Cinnamomum zeylanicum, Cinnamon cassia
Most Americans consider cinnamon a simple flavoring, but in traditional Chinese medicine, it's one of the oldest remedies, prescribed for everything from diarrhea and chills to influenza and parasitic worms. Cinnamon comes from the bark of a small Southeast Asian evergreen tree and is available as an oil, extract, or dried powder. It's closely related to cassia ( C. cassia) and contains many of the same components, but the bark and oils from C. zeyleanicum are thought to have a better flavor.
Based on the results of one preliminary double-blind, placebo-controlled study, cinnamon has been widely advertised as an effective treatment for type 2 diabetes as well as high cholesterol. However, the evidence for this is mixed.
Preliminary results from test tube and animal studies suggest that cinnamon oil and cinnamon extract have antifungal, antibacterial, and antiparasitic properties.4-10 For example, cinnamon has been found to be active against Candida albicans, the fungus responsible for vaginal yeast infections and thrush (oral yeast infection), Helicobacter pylori (the bacteria that causes stomach ulcers), and even head lice. However, it's a long way from studies of this type to actual proof of effectiveness. Until cinnamon is tested in double-blind human trials, we can't conclude that it can successfully treat these or any other infections. (For why double-blind studies are so important, see Why Does This Database Rely on Double-blind Studies?)
Based on previous animal studies that had suggested potential benefits of cinnamon for diabetes,11,12 researchers in Pakistan performed a double-blind, placebo-controlled trial.19 In this 40-day study, 60 people with type 2 diabetes were given cinnamon at a dose of 1, 3, or 6 g daily. The results reportedly indicated that use of cinnamon improved blood sugar levels by 18%-29%, total cholesterol by 12%-26%, LDL (“bad”) cholesterol by 7%-27%, and triglycerides by 23%-30%. These results were said to be statistically significant as compared to the beginning of the study and to the placebo group.
However, this study has some odd features. The most important is that it found no significant difference in benefit between the various doses of cinnamon. This is called lack of a dose-related effect, and it generally casts doubt on the results of a study. The researchers counter that perhaps even 1 g of cinnamon is sufficient to produce the maximum cholesterol-lowering effect, and therefore, higher doses simply didn’t add any further benefit. There is another problem with this study as well: no improvements were seen in the placebo group. This too is unusual, and also casts doubt on the results.
Seven randomized trials that examined the benefits of 1-2 g of cinnamon daily for blood glucose or HbA1c control found conflicting results. Two trials found that daily cinnamon over 3 months was associated with a greater reduction in HbA1c (0.83% change in 1 trial) compared to placebo.27, 31 Two trials found daily cinnamon helped reduce blood glucose, though one of those trials found no benefit in HbA1c measures.19, 21 However, two trials found no benefits for HbA1c or blood glucose with daily cinnamon23, 25 and an additional trial found no blood glucose benefits alone.20 Cinnamon also had inconsistent blood pressure outcomes with one trial finding a reduction in systolic and diastolic pressure in people with diabetes27 but a second trial finding no change in systolic pressure.32
In yet another small study involving 22 prediabetic patients with metabolic syndrome, researchers found that an extract containing 500 mg cinnamon given once daily was effective at modestly reducing fasting blood sugar and systolic blood pressure, and increasing lean body weight. However, the low dosage of cinnamon used in this study raises concerns about the reliability of these results.26 And, a very small study that evaluated cinnamon for improving blood sugar control in women with polycystic ovary disease found evidence of benefit.22
Regarding type 1 diabetes, a study of 72 adolescents failed to find benefit with cinnamon taken at a dose of 1 g daily.23
Systematic reviews can sometimes clarify the existence of benefits but two systematic reviews published in 2012 and 2013 only provided conflicting results. The first review included a meta-analysis of 10 randomized trials with 577 patients who were given an average dose of 2 g of cinnamon per day for 4-16 weeks. The use of cinnamon was not associated with differences in blood glucose, HbA1c, or insulin levels when compared to placebo or usual care. However, most trials in this review had a moderate or high risk of bias, which affect the reliability of the results.30
The second review included 10 randomized trials with 543 patients who were given doses of cinnamon ranging from 0.12 g to 6 g. Those taking cinnamon showed significant decreases in blood glucose, cholesterol, and triglyceride levels when compared to placebo or no treatment. Although, there was no difference in HbA1c levels between the groups. Unfortunately, the wide variety of doses and length of treatment used in the included trials makes it impossible to determine an ideal dosage for treatment.29
The bottom line: The evidence regarding cinnamon as a treatment for diabetes or high cholesterol with diabetes is highly inconsistent, suggesting that if cinnamon is indeed effective, the dosage is very unclear and its benefits may be minimal at most.
