Posted: 12/26/2015 Last Update: 11/5/16
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- Cinnamon may modestly help control blood sugar levels (See What It Does). The active compounds are believed to be proanthocyanidins (PACs). In the supplements CL tested, we found that PACs ranged from less than 1 mg to more than 100 mg per daily serving. Some cinnamon extracts contained surprisingly small amounts of PACs (See comparisons in the 4th column, Supplements Results Table).
- A dose of 1 gram (1/2 teaspoon) of cinnamon bark powder per day may be sufficient to cause a blood sugar-lowering effect in people with type 2 diabetes or prediabetes. With some extracts, smaller doses may be sufficient. (See What to Consider When Using).
- A concern with cinnamon is that some species contain significant amounts of coumarin -- a naturally-occurring compound which may cause liver toxicity and is a potential carcinogen. Although none of the products exceeded the tolerable daily intake limit (TDI) for an average-sized adult, several should only be used with caution in children (See 5th column, Supplements Results Table). None of the supplements exceeded contamination limits for heavy metals or Salmonella.
- For best choices, see What CL Found, Supplements.
- All 3 spices passed testing for filth, Salmonella, and heavy metals.
- If you use cinnamon spice routinely, be aware that some contain significant amounts of coumarin. Those made from Ceylon cinnamon contain extremely little, but, products made with Cinnamomum cassia tend to contain moderate amounts, and those with Cinnamomum lorreirii can have particularly high amounts. (See 3rd column, Spices Results Table)
- For best choices, see What CL Found, Spices.
What It Is:
Cinnamon is a spice commonly used for fragrance and food flavoring. Traditionally, it has been used to treat a wide range of ailments, from digestive complaints to parasitic infections.
There two main varieties of cinnamon found in cooking spices and supplements: The most commonly sold in the U.S., is cassia cinnamon (species names include Cinnamomum cassia or aromaticum [Chinese], Cinnamomum burmannii [Indonesian], Cinnamomum loureirii [Saigon or Vietnamese — also spelled loureiroi]; the most expensive and less common variety is Ceylon cinnamon (Cinnamomum verum or Cinnamomum zeylanicum), also referred to as "True Cinnamon." Supplements typically contain cassia cinnamon although some, often labeled as "True Cinnamon," do contain the Ceylon variety.
Unlike Ceylon, cassia cinnamon contains relatively high levels of a naturally-occurring, but toxic substance called coumarin. Nevertheless, cassia cinnamon is generally recognized as safe (GRAS) by the U.S. FDA — although there is concern that chronic, high doses could potentially have adverse effects (See the Concerns and Cautions for more information).
Cinnamon contains a type of polyphenol called proanthocyanidins (PACs), which are linked flavanols thought to be responsible for some of its beneficial effects (Anderson, J. Agric. Food Chem. 2004). PACs are characterized by their "degree of polymerization" or "linkages," (i.e. DP-1, DP-2, DP-3 etc.), and, in this Review, we've tested and reported the amounts of DP-1 through DP-7 found in various cinnamon supplements, listed in the fourth column of the results table as "Proanthocyanidins (PACs) per Daily Serving."
What It Does:
The majority of research on the health benefits cinnamon focuses on cassia cinnamon.
Blood sugar and type 2 diabetes and pre-diabetes
Type 2 diabetes:
Some, but not all studies, have found cinnamon may modestly improve blood sugar in people with type 2 diabetes whose blood sugar is not well controlled with medication. For example, a small study in Pakistan among men and women with type 2 diabetes (average age 52) who were taking sulfonylurea drugs (i.e. glibenclamide) found that those who took either 1 gram, 3 grams, or 6 grams of ground cassia cinnamon (in capsules taken in divided doses after meals) daily for a little over one month had similar, significant reductions in fasting glucose (between 18 to 29%), triglycerides (23-30%) , LDL cholesterol (7-27%) and total cholesterol (12-26%) while there we no such changes in those who took a placebo (Khan, Diabetes Care 2003).
