Diabetes affects an estimated 21 million Americans and takes a staggering toll on health, with complications such as heart disease, high blood pressure, kidney disease, blindness, nerve damage and sexual dysfunction. Another 54 million people have pre-diabetes (slightly elevated blood sugar), a condition that puts them at risk for developing diabetes.1
Most diabetics—90 percent to 95 percent—have type 2 diabetes, in which the pancreas still produces insulin but the body's cells are resistant to its effects. About 57 percent of adults with diabetes take oral medications, which can have side effects ranging from nausea, diarrhea and headache to liver failure and respiratory infections, according to the American Diabetes Association. Various supplements have been studied for their ability to help control blood-sugar levels and prevent type 2 diabetes. Here is a review of some of the most talked about and best-studied natural approaches to treating and preventing type 2 diabetes.
The fruits, seeds and leaves of bitter melon (Momordica charantia) are used as a traditional anti-diabetes remedy in Asia, Africa and South America.2 In research, mostly conducted in India, the herb has demonstrated hypoglycemic effects in both normal and diabetic rats, as well as in patients with type 2 diabetes.3,4,5 The active components of bitter melon are thought to be structurally similar to animal insulin and may have an antioxidant effect.4,6 One animal study found bitter melon to be as effective in lowering blood glucose as an oral hypoglycemic drug.7 However, in another study, in which rats were treated with freeze-dried bitter melon powder for six weeks, no beneficial effects on blood sugar were observed.8
Four clinical trials have reported bitter melon juice, fruit and dried powder have a moderate hypoglycemic effect, but none were randomized or double blind.6 In one trial that was randomized and controlled, 40 patients with newly diagnosed or poorly controlled type 2 diabetes took 3 g a day of a preparation containing bitter melon in addition to their current therapy; no significant changes in fasting blood-glucose levels were noted after treatment.9 Other studies have used a wide variety of preparations and doses, ranging from 3 1/2 oz of bitter melon juice 30 minutes before the beginning of a glucose tolerance test, to 5 g of dried fruit powder three times a day, with widely varying results.6 Some people suggest that the different results are likely due to variations in the plant part used, as well as method of preparation. Though the exact mechanism is not clear, bitter melon's effects may be related to its structural similarity to insulin. It may also stimulate increased insulin secretion from the pancreas.6 Among supplements commonly used to treat diabetes, bitter melon is associated with the greatest number of adverse effects, including severe hypoglycemic reactions, headaches and reduced fertility in animals.6
Chromium is an essential mineral required for normal carbohydrate metabolism and a co-factor for insulin. Both animal and human studies have shown that chromium can improve insulin sensitivity and help regulate blood-sugar levels.10,11,12 More than 40 human clinical studies have tested the effects of different chromium compounds on insulin resistance and risk factors associated with type 2 diabetes. Chromium picolinate is the most studied form.
In a recent review of 15 clinical studies, researchers found that 13 studies showed significant improvement in at least one measure of blood-sugar control after treatment with chromium picolinate.13 In a 2006 clinical study, a supplement containing chromium picolinate and biotin significantly improved blood sugar levels after eating.14 In the majority of studies, doses of 200 mcg to 1,000 mcg of chromium picolinate were associated with improved glucose tolerance and lowered circulating insulin levels.11 In the past, some laboratory studies raised concerns about a potential risk for chromosomal abnormalities related to chromium,15 but no toxic effects have been reported in animal or human studies.16,17 The Institute of Medicine has concluded that chromium picolinate is safe when used as a dietary supplement.18
Cinnamon (Cinnamomum verum) is a traditional folk medicine used to treat diabetes in Korea, China and Russia.19 A study that evaluated the effects of 49 herbs, spices and medicinal plant extracts on insulin activity concluded that cinnamon had the most insulin-enhancing activity in rat fat cells tested in the laboratory. Activity was measured by the increase in carbon dioxide production after the addition of an extract; the more carbon dioxide produced by the fat cells, the greater the insulin-enhancing activity of the compound.20
Both animal and human studies have demonstrated lowered blood sugar and improved insulin resistance with cinnamon or cinnamon extracts. In a study of 60 men and women with type 2 diabetes, those treated with cinnamon (1, 2 or 5 g a day for 40 days) had decreases in fasting glucose levels of 18 percent to 29 percent.21 In a placebo-controlled, double-blind trial, 22 adults with pre-diabetes received a water-soluble cinnamon extract (500 mg a day) or placebo for 12 weeks. The researchers reported that 83 percent of those taking the extract experienced a significant decrease in fasting blood sugar, compared with 33 percent in the placebo group.22
Animal studies suggest that cinnamon extracts may improve the metabolic action of insulin and help prevent insulin resistance, in part by increasing glucose uptake into cells and enhancing the insulin-signaling pathway in muscle.23 One study in diabetic mice found that a cinnamon extract (200 mg per kilogram of body weight) caused significant decreases in blood sugar compared with the placebo group.19
The Food and Drug Administration concludes cinnamon is generally recognized as safe. However, it contains cinnamaldehyde, a constituent that is toxic in large doses. Water-soluble extracts are processed to filter out the toxins found in whole cinnamon while retaining the active components. No adverse effects have been reported for water-soluble cinnamon extracts.