Typical recommended dosages of ground cinnamon bark are 1 to 4 g daily. Cinnamon oil is generally used at a dose of 0.05 to 0.2 g daily.13
As a widely used food spice, ground cinnamon bark is believed to be safe. However, little is known about the maximum safe dosage of cinnamon found in capsules and in essential oil. Confusing the picture is the fact that Ceylon cinnamon (sometimes referred to as "true cinnamon") is different than the cassia variety. Only the latter contains significant amounts of coumarin, which has been shown to cause liver and kidney damage at high doses in rats and other animals.28 Although there is limited evidence of such harm occurring in humans, it would be prudent for people with known liver or kidney disease to avoid dietary supplements containing cassia cinnamon. There is some evidence that high doses of cinnamon oil might depress the central nervous system.14 Germany's Commission E recommends that pregnant women should avoid taking cinnamon oil or high doses of the bark.15
When used topically, cinnamon bark oil may cause flushing and a burning sensation.16 Some people have reported strong burning sensations or mouth ulcers after chewing cinnamon-flavored gum or candy.17,18 However, these reactions disappeared within days of discontinuing the gum.
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10. Quale JM, Landman D, Zaman MM, et al. In vitro activity of Cinnamomumzeylanicum against azole resistant and sensitive Candida species and a pilot study of cinnamon for oral candidiasis. Am J Chin Med. 1996;24:103-109.
11. Imparl-Radosevich J, Deas S, Polansky MM, et al. Regulation of PTP-1 and insulin receptor kinase by fractions from cinnamon: implications for cinnamon regulation of insulin signalling. Horm Res. 1998;50:177-182.
12. Onderoglu S, Sozer S, Erbil KM, et al. The evaluation of long-term effects of cinnamon bark and olive leaf on toxicity induced by streptozotocin administration to rats. J Pharm Pharmacol. 1999;51:1305-1312.
13. Leung AY, Foster S. Encyclopedia of Common Natural Ingredients Used in Food, Drugs, and Cosmetics. 2nd ed. New York, NY: Wiley; 1996: 168.
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16. Perry PA, Dean BS, Krenzelok EP. Cinnamon oil abuse by adolescents. Vet Hum Toxicol. 1990;32:162-164.
17. Allen CM, Blozis GG. Oral mucosal reactions to cinnamon-flavored chewing gum. J Am Dent Assoc. 1988;116:664-667.
18. Mihail RC. Oral leukoplakia caused by cinnamon food allergy. J Otolaryngol. 1992;21:366-367.
19. Khan A, Safdar M, Ali Khan MM, et al. Cinnamon improves glucose and lipids of people with Type 2 diabetes. Diabetes Care. 2003;26:3215-3218.
20. Vanschoonbeek K, Thomassen BJ, Senden JM, et al. Cinnamon supplementation does not improve glycemic control in postmenopausal type 2 diabetes patients. J Nutr. 2006;136:977-980.
21. Mang B, Wolters M, Schmitt B, et al. Effects of a cinnamon extract on plasma glucose, HbA, and serum lipids in diabetes mellitus type 2. Eur J Clin Invest. 2006;36:340-344.
22. Wang JG, Anderson RA, Chu MC, et al. The effect of cinnamon extract on insulin resistance parameters in polycystic ovary syndrome: a pilot study. Fertil Steril. 2007 Feb 9. [Epub ahead of print]
23. Altschuler JA, Casella SJ, Mackenzie TA, et al. The effect of cinnamon on A1C among adolescents with type 1 diabetes. Diabetes Care. 2007;30:813-816.
24. Suppapitiporn S, Kanpaksi N, Suppapitiporn S. The effect of cinnamon cassia powder in type 2 diabetes mellitus. J Med Assoc Thai. 2006;89(suppl 3):S200-S205.
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26. Ziegenfuss TN, Hofheins JE, Mendel RW, et al. Effects of a water-soluble cinnamon extract on body composition and features of the metabolic syndrome in pre-diabetic men and women. J Int Soc Sports Nutr. 2006;3:45-53.
27. Akilen R, Tsiami A, Devendra D, Robinson N. Glycated haemoglobin and blood pressure-lowering effect of cinnamon in multi-ethnic Type 2 diabetic patients in the UK: a randomized, placebo-controlled, double-blind clinical trial. Diabet Med. 2010;27(10):1159-1167.
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29. Allen RW, Schwartzman E, et al. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis. Ann Fam Med. 2013;11(5):452-459.
30. Leach MJ, Kumar S. Cinnamon for diabetes mellitus. Cochrane Database Syst Rev. 2012;9:CD007170.
31. Crawford P. Effectiveness of cinnamon for lowering hemoglobin A1C in patients with type 2 diabetes: a randomized, controlled trial. J Am Board Fam Med. 2009 Sep-Oct;22(5):507-12.
32. Wainstein J, Stern N, Heller S, Boaz M. Dietary cinnamon supplementation and changes in systolic blood pressure in subjects with type 2 diabetes. J Med Food. 2011 Dec;14(12):1505-10
Last reviewed December 2015 by EBSCO CAM Review Board
Last Updated: 12/15/2015
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