Bitter melon is a vegetable that is also used medicinally for diabetes. High doses of extract are toxic to animals, especially pregnant ones, and a leaf infusion has caused hypoglycemic coma in children. Cooked fruit appears benign.
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Latin Name
Momordica charantia L.
Family
Cucurbitaceae
Other Common Names
Karela (Hindi), karla (Marathi), parakkachedi (Tamil), susharl (Sanskrit) bitter gourd, balsam-pear, cundeamor (Spanish). In Jamaica, a cultivated form is called carilla, or goo-fah; a smaller wild variant is called cerasee in Jamaica and sorossie in the Dominican Republic.
Description
- Bitter melon is an annual, climbing vine with showy flowers, cultivated throughout the tropics but especially in India, China, East Africa, the Caribbean, Central America, and South America.
- Its warty, cucumber-like fruit, unripe, is eaten as a vegetable and used medicinally for diabetes.
- The name may come from "mordere" (to bite) because of its bitten appearance.
Part Used
Unripe fruit, seeds, aerial parts
Known Active Constituents
- The fruit contains the insulinomimetic proteins P-insulin and V-insulin, the steroidal glycoside charantin (a mixture of sitosterol and stigmastadienol glycosides, also called sterolins), saponins, and cucurbitacin steroidal glycosides called momordicosides and momordicines.
- Also contains acylglucosylsterols, linolenoylglucopyranosylclerosterol, amino acids, and phenolic compounds (1). Momordica antihuman immunodeficiency virus protein, molecular weight 30 kD, is an antiviral protein derived from karela.
Mechanism/Pharmacokinetics
- No human pharmacokinetics data are available.
- Hypoglycemic effects have been demonstrated for charantin, insulinomimetic proteins, and an alkaloid-rich fraction of karela fruit juice.
- Karela appears to inhibit intestinal glucose uptake and may inhibit hepatic gluconeogenesis (2).
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Clinical Trials
- No placebo-controlled trials were identified; there are many uncontrolled trials. The most recent trial, in 100 participants with non-insulin dependent diabetes mellitus (NIDDM), found that consumption of an aqueous suspension of bitter melon fruit reduced both fasting and postprandial glucose levels significantly in 86 participants; 5 experienced reduction in fasting but not postprandial glucose (3).
- Different preparations may have different effects. A study of nine Asians with NIDDM found that 50 mL of an aqueous extract of karela given with a 50-g oral glucose load reduced glucose concentrations of patients with NIDDM by more than 20% within 1 hour; insulin levels were not affected (4). In the same report, daily consumption of fried karela for 8 to 11 weeks did not significantly affect glucose tolerance but did reduce glycosylated hemoglobin.
- Another study compared powdered fruit (5 g t.i.d. × 21 days) in five diabetics with aqueous extract (100 g in 100 mL water q.d.) in seven diabetics. The powdered fruit did not significantly decrease blood sugar from baseline; the aqueous fruit extract, however, significantly decreased blood sugar 54% from baseline (compared with 25% in the powder-treated group) at the 3-week timepoint. The difference between groups was significant. Glycosylated hemoglobin decreased significantly from 8.37 ± 0.39 to 6.95 ± 0.46 (5). Participants were followed for an additional 4 weeks; the hypoglycemic effect increased over time.
- Daily consumption of powdered karela fruit for 7 weeks improved both glucose tolerance and fasting blood glucose levels in eight patients with NIDDM (6).
- In another trial, karela juice significantly improved glucose tolerance in 13 of 18 patients tested (7).
- Powdered karela seed administered orally (amount not reported) significantly reduced postprandial blood sugar values from 350–380 mg% to 150–180 mg% in 20 diabetic patients, including 14 with NIDDM and 6 with insulin dependent diabetes mellitus (IDDM). Headache and increased appetite were reported (8).
- A polypeptide derived from karela called P-insulin or V-insulin, administered subcutaneously, has been reported to cause significant hypoglycemic effects in nine diabetics (9); another similar study found an effect in 11 IDDM patients but no effect in 8 NIDDM patients (10).
Animal/In Vitro
- Diabetes
- Diabetes studies in rabbits, rats, and mice have demonstrated hypoglycemic effects of karela fruit, juice, or extract, but results have not been entirely consistent. One study of rats found that fruit or seed extract improved glucose tolerance in diabetic animals but that chronic administration of fruit extract was lethal (11). Fasting blood sugar was not affected in normal or streptozocin-diabetic rats.
- The development of cataracts was delayed in karela treated streptozotocin-diabetic rats (5).
- In vitro studies of fruit extract have found stimulation of insulin release from isolated pancreatic islet cells. Insulin-like activity including increased glucose uptake into muscle, stimulation of lipogenesis, and inhibition of lipolysis on tissue preparations has been demonstrated in vitro (1).
- Cancer
- Topical application of karela peel reduced 9,10 dimethyl-1,2-benzanthracene (DMBA)-induced papillomas in mice (seed and whole fruit extract were much less effective) (12). In human breast cancer-bearing SCID mice, MAP30, an antiretroviral protein isolated from karela (10 µg/injection every other day × 10 injections), significantly increased survival (13).
- Other effects
- Karela has been shown to lower cholesterol in normal rats (14). Some analgesic and antiinflammatory effects have been demonstrated in animals (1).
- Antiviral effects
- MAP30 is active against HIV and herpes simplex virus (HSV) (including acyclovir-resistant strains) (15). Sperm are not affected even by very high doses of MAP30 (1,000 times the maximum effective concentration), raising the possibility that this compound could be used in nonspermicidal vaginal microbicides (16).
Other Claimed Benefits/Actions
- Tonic
- Emetic
- Laxative
- Colds, other viral infections
- Fever
- Gastroenteritis
- Tumors
- Abortifacient
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Q: The animal toxicity information is not reassuring. Is this herb dangerous?
A: Bitter melon appears to have very toxic effects in pregnant animals. No reports of uterine rupture or hepatotoxicity have been reported in humans, but karela does have a reputation as an abortifacient and it makes sense not to use it during pregnancy.
It is true that most vegetables seem more benign than this herb. Lack of human adverse effects may be due to species differences in susceptibility or perhaps to the inactivation of toxic compounds by heat, because karela is not eaten raw. It may also have to do with dose; bitter melon is not consumed as a staple and is often used as one of several ingredients in a dish. There is no danger in its traditional food uses, but bitter melon clearly has pharmacologic effects, and it is unknown whether long-term daily intake of karela in the form of powder or juice is safe.