Fenugreek (Trigonella foenum-graecum) has a long history of medicinal use in Ayurveda and Chinese medicine for diabetes, as well as for indigestion, elevated lipids and edema (fluid retention) of the legs. Preliminary animal and human trials suggest it has the potential to lower blood sugar levels.24 Several human trials of fenugreek in type 2 diabetes have demonstrated significant reductions in blood sugar, but most were short term, poorly controlled and involved small numbers of subjects.24,25 Preparations and doses of fenugreek used in the studies included 1 g per day of alcohol extract of fenugreek seed, 15 g a day of fenugreek seed powder in water, 25 g a day of powdered fenugreek seed and 100 g daily of fenugreek incorporated into bread.24,25
The herb's effects on blood sugar may be related to the ability of its compounds to increase tissue sensitivity to insulin,26 activate an insulin-signaling pathway in fat and liver cells,27 and delay emptying of the stomach.25 In diabetic rats, fenugreek leaf power (1 g per kilo?gram of body weight) was also found to reduce oxidative stress.28 No serious adverse effects have been reported in trials, though some diarrhea, dizziness and flatulence have been observed.24
Gymnema sylvestre is a woody climbing plant native to India, where it has been used for more than 2,000 years to treat "honey urine"—sugar that spills into the urine as a result of diabetes.29 There is little recent clinical evidence to support its use for treating diabetes, but a number of older trials yielded promising results. In one controlled study from 1990, 27 people with type 2 diabetes took 400 mg a day of a standardized gymnema extract for six to 30 months. Insulin requirements were decreased by about half and average blood-sugar levels decreased significantly as a result of treatment; there were no changes in the control group.30 In another study by the same investigators, 22 people with type 2 diabetes took 400 mg a day of gymnema extract for 18 to 20 months while continuing their prescribed hypoglycemic drugs. The researchers noted significant decreases in average blood sugar and an increase in the release of insulin from the pancreas. Subjects were able to decrease their doses of hypoglycemic medications; five people were able to discontinue drugs completely.31
Compounds in gymnema are believed to enhance glucose uptake into cells by increasing the permeability of cells.32 No significant adverse effects from gymnema have been reported.29
Magnesium The mineral magnesium is a co-factor for several enzymes required for carbohydrate metabolism. It is believed to play a role in blood-sugar control by helping to regulate insulin-mediated glucose uptake by cells.33 Several large prospective studies have identified a significant link between magnesium intake via food and supplements, lowered fasting insulin concentrations and a reduced incidence of type 2 diabetes, especially among overweight people.34,35,36,37 In African American and Hispanic populations, diabetics are reported to have lower serum magnesium levels than pre-diabetics or those with normal blood-sugar levels.38 Some suggest that a higher dietary intake of magnesium may protect against developing type 2 diabetes.39
An analysis of nine magnesium studies lasting four to 16 weeks at a median dose of 360 mg a day concluded that oral magnesium supplementation may effectively reduce fasting plasma glucose levels.40 The authors suggested that future studies should last at least four months and provide more than 360 mg a day of magnesium to demonstrate optimal blood-sugar control. The authors of another study suggested a similar threshold of at least 325 mg a day to improve insulin sensitivity.41 No serious adverse effects have been reported in association with magnesium. The most common side effects are mild abdominal pain, diarrhea and nausea.40
Supplements with promise
Of the six supplements reviewed here, chromium picolinate, cinnamon extract and magnesium appear to offer the most promise for reducing blood-sugar levels in people with pre-diabetes and type 2 diabetes, with the least potential for side effects. In the future, better-controlled studies could provide evidence that allow other supplements, such as bitter melon, fenugreek and gymnema, to live up to their traditional reputations, but for now, the findings are preliminary.
Densie Webb, Ph.D., R.D., is a freelance writer and industry consultant based in Austin, Texas.
1. American Diabetes Association. Diabetes Statistics. http://diabetes.org/diabetes-statistics.jsp
2. Torres W. Bitter Melon. www.charanteausa.com/ampalaya_archive/studies1.doc. Accessed March 21, 2007.
3. Leatherdale B, et al. Improvement in glucose tolerance due to Momordica charantia (karela). BMJ 282:1823-4, 1981.
4. Mahdi A, et al. Effect of herbal hypoglycemic agents on oxidative stress and antioxidant status in diabetic rats. IJCB 18(2):8-15, 2003.
5. Shetty A, et al. Effect of bitter gourd (Momordica charantia) on glycaemic status in streptozotocin induced diabetic rats. Plant Food Hum Nutr 60(3):109-12, 2005.
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7. Virdi J, et al. Antihyperglycemic effects of three extracts from Momordica charantia. J Ethnopharmacol 88(1):107-11, 2003.
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9. Dans A, et al. The effect of Momordica charantia capsule preparation on glycemic control in Type 2 Diabetes Melliutus needs further studies. J Clin Epidemol 2007;60:554-9.
