More than 1200 plant compounds have been tested for their ability to lower blood sugar levels. Many have been found to contain chemical components that have hypoglycemic activity (the ability to lower blood sugar) when tested in test tubes or in animal models. However, there is very little research on such compounds using human subjects, and what research does exist is generally not of high quality.
A few herbal remedies for diabetes have been tested in humans and have been found to have mild blood-sugar-lowering properties. These compounds have not had very powerful effects and at this time are not felt to be adequate for the management of diabetes alone. The most promising of these botanicals include bitter melon (Momordica charantia), fenugreek (Trigonella foenum-graecum), gurmar (Gymnema sylvestre), goat's rue (Galega officinalis), bilberry (Vaccinium myrtillus), ginseng (chiefly Panax), nopal (Opuntia streptacantha), and garlic and onion (Allium sativum and Allium cepa).
Bitter melon
Also called bitter gourd, bitter cucumber, balsam pear, karela, and charantin, bitter melon is the most widely used traditional remedy for diabetes. It is commonly used in Asia, especially in India, and in Africa. Bitter melon is frequently eaten as a vegetable and looks like a misshapen, bumpy cucumber. As a treatment for diabetes, it is typically the juice or an extract of the unripe fruit that is used. Dried or powdered forms of bitter melon are not believed to have the same activity.
Several compounds have been isolated from bitter melon that are believed to be responsible for its blood-sugar-lowering properties. These include charantin and an insulin-like protein referred to as polypeptide-P, or plant insulin. It is believed that bitter melon acts on both the pancreas and in nonpancreatic cells, such as muscle cells.
There are no well-designed studies using bitter melon in humans. Most studies have not used controls or placebos, and those that have did not always randomly assign people to treatment groups. These precautions are needed to ensure that the results obtained are real and not merely due to chance. Most of the studies that have been done are short-term studies.
In one study, polypeptide-P isolated from bitter melon was injected (in a manner similar to that used with commercial insulins) into subjects with either Type 1 diabetes or Type 2 diabetes. It decreased blood glucose levels from an average of 305 mg/dl (milligrams per deciliter) before treatment to 168 mg/dl after four hours in subjects with Type 1 diabetes, and from 140 mg/dl to 95 mg/dl after one and a half hours in subjects with Type 2 diabetes. There were no significant changes in the control subjects. The results in subjects with Type 2 diabetes were generally not considered significant, most likely due to the small number of subjects and the variability of bitter melon's effects in different people.
Another small study tested the effect of eating powdered whole bitter melon for one week in people with Type 2 diabetes. Fasting blood sugar levels and blood sugar levels measured after consuming 50 grams of pure glucose (this is called a glucose tolerance test and is commonly used in research studies) were significantly lower after consumption of bitter melon. The average fasting blood sugar level decreased from 248 mg/dl to 155 mg/dl.
Two other studies, which used fresh bitter melon juice, had similar results. One study found that there were "responders," people whose blood sugar levels during a glucose tolerance test were lower after treatment with bitter melon, and "nonresponders," or people for whom the bitter melon did not have any beneficial effects.
Current preparations of bitter melon are generally not standardized, making recommendations for a specific effective dose difficult. Typically, however, 50 to 200 milliliters (about 2 to 5 ounces) per day of the fresh juice; 3 to 15 grams of the dried, powdered fruit; or 300 to 600 milligrams (divided into three separate doses of 100 to 200 milligrams each) of a standardized extract per day have been used.
There are currently no studies that look at the effects of bitter melon over an extended period of time, and there are no studies of bitter melon's safety, though it is commonly consumed as a vegetable in India and is generally believed to be safe. More research is needed before it can be considered as a potential treatment for diabetes.
Bitter melon is a component of some herbal formulas advertised for people with diabetes. If you use the fresh fruit, prepare it with care: A mildly toxic chemical has been isolated from the seeds and the outer rind. There also are reports of toxicity in children and bleeding and contractions in pregnant women, so this plant should be avoided by these populations. Whatever formulation you choose, work closely with your doctor and health-care team. This precaution is important because there is the potential for hypoglycemia when this herb is combined with medicines that lower blood glucose. Positive effects on blood sugar should be noted fairly quickly. If changes are not seen within four weeks, the herb should be discontinued.
