Cinnamon

What it is

Cinnamon is the dried bark of trees in the genus Cinnamomum, sold both as a culinary spice and as a concentrated supplement. Two commercially distinct types dominate: cassia cinnamon and Ceylon or 'true' cinnamon, which differ in chemical composition. The difference matters because the natural compound coumarin is present at up to about 1% in cassia bark but only in trace amounts in Ceylon. Supplement and spice labels frequently do not state which species or plant part was used.

What the research says

The evidence is disputed rather than settled. Pooled analyses of randomised trials in type 2 diabetes and PCOS report small reductions in fasting glucose and HbA1c, but the Cochrane review of the same field found no statistically significant difference in HbA1c, insulin or post-meal glucose and concluded the evidence was insufficient, with most trials at high or unclear risk of bias. No trial has reported whether cinnamon changes diabetes complications, quality of life or mortality. The clearest, most reproducible signal attached to cinnamon is not a benefit but a hazard: the coumarin content of cassia bark, which is liver-toxic in animals and has a European tolerable daily intake of 0.1 mg/kg body weight.

Evidence grade: Disputed.

What goes wrong

Cassia cinnamon bark contains coumarin at up to about 1% by weight while Ceylon cinnamon contains only trace amounts, and on the German retail market the botanical species is often not stated on the packaging. (Source 1)

• Expert review, not systematic, Certainty not rated.
• Size: not applicable - analytical review of published coumarin determinations.
• Who: retail cinnamon spice samples, Europe and USA.
• How long: not applicable.
• Result: coumarin up to 1% in cassia versus about 0.004% in Ceylon cinnamon.
• Funding: not stated.

In comparison, in Cassia cinnamon, coumarin content is up to 1%, whereas in Ceylon cinnamon is very low (trace), about 0.004%.

EFSA's flavourings panel derived a tolerable daily intake for coumarin of 0-0.1 mg/kg body weight based on liver toxicity in a two-year dog study, a value the German BfR later reached independently from human medicinal data. (Source 2)

• Official position, Certainty not rated.
• Size: not applicable - regulatory toxicological evaluation.
• Who: general population exposed to coumarin in food.
• How long: lifetime daily intake.
• Result: TDI 0 - 0.1 mg coumarin/kg body weight, set by EFSA in 2004 and reconfirmed by BfR.
• Funding: government agency evaluation.

Established TDI, based on hepatotoxicity in a two-year dog study, was 0 - 0.1 mg coumarin/kg bw.

A published case report describes acute hepatitis in a 73-year-old woman who began cinnamon supplements while taking a statin, with liver injury resolving after both were stopped and the statin alone later tolerated. (Source 3)

• Case report, Very low certainty.
• Size: 1 patient.
• Who: 73-year-old woman on long-term statin therapy for coronary artery disease.
• How long: symptoms after about 1 week of cinnamon supplementation.
• Result: hepatitis confirmed on laboratory workup and imaging; no other cause found; statin rechallenge without cinnamon was uneventful.
• Funding: not stated.

A 73-year-old woman was seen in the Emergency Department complaining of abdominal pain associated with vomiting and diarrhea after she started taking cinnamon supplements for about 1 week.

Adulterated cinnamon used in apple cinnamon fruit puree pouches was linked to roughly 500 cases of childhood lead exposure across the United States, first detected through four North Carolina children with elevated blood lead levels. (Source 4)

• Case series, Certainty not rated.
• Size: 4 index children in North Carolina; approximately 500 cases nationwide.
• Who: young children consuming apple cinnamon fruit puree pouches.
• How long: June 2023 to January 2024.
• Result: blood lead levels at or above 5 micrograms per decilitre in the index children; approximately 500 cases nationally; product voluntarily recalled.
• Funding: government public health investigation.

A collaborative multilevel response led to detection of approximately 500 cases of childhood lead exposure potentially linked to consumption of apple cinnamon purees nationwide.