10. Cefalu W, et al. Oral chromium picolinate improves carbohydrate and lipid metabolism and enhances skeletal muscle glut-4-translocation in obese, hyperinsulinemic (JCR-LA Corpulent) rats. J Nutr 132:1107-14, 2002.
11. Anderson R, et al. Supplemental chromium effects on glucose, insulin, glucagons, and urinary chromium losses in subjects consuming controlled low-chromium diets. Am J Clin Nutr 54:909-16, 1991.
12. Anderson R, et al. Elevated intakes of supplemental chromium improve glucose and insulin variables in individuals with type 2 diabetes. Diabetes 46(11):1786-91, 1997.
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14. Singer G, Geohas J. The effect of chromium picolinate and biotin supplementation on glycaemic control in poorly controlled patients with type-2 diabetes mellitus: a placebo-controlled, double-blinded, randomized trial. Diabetes Technol Ther 8(6):636-43, 2006.
15. Hepburn D, et al. Nutritional supplement chromium picolinate causes sterility and lethal mutations in Drosophila melanogaster. Proc Natl Acad Sci 100:3766-71, 2003.
16. Greenberg D, et al. Rat chromosomes are unharmed by orally administered chromium picolinate. J Am Coll Nutr 18:27, 1999.
17. Kato I, et al. Effect of supplementation with chromium picolinate on antibody titers to5-hydroxymethyl uracil. Eur J Epidemiol 14:621-6, 1998.
18. Berner T, et al. Determining the safety of chromium tripicolinate for addition to foods as a nutrient supplement. Food Chem Toxicol 42:1029-42, 2004.
19. Kim S, et al. Anti-diabetic effect of cinnamon extract on blood glucose in db/db mice. J Ethnopharmacol 104:119-23, 2006.
20. Broadhurst C, et al. Insulin-like biological activity of culinary and medicinal plant aqueous extracts in vitro. J Agric Food Chem 48:849-52, 2000.
21. Khan A, et al. Cinnamon improves glucose and lipids of people with type 2 diabetes. Diabetes Care 26(12):3215-8, 2003.
22. Ziegenfuss T, et al.?Effects of a water-soluble cinnamon extract on body composition and features of the metabolic syndrome in pre-diabetic men and women. JISSN 3(2):45?53, 2006.
23. Qin B, et al. Cinnamon extract (traditional herb) potentiates in vivo insulin-regulated glucose utilization via enhancing insulin signaling in rats. Diabetes Res Clin Prac 62:139-48, 2003.
24. Basch E, et al. Therapeutic applications of fenugreek. Alt Med Rev 8(1):20-7, 2003.
25. Yeh G, et al. Systematic review of herbs and dietary supplements for glycemic control in diabetes. Diabetes Care 26(4):1277-94, 2003.
26. Puri D, et al. Mechanism of action of a hypoglycemic principle isolated from fenugreek seeds. Indian J Physiol Pharmacol 46(4):457-62, 2002.
27. Vijayakumar M, et al. The hypoglycemic activity of fenugreek seed extract is mediated through the stimulation of an insulin signaling pathway. Br J Pharmacol 146(1):41-8, 2005.
28. Annida B, Prince P. Supplementation of fenugreek leaves reduces oxidative stress in streptozotocin-induced diabetic rats. J Med Food 8(3):382-5, 2005.
29. Monograph Gymnema sylvestre. Alt Med Rev 4(1):46-7, 1999.
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32. Persaud S, et al. Gymnema sylvestre stimulated insulin release in vitro by increased membrane permeability. J Endocrin 163:207-12, 1999.
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34. Fung T, et al. The association between magnesium intake and fasting insulin concentration in healthy middle-aged women. J Am Coll Nutr 22(6):533-8, 2003.
35. Song Y, et al. Dietary magnesium intake in relation to plasma insulin levels and risk of type 2 diabetes in women. Diabetes Care 27(1):59-65, 2004.
36. Lopez-Ridaura R, et al. Magnesium intake and risk of type 2 diabetes in men and women. Diabetes Care 27(1):134-40, 2004.
37. van Dam R, et al. Dietary calcium and magnesium, major food sources, and risk of type 2 diabetes in U.S. black women. Diabetes Care 29:2238-43, 2006.
38. Chambers E, et al. Serum magnesium and type 2 diabetes in African Americans and Hispanics: a New York cohort. J Am Coll Nutr 25(6):509-13, 2006.
39. Rumawas M, et al. Magnesium intake is related to improved insulin homeostasis in the Framingham offspring cohort. J Am Coll Nutr 25(6):486-92, 2006.
40. Song Y, et al. Effects of oral magnesium supplementation on glycaemic control in type 2 diabetes: a meta-analysis of randomized double-blind controlled trials. Diabet Med 23:1050-6, 2006.
41. Ma B, et al. Dairy, magnesium, and calcium intake in relation to insulin sensitivity: approaches to modeling a dose-dependent association. Am J Epidemiol 164(5):449-59, 2006.
Natural Foods Merchandiser volume XXVIII/number 7/p.36-39