Fenugreek
Fenugreek is a common spice that in small concentrations is categorized by the U.S. Food and Drug Administration as "Generally Recognized As Safe." Its seeds or a defatted powder made from the seeds have been used as a treatment for diabetes. Fenugreek is one of the better researched herbal treatments for diabetes, with both human and animal studies suggesting it has hypoglycemic activity. There is also research suggesting that fenugreek may improve blood cholesterol and triglyceride levels. (Triglycerides are a type of fat that circulates in the blood. High levels are thought to increase the risk of heart disease.)
Fenugreek has been found to improve blood glucose levels in both Type 1 and Type 2 diabetes. In one study, subjects with Type 1 diabetes were randomly assigned to receive either defatted fenugreek seed powder or a placebo for 10 days. After the first 10 days, subjects then received the other treatment for another 10 days. Fenugreek significantly decreased fasting blood glucose levels, improved glucose tolerance test results, and decreased blood cholesterol and triglyceride levels. Blood insulin levels did not change with the treatment.
In people with Type 2 diabetes, three studies have demonstrated positive effects of fenugreek on blood glucose and cholesterol levels. All of these studies used placebos and had more than 20 subjects. In the longest study, lasting three months, people with higher initial blood glucose levels did not respond as well as those with lower initial blood glucose levels. In people who had a positive response, average fasting and postprandial (after-meal) blood glucose levels decreased by about 35 mg/dl. This was statistically significant.
Fenugreek seeds are very high in fiber, and it is believed that at least part of fenugreek's effects are achieved because the fiber decreases absorption of dietary carbohydrates. In the study involving people with Type 1 diabetes, the fiber content of the diet containing fenugreek was very high, containing approximately 80 grams of fiber per day. (For comparison, most Americans get less than 15 grams of fiber per day.)
Other compounds believed to contribute to fenugreek's activity include proteins, saponins, and alkaloids. Names you may see listed on herbal supplements include fenugreekine and trigoneline.
The dose of fenugreek used in research studies has varied a great deal—from 5 grams to 100 grams per day—and is generally divided into at least two equal portions. Since the larger amounts would be impossible to consume in a capsule, they have generally been incorporated into foods in the studies. Some herbal supplements designed for people with diabetes include much smaller quantities of fenugreek, often combined with other herbs, in capsule form. Plain dried fenugreek seed powder is also available in capsules, as a bulk powder, and in a chewable wafer form.
Common side effects seen with high doses of fenugreek include diarrhea and upset stomach. It has also been reported that it may decrease blood coagulation, so people using anticoagulant medicines ("blood thinners") or aspirin should use this herb only under the supervision of their doctor. In animals, extracts of fenugreek have been shown to stimulate uterine contractions in late pregnancy, so this herb should not be used by pregnant women. Because of its high fiber content, it may also alter absorption and effectiveness of other medicines taken at the same time. This herb should not be taken at the same time as other medicines.
Gurmar
Gymnema sylvestre leaf has been used as a traditional treatment for diabetes in India. Because chewing the leaf decreases the sensitivity of taste buds to sweet tastes, gymnema has also been called gurmar, which means "sugar destroyer." This effect is reported to last several hours. In people who have had extracts of gymnema applied to their tongue, this decrease in sensitivity to sweets caused a short-term decrease in food consumption. There are no studies that look at the long-term effects of gymnema on appetite, and it is unlikely that consuming gymnema in a capsule or pill would have the same effect.
The active ingredient in gymnema is believed to be a mixture of molecules called gymnemic acids. You may see gymnemic acids listed on the labels of herbal supplements marketed to people with diabetes. Gymnema is believed to act by improving the function of pancreatic beta cells (the cells in the body that make insulin).
In animals with diabetes, gymnema has appeared to help regenerate or increase the number of functional beta cells present in the pancreas, but when gymnema was given to animals that had had their pancreas removed, there was no effect. This suggests that gymnema requires some residual beta-cell function to work. Gymnema may also decrease glucose absorption from food and improve the ability of the body to use glucose for energy.
There is minimal research on gymnema at this time, and the studies there are in humans have not been well designed. One study, which used subjects with Type 2 diabetes, found that consumption of a concentrated extract of gymnema decreased blood glucose levels and blood cholesterol levels. Gymnema also increased blood insulin levels in these people. Another study, using people with Type 1 diabetes, found that long-term consumption of gymnema decreased blood glucose levels, glycosylated hemoglobin (HbA1c) levels, and insulin requirements. These results are intriguing, but gymnema cannot be recommended as a treatment for diabetes until we have better studies and more of them.
