systems. No rigorous human clinical trials have evaluated banaba specifically for urinary tract or kidney outcomes.

5.6 Anti-Inflammatory Activity

The application of corosolic acid attenuates cardiomyocyte hypertrophy in vitro by activating autophagy, and in mice, corosolic acid exhibits anti-inflammatory and anti-arthritic activity. Pharmacological effects attributed to Lagerstroemia speciosa in the literature include anti-inflammatory and analgesic activity. As with antioxidant activity, the anti-inflammatory evidence for banaba in humans is currently absent; available data are from animal models and in vitro studies only.

5.7 Other Investigated Activities

The pharmacological literature on Lagerstroemia speciosa also documents antimicrobial, anticancer, antiviral, thrombolytic, cardiovascular, central nervous system-related, xanthine oxidase inhibitory, and hepatoprotective activities. Protective effects of banaba leaf methanolic extracts were observed in C57BL/6 mice with dextran sulfate sodium-induced ulcerative colitis. All of these additional activities are currently supported only by in vitro or animal data, and no human trials have been conducted on these endpoints.

6. Body Systems and Health Areas Associated with Banaba

• Endocrine / Metabolic system: Blood glucose regulation, insulin sensitivity, type 2 diabetes management, metabolic syndrome, lipid metabolism.
• Cardiovascular system: Antihyperlipidemic activity (preclinical); corosolic acid studied for anti-arthritic and anti-inflammatory roles in animal models.
• Urinary / Renal system: Traditional diuretic and kidney-supportive use, nephroprotective preclinical data.
• Adipose tissue / Body weight: Inhibition of adipocyte differentiation in vitro; anti-obesity effects in animal models.
• Gastrointestinal system: Inhibition of carbohydrate-digesting enzymes (α-amylase, sucrase); preclinical data on colitis models.
• Immune / Inflammatory system: Anti-inflammatory, antioxidant, and antimicrobial activities documented in preclinical models.

7. Dosage Forms and Reported Dosages

The following dosages are reported from cited clinical studies only, and are not recommendations.

• Glucosol (1% corosolic acid soft gel): Ten type 2 diabetic subjects were given 32 mg or 48 mg of the product (0.32 and 0.48 mg corosolic acid, respectively) daily for 2 weeks; a 30% decrease in blood glucose levels was reported after 2 weeks.
• Banaba extract standardized to 18% corosolic acid (soft gel): 12 nondiabetic subjects were given a soft gel capsule daily for 2 weeks containing 10 mg corosolic acid as a banaba extract standardized to 18% corosolic acid; a 12% decrease in fasting and 60-minute postprandial blood glucose was observed.
• Corosolic acid capsule (OGTT crossover study): 31 subjects were orally administered 10 mg corosolic acid or a placebo in a capsule 5 minutes before a 75-g OGTT.
• Corosolic acid (impaired fasting glucose crossover, 2022): Non-diabetic middle-aged men with impaired fasting glucose tolerance took 1 mg/day corosolic acid or placebo for 2 weeks.
• Banaba extract 500 mg (metabolic syndrome RCT, 2022): 12 patients received banaba extract 500 mg standardized to 1.13% corosolic acid (MonoHerb, India) before breakfast and dinner for 12 weeks.
• Banabamin tablet (open-label safety study): Ikeda et al. conducted a 1-year open-label safety and efficacy study on 15 subjects, administering 100 mg tablets daily of a water-soluble banaba extract.
• Banabamin (crossover clinical trial): Twenty-four patients with mild type 2 diabetes were enrolled; they were given 3 tablets of Banabamin or placebo three times a day in a crossover design.

8. Safety Considerations and Interactions

General Safety Profile in Clinical Studies

No adverse effects have been observed or reported in animal studies or controlled human clinical trials reviewed by Stohs et al. (2012). The banaba extract did not cause hypoglycemia, and no changes in hematological or biochemical characteristics and no adverse effects were observed over the 1-year course of the open-label study.

Short-Term Safety and Reported Side Effects

When taken by mouth, banaba is possibly safe when used short-term; it has been used safely for up to 2 weeks. There is not enough reliable information to know if banaba is safe to use long-term. Side effects might include dizziness, headache, and upset stomach.

Hypoglycemia Risk

Contrary to the logical expectation that the blood sugar-lowering capacity of banaba would cause low blood sugar (hypoglycemia), 6 clinical trials did not lead to any such effect. Nonetheless, additive pharmacodynamic effects cannot be excluded when banaba is combined with blood-glucose-lowering agents (see interactions below).

Drug Interactions

Antidiabetic medications: Banaba leaf extract may lower blood sugar levels, which can be problematic when combined with antidiabetes drugs like metformin, glimepiride, or insulin; this combination may cause blood sugar to drop too low, leading to hypoglycemia.

NSAIDs / Diclofenac: A single report has suggested that corosolic acid may have been involved in nephrotoxicity and lactic acidosis in a diabetic patient with impaired kidney function who was also taking diclofenac for joint pain. Diclofenac is a nonsteroidal anti-inflammatory drug, and this class of drugs is known to cause renal damage and failure. The role of corosolic acid, if any, is not clear. The use of a drug known for its nephrotoxicity in conjunction with impaired kidney function readily explains the resulting kidney failure. The ability of corosolic acid to inhibit gluconeogenesis could favor lactic acid production. No evidence was provided to specifically demonstrate this possible effect, and no controlled clinical studies have reported nephrotoxicity in diabetic subjects receiving corosolic acid.

Other blood-sugar-lowering herbs: Herbs including fenugreek, garlic, guar gum, and horse chestnut — all of which help lower blood sugar levels — along with diabetic medication, theoretically will have enhanced effects when taken along with banaba. This is a theoretical interaction based on pharmacodynamic reasoning, not confirmed in clinical trials.

Special Populations

Banaba leaf is generally considered safe to consume, though its safety profile is incomplete in pregnant women and children. No controlled data are available on banaba use during pregnancy or lactation, and no pediatric studies have been conducted.

Evidence Gaps and Limitations

There is no safe and effective dose of banaba extract because no sufficiently powered clinical trial has been conducted to find one; only the doses which produced a benefit in existing clinical studies can be discussed. Additional human efficacy and safety studies are warranted, particularly studies assessing the dose- and time-dependent effects of corosolic acid or corosolic acid-standardized banaba extracts and ellagitannins alone or in combination with other ingredients. Most human trials to date have been small (fewer than 30 participants), of short duration (2–12 weeks), and have used varying preparations and standardization levels, making cross-study comparisons difficult. Several key studies used multi-ingredient products, preventing definitive attribution of effects to banaba alone.

References

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