A study among men and women age 48 or older with type 2 diabetes who were taking an oral hypoglycemic drug (30 mg of gliclazide (Diamicron) per day) found that a dose of either 120 mg or 360 mg of cassia cinnamon extract (each 120 mg was extracted, using water, from 4,800 mg of cinnamon — a 40:1 extract made by Shanghai Yitian Bio-Scientific Co, Ltd, China) taken before breakfast every day for three months significantly reduced fasting blood sugar and HbA1c (a measure of blood sugar over several months) compared to placebo (Lu, Nutr Res 2012). Those who took the lower dose of cinnamon extract had an average reduction in fasting blood sugar of 1.01 mmol/L (from 9.00 to 7.99 mmol/L) and an average 0.67% reduction in HbA1c (from 8.9% to 8.23%) while those in the higher dose group had an average fasting blood sugar reduction of 1.62 mmol/L (from 11.21 to 9.59 mmol/L) and an average 0.92% reduction in HbA1c (from 8.92% to 8.00%). Interestingly, triglyceride levels were significantly decreased but only in those who took the lower dose of cinnamon extract; there were no changes in total cholesterol, "good" HDL cholesterol or "bad" LDL cholesterol.
Another study among adults with type 2 diabetes taking oral hypoglycemic medication but who had an HbA1c above 7% found that capsules containing 500 mg of cassia cinnamon powder (Holland and Barrett Ltd, UK) taken with meals (one capsule with breakfast, two capsules with lunch and one capsule with dinner — a total daily dose of 2 grams of cinnamon powder per day) for three months significantly reduced HbA1c from an average of 8.22% to 7.86%, while there was a slight increase in average HbA1c in the placebo group (Akilen, Diabet Med 2010). Fasting blood sugar was not significantly reduced compared to placebo; however, this may be due to the fact that the placebo used (starch powder) is known to lower fasting blood glucose. There was also small but significant decrease in systolic and diastolic blood pressure among those who took the cinnamon powder, compared to placebo. (Another study in people with type 2 diabetes who took 1,200 mg of cinnamon per day for 3 months found no significant decrease in blood pressure (Wainstein, J Med Food 2011).
A 3-month study involved giving cinnamon to men and women (average age 60) with poorly-controlled type 2 diabetes, and the effects were judged according to improvements in levels of HbA1c, a form of hemoglobin. The percentage of total hemoglobin which is HbA1c indicates how well diabetes has been controlled in recent weeks; ideally it should be below 6 or 7%. Those who took two 500 mg capsules of cassia cinnamon (a total daily dose of 1 gram) with food in addition to their standard care had a decrease in HbA1c from 8.47% to 7.63%, which was somewhat greater than the decrease found among those who received only standard care and experienced a decrease from 8.28% to 7. 91%. (Crawford, J Am Board Fam Med 2009).
However, other studies have reported no benefit for people with type 2 diabetes. For example, a small study in postmenopausal women with type 2 diabetes who were either taking oral blood sugar-lowering medication or were trying to control blood sugar through diet found that a capsule containing 500 mg of cassia cinnamon taken with breakfast, lunch and dinner (a total daily dose of 1.5 g/day) for 6 weeks did not improve oral glucose tolerance or measures of whole-body insulin sensitivity (Vanschoonbeek, J Nutr 2006). Another study among adults with type 2 diabetes found that taking a capsule containing 500 mg of cassia cinnamon with breakfast and again with dinner for 40 days had no effect on body mass index, HbA1c, triglyceride, cholesterol or insulin levels compared to placebo. (Blevins, Diabetes Care 2007).
Interestingly, a study using cassia cinnamon significantly reduced blood sugar response when taken with glucose during an oral glucose tolerance test (OGTT), but a study using a similar amount of Ceylon cinnamon found no effect on blood sugar levels (Solomon, Diabetes Obes Metab 2007; Wickenberg, Br J Nutr 2012).
In an analysis of 10 clinical trials investigating the use of cinnamon (either a liquid extract or raw powder of cassia cinnamon, although two studies did not specify), the researchers concluded that a dose between 120 mg extract and 6 grams of bark powder per day "may have a beneficial effect on fasting plasma glucose, LDL-C, HDL-C, and triglyceride levels in patients with type 2 diabetes," but found no "statistically significant effect on HbA1c" (Allen, Ann Fam Med 2013).
Studies using cinnamon extracts suggest modest reductions in blood sugar among adults with prediabetes, but more rigorous studies are needed.
A small study in prediabetic men and women with metabolic syndrome found that those who took a capsule containing 250 mg of a water soluble extract (20:1) of cassia cinnamon standardized to 1% doubly-linked type-A PACs (Cinnulin PF -- the type in CinnaBetic II in this Review) with breakfast and with dinner (a total daily dose of 500 mg of extract) for 3 months had significant decreases in fasting blood sugar (an average decrease of about 10 mg/dL) and systolic blood pressure (an average decrease of about 5 mm Hg), and an increase in lean mass (an average of about 1 kg) compared to those who took a placebo (Ziegenfuss, J Int Soc Sports Nutr 2006). A study comparing the effects of Cinnulin PF with an oral medication to reduce blood sugar (Metformin) and cinnamon bark is currently underway (ClinicalTrials.gov 2015). ConsumerLab.com will report on the results when they become available.