A typical daily dose of gymnema is 400 to 600 milligrams of an extract (standardized to at least 24% gymnemic acids), given usually in four 100-milligram doses throughout the day. Gymnema has no known toxic effects, but its safety has not been directly tested, and it should not be taken by children or pregnant or nursing women. Gymnema does not appear to cause hypoglycemia in people who do not have diabetes.
Goat's rue
Goat's rue is another traditional remedy for diabetes, and it has been shown to have hypoglycemic activity in humans. It appears to act in a manner similar to the synthetic drug metformin (brand name Glucophage), an oral hypoglycemic drug used to treat Type 2 diabetes. Metformin lowers blood sugar by decreasing the production of glucose from the liver. Goat's rue may also inhibit glucose absorption from the intestinal tract. In obese animals, dried goat's rue added to the diet led to decreases in body weight and body fat.
However, one of the active ingredients in goat's rue, galegine, when purified is too toxic to be used as a medicine, and there have been reports of poisoning from goat's rue in grazing animals. It is not recommended as a treatment for diabetes at this time due to its potentially toxic effects.
Bilberry
The leaves of bilberry, also known as European blueberry, are reported to contain chromium and have been used as an antidiabetic tea. In animals, extracts of the leaf decreased blood glucose and blood triglyceride levels. The berries are a rich source of antioxidants (compounds that may decrease the risk of heart disease, cancer, and other chronic diseases) and may improve circulation. They have been suggested as a treatment for diabetic retinopathy.
Chronic consumption of bilberry leaf or capsules is not recommended, as it can be toxic. Potential side effects include anemia, severe weight loss, and excitability. Consumption of high doses can be fatal. Bilberry may also interact with anticoagulant medicines, potentially causing increased bleeding.
Ginseng
Ginseng has long been used as a botanical remedy in the Orient. Today, it is also one of the most commonly used herbal supplements in the United States, where it is sold chiefly as an energy booster. Americans spent more than $86 million on ginseng in 1997. However, ginseng supplements have been found to be one of the less reliable supplements on the market. Tests conducted by independent laboratories frequently find little or no ginseng in the supplements, so purchasers of these products need to do their own background research to avoid spending money on "placebo," or inactive, pills.
The term ginseng has been used to refer to more than one plant group. There is the Panax genus, which includes Korean, Japanese, and American ginseng, and there is the Eleutherococcus genus, which includes Siberian ginseng. It is generally felt that the Asian and American ginsengs act similarly, but that Siberian ginseng is not a true ginseng and cannot be used in place of Panax ginseng. The main active ingredients in ginseng comprise a group of molecules called ginsenosides.
There are only a few small studies looking at the hypoglycemic effects of ginseng, and most of the information we have is with Type 2 diabetes. One study did not specify the type of ginseng used but reported decreases in fasting blood glucose levels and HbA1c in people newly diagnosed with Type 2 diabetes on diet therapy only. The second study used American ginseng (Panax quinquefolius) and tested the short-term effect of a large dose of ginseng (3 grams) on blood glucose levels after consuming 25 grams of glucose. In people with diabetes, consuming ginseng 40 minutes before or with the glucose decreased postprandial blood sugar levels. (These results were marginally significant.)
Typical doses vary from 200 to 600 milligrams per day of a standardized extract, taken in one or two equal doses. Ginseng is generally believed to be safe, but side effects of its use include increased blood pressure, excitability, nervousness, headache, insomnia, diarrhea, nausea, and worsening of asthma. Ginseng may also have mild estrogen-like properties, sometimes causing postmenopausal bleeding or amenorrhea, the absence of menses. It may also interact with the medicines digoxin, warfarin, and diuretics, increasing or decreasing their effectiveness.
Nopal cactus
The stem or leaf of nopal cactus has been used in traditional Mexican medicine to treat Type 2 diabetes. Short-term, uncontrolled studies of this herb in humans have measured decreases in blood glucose, blood cholesterol, and triglycerides. The active ingredient in nopal is not known, but researchers hypothesize that fiber from nopal helps to decrease glucose absorption from the intestine, and that other compounds help to increase the effectiveness of insulin.