NCCIH's position, last updated November 2024, is that prolonged use of cassia cinnamon could be an issue for sensitive people such as those with liver disease, while also stating that consuming cassia cinnamon does not usually supply enough coumarin to cause significant problems although some cassia products contain high levels of it. (Source 5)

• Official position, Certainty not rated.
• Size: not applicable - agency summary.
• Who: general public using cinnamon as food or supplement.
• How long: not applicable.
• Result: no quantified effect; qualitative safety position: coumarin-liver interactions reported, ordinary cassia consumption not usually enough coumarin to cause significant problems, some cassia products high in coumarin, prolonged cassia use an issue for sensitive people such as those with liver disease, and Ceylon cinnamon containing only a trace amount of coumarin.
• Funding: US government agency.

Consuming cassia cinnamon doesn't usually include enough coumarin to cause significant problems; however, some cassia cinnamon products contain high levels of coumarin. Prolonged use of cassia cinnamon could be an issue for sensitive people, such as those with liver disease.

What the evidence supports

An umbrella meta-analysis of 11 meta-analyses of randomised trials found small pooled reductions in fasting glucose, insulin, HOMA-IR and HbA1c with cinnamon supplementation in type 2 diabetes or PCOS. (Source 6)

• Review of reviews, Certainty not rated.
• Size: 11 meta-analyses of randomised controlled trials.
• Who: patients with type 2 diabetes or polycystic ovary syndrome.
• How long: not stated in the pooled abstract.
• Result: FPG WMD -10.93 mg/dL (95%CI -16.22, -5.65); insulin WMD -2.01 IU/mL (95%CI -3.96, -0.07); HOMA-IR WMD -0.61 (95%CI -0.91, -0.31); HbA1c WMD -0.10% (95%CI -0.17, -0.03)
• Funding: not stated.

Cinnamon supplementation was effective in reducing serum FPG (WMD: -10.93 mg/dL; 95%CI: -16.22, -5.65; SMD: -0.86; 95%CI: -1.19, -0.52)

What the evidence does not support

The Cochrane review of cinnamon in diabetes found no statistically significant difference from control in HbA1c, serum insulin or postprandial glucose. (Source 7)

• Systematic review, Low certainty.
• Size: 10 randomised controlled trials, 577 participants.
• Who: adults and children with type 1 and type 2 diabetes mellitus.
• How long: 4 to 16 weeks.
• Result: no statistically significant difference in HbA1c, serum insulin or postprandial glucose; effect on fasting blood glucose described as inconclusive.
• Funding: not stated.

No statistically significant difference in glycosylated haemoglobin A1c (HbA1c), serum insulin or postprandial glucose was found between cinnamon and control groups.

The same Cochrane review rated the trial evidence as largely poor quality, with risk of bias high or unclear in all but two trials. (Source 7)

• Systematic review, Low certainty.
• Size: 10 randomised controlled trials, 577 participants.
• Who: people with type 1 and type 2 diabetes mellitus.
• How long: 4 to 16 weeks.
• Result: risk of bias high or unclear in 8 of 10 trials; high in some domains in 50% of trials.
• Funding: not stated.

Risk of bias was high or unclear in all but two trials, which were assessed as having moderate risk of bias.

No cinnamon trial in the Cochrane review reported quality of life, diabetes complications, morbidity, mortality or costs, so nothing is known about outcomes that matter to patients. (Source 7)

• Systematic review, Low certainty.
• Size: 10 randomised controlled trials, 577 participants.
• Who: people with type 1 and type 2 diabetes mellitus.
• How long: 4 to 16 weeks.
• Result: no data reported for any patient-important endpoint.
• Funding: not stated.

No trials reported health-related quality of life, morbidity, mortality or costs.

Cochrane's authors concluded there is insufficient evidence to support cinnamon use in type 1 or type 2 diabetes. (Source 8)

• Systematic review, Low certainty.
• Size: 10 randomised controlled trials, 577 participants.
• Who: people with type 1 and type 2 diabetes mellitus.
• How long: 4 to 16 weeks.
• Result: no reliable benefit demonstrated.
• Funding: not stated.

