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.
In an attempt to replicate these results, a group of Dutch researchers performed a carefully designed 6-week double-blind, placebo-controlled study of 25 people with diabetes. 20 All participants were given 1.5 g of cinnamon daily. The results failed to show any detectable effect on blood sugar, insulin sensitivity, or cholesterol profile. Although this second study was smaller than the first because it had fewer groups, overall, its statistical validity is similar. These unsupportive results were confirmed in a Thai study enrolling 60 people: 1.5 g of cinnamon daily failed to produce any benefit. 24 On the other hand, a double-blind study of 79 people that used 3 g instead of 1.5 g daily did find that cinnamon improved blood sugar levels. 21 And, a randomized trial involving 58 people with type 2 diabetes also concluded that 2 g of cinnamon daily reduced HbA1c levels (a measurement of blood sugar levels over time), as well as high blood pressure. 27
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 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.
5. Quale JM, Landman D, Zaman MM, et al. In vitro activity of Cinnamomum zeylanicum against azole resistant and sensitive Candida species and a pilot study of cinnamon for oral candidiasis. Am J Chin Med. 1996;24:103-109.
8. Oishi K, Mori K, Nishiura Y. Food hygienic studies on Anisakinae larvae. Effects of some spice essential oils and food preservatives on mortality of Anisakinae larvae. Bull Jap Soc Sci Fish. 1974;40:1241-1250.
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.
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.
28. Lungarini S, Aureli F, Coni E. Coumarin and cinnamaldehyde in cinnamon marketed in Italy: a natural chemical hazard? Part A, Chemistry, Analysis, Control, Exposure & Risk Assessment. Food Additives & Contaminants. 2008;25(11):1297-1305.
Last reviewed August 2013 by EBSCO CAM Review Board
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