Most studies use cooked or fresh nopal, but extracts from the fresh plant are also used. A typical dose is 500 grams of fresh or cooked nopal eaten before or with the meal. There are no known risks associated with eating nopal other than those you would find with an increase in fiber from any source.
Garlic and onions
Garlic is one of the top-selling herbal supplements in the United States. It is best known for its potential protective effects in cardiovascular disease. It has been claimed that garlic can decrease blood cholesterol levels, decrease high blood pressure, and decrease the likelihood of blood clots forming, properties that are all beneficial in preventing heart disease. Numerous studies have examined these effects. In general, it appears that garlic does have a positive effect on these risk factors, and the consensus of the scientific community is that more research is needed before garlic can be recommended as a common treatment.
Garlic and onions have also been used as folk medicines to treat diabetes. There is much less research on this potential role of garlic, but a few studies do suggest that it (and onions) may have some mild blood-sugar-lowering properties. It is believed that garlic and onions lower blood sugar levels by decreasing the rate at which insulin is inactivated and degraded by the body, effectively increasing quantities of circulating insulin and decreasing blood glucose levels. Overall, these effects do not appear to be strong enough to warrant use of garlic or onion as a blood-sugar-lowering agent.
Garlic appears to be generally safe and well tolerated when taken as a supplement. Common side effects include mild stomach discomfort and an unusual body odor (even with the "odorless" forms of garlic). The primary safety concern about garlic relates to its ability to decrease blood clotting. In people who take aspirin or anticoagulant therapies, garlic may lead to increased bleeding. People who use these drugs should discuss with their doctor the safety of taking a supplement containing garlic. Garlic supplements should also be discontinued several weeks before surgery to prevent any problems with blood clotting. They should not be used by pregnant women, because they may cause contractions.
The active ingredients in garlic and onions are sulfur-containing molecules. (These compounds are what give garlic and onions their distinctive smell.) There are more than 20 molecules that are believed to contribute to garlic's effects, but the best understood are allicin, also called diallyl disulfide oxide, and APDS, or allyl propyl disulfide. You may see any of these names on garlic supplement labels.
Common doses for blood-sugar-lowering effects are quite high and probably not realistic for the general population. Typical doses used to decrease blood cholesterol levels are 600 to 900 milligrams, in tablet or capsule form, or one to three fresh cloves per day. Look for products that are standardized and list the active ingredient allicin on the label. Heat and acid destroy the active ingredients in garlic and onions, so slow-release forms or enteric-coated forms of supplements may be more effective.
Safe supplement use
Because the safety and effectiveness of the herbal supplements covered in this article are unproved, people who are interested in using them are in a sense acting as human "experiments." They need to approach the treatments they use very carefully, preferably with the guidance and support of their health-care team. If you would like to try an herbal supplement, here are some guidelines to keep in mind:
• Discuss your plans with your primary health-care provider, and ask whether any of the supplements you'd like to try might interact with drugs you currently take or have other negative side effects.
• Do not use herbal preparations if you are pregnant or nursing. The effects of herbs on a fetus or baby are unknown. Do not give children herbal supplements without first consulting their pediatrician.
• If you get your doctor's OK to try herbal supplements, keep a log of all the supplements you are taking and the specific doses you are taking.
• Try only one new supplement at a time so that you can more effectively gauge its effects.
• Follow the dosage guidelines on the supplement label. Do not take more than the recommended dose.
• Monitor your blood sugar levels more frequently, and keep careful records of your numbers. This is the only way to know what effect the supplement is having on your blood sugar levels.
• Pay attention to any symptoms, such as headaches, nausea, rash, or changes in sleep patterns or mood, that may be side effects caused by a supplement. If symptoms persist, stop taking the supplement and see your doctor.
• Store herbal supplements in their original containers with safety seals intact and out of the reach of children. Having the original container is important in case of accidental overdose or side effects.
• Set a time limit for trying a supplement, usually three to six weeks. If it hasn't had any effect within that limit, stop using it.
Herbal remedies are unlikely to replace existing diabetes drug treatments any time soon. It is possible, however, that some will be shown to be effective in helping to control blood sugar levels or as a basis for designing new drug treatments for diabetes.