A study in China among adults with elevated blood sugar levels found that 250 mg twice a day of a water extract of cinnamon (CinSulin) modestly reduced average fasting glucose levels from 8.85 mmol/L to 8.19 mmol/L. However, the researchers failed to determine if this was statistically significant relative to effects seen in those given placebo (baked wheat flour), whose levels also fell -- from 8.57 mmol/L to 8.44 mmol/L. 2-hr glucose and HOMA-IR values also decreased modestly in the cinnamon group but, again, it was not noted if this was significant relative to placebo. (Note: The CinSulin supplement tested by ConsumerLab.com for this Review may be similar to that in the study but includes chromium and vitamin D) (Anderson, J Trad Compl Med 2016).
Cinnamon contains a compound called cinnamaldehyde which may have anti-microbial activity; there is very preliminary evidence that both cassia and Ceylon cinnamon may inhibit the growth of certain microbes (Nuryastuti, Appl Environ Microbiol 2009; Muthuswamy, J Food Safety 2008); for example, the use of cinnamon gum and candies have been reported to improve oral candidiasis (oral thrush) in several people with HIV (Quale Am J Chin Med 1996).
Laboratory and animal studies suggest cinnamon has antioxidant and anti-inflammatory activity (Kawatra, Pharmacognosy Res 2015); PACs from cinnamon may help to inhibit the formation of advanced glycation endproducts (AGEs), which are thought to play a role in conditions such as diabetes, atherosclerosis and Alzheimer's disease (Peng, J Agric Food Chem 2010). A particular liquid extract of Ceylon cinnamon has been found to reduce markers of oxidative stress and improve certain measures of cognitive function in rats (Jain, Nutr Neurosci 2015; Malik, J Basis Clin Physiol Pharmacol 2015). However, there do not appear to be any studies on the use of cinnamon in people to improve cognitive function.
For more information see the Encyclopedia article about Cinnamon.
Quality Concerns and What CL Tested for:
Like other supplements, neither the FDA nor any other federal or state agency routinely tests cinnamon supplements for quality prior to sale. However, quality issues for cinnamon supplements can include the following:
ConsumerLab.com, as part of its mission to independently evaluate products that affect health, wellness, and nutrition, purchased cinnamon supplements sold in the U.S. and tested them to determine 1) the amount of PACs in a daily suggested serving, 2) if they exceeded unacceptable levels of lead, cadmium, or arsenic or were contaminated with Salmonella, 3) if they exceeded the tolerable intake level of coumarin for an adult, also noting if the limit for a 35 kg (77 lb) child would be exceeded, and 4) for those sold as regular tablets, if they could disintegrate properly in order to release their contents for absorption (see Testing Methods and Passing Score).
- PACs: Is it real and does it contain key compounds? As discussed above (What It Is), PACs are compounds expected in cinnamon and may be responsible for its glucose lowering effects.
- Purity: Does the product contain contaminants? Like other supplements made from plants, cinnamon may be contaminated with heavy metals, such as lead, cadmium, and arsenic. In children, infants, and fetuses, even low levels of lead can adversely affect neurobehavioral development and cognitive function. In adults, lead at somewhat higher levels can cause elevated blood pressure, anemia, and adversely affect the nervous and reproductive systems. Lead is of particular concern during pregnancy as the mother can transfer it to the fetus. Cadmium is a carcinogen and kidney toxin. Arsenic is a carcinogen and can damage organs. Potential contamination with Salmonella is also a concern with spices.
- Coumarin: Is it safe? Cassia cinnamon may naturally contain a significant concentration of coumarin, which has been shown in animal studies to be toxic to the liver and a potential carcinogen. A tolerable daily intake (TDI) of coumarin of 0.1 mg per kilogram of body weight (e.g., 7 mg for a 70 kg or 154 lb adult) has been established by the European Food Safety Authority. This is based on daily consumption over long periods of time. Exposure to an intake three times higher than the TDI for one to two weeks is not a safety concern.
- Ability to Break Apart Properly Once in your body, will the pill break down properly (disintegrate) so that it can release its contents?
ConsumerLab.com also purchased several bottles of ground cinnamon bark spice, as used in cooking, and tested each for Salmonella and filth, as well as for lead, cadmium, and arsenic. The spices were also tested for amounts of coumarin.