There is insufficient evidence to support the use of cinnamon for type 1 or type 2 diabetes mellitus.

Where the evidence is mixed

In a retrospective clinical series of 129 Japanese outpatients on cinnamon-bark-containing Kampo medicines, 76% exceeded the European coumarin tolerable daily intake yet abnormal liver function tests were no more common in that group. (Source 9)

• Cohort study, Very low certainty.
• Size: 129 outpatients (18 male, 111 female, median age 58 years)
• Who: Japanese outpatients prescribed keishibukuryogankayokuinin (TJ-125) between April 2008 and March 2013.
• How long: prescriptions over a five-year period, retrospectively reviewed.
• Result: median coumarin intake 0.113 mg/kg/day; 98/129 (76.0%) above the TDI; abnormal liver function tests in 6/31 (19.4%) below TDI versus 17/98 (17.3%) at or above TDI.
• Funding: not stated.

Twenty-three patients had an abnormal change in liver function test value, but no significant difference was found in the incidence of abnormal change between the group consuming less than the TDI value (6/31, 19.4%) and the group consuming equal to or greater than the TDI value (17/98, 17.3%).

An umbrella review of the safety literature found no significant excess of toxic or side effects with cinnamon versus placebo, but rated the underlying reviews only low to moderate quality. (Source 10)

• Review of reviews, Low certainty.
• Size: 3 meta-analyses and 1 systematic review.
• Who: participants in randomised controlled trials of oral cinnamon.
• How long: varied across included reviews.
• Result: no significant difference in toxic or side effects between cinnamon and placebo regardless of dose and duration; review quality low in 2 of 4 and moderate in 2 of 4.
• Funding: not stated.

There were no significant toxic- or side effects between cinnamon group and placebo group regardless of dose and duration.

Most of the mechanistic support for cinnamon's antidiabetic and other activities comes from laboratory and animal work rather than human outcome trials. (Source 11)

• Expert review, not systematic, Certainty not rated.
• Size: not applicable - comprehensive review of the genus.
• Who: in vitro systems and animal models, plus some clinical studies.
• How long: not applicable.
• Result: no pooled human effect estimate; mechanisms described from preclinical studies.
• Funding: not stated.

The preclinical (in vitro/in vivo) studies provided the possible molecular mechanisms of these action.

Where the research disagrees

Whether cinnamon meaningfully improves glycaemic control in type 2 diabetes

• Authors of the 2023 umbrella meta-analysis of 11 meta-analyses, umbrella review of interventional meta-analyses: Cinnamon supplementation was effective in reducing serum FPG (WMD: -10.93 mg/dL; 95%CI: -16.22, -5.65; SMD: -0.86; 95%CI: -1.19, -0.52) (Source 6)
• Cochrane review authors (Leach and Kumar, 2012), Cochrane systematic review of 10 RCTs, 577 participants: There is insufficient evidence to support the use of cinnamon for type 1 or type 2 diabetes mellitus. (Source 8)

Whether coumarin exposure from cinnamon-containing products actually damages the liver at real-world intakes

• EFSA flavourings panel, as reported in a 2020 review of coumarins in food, regulatory toxicological evaluation based on animal data and human medicinal use: Established TDI, based on hepatotoxicity in a two-year dog study, was 0 - 0.1 mg coumarin/kg bw. (Source 2)
• Authors of the 2016 Kampo coumarin study, retrospective clinical cohort of 129 outpatients: Twenty-three patients had an abnormal change in liver function test value, but no significant difference was found in the incidence of abnormal change between the group consuming less than the TDI value (6/31, 19.4%) and the group consuming equal to or greater than the TDI value (17/98, 17.3%). (Source 9)

How much

• Reference intake: No recommended dietary allowance or adequate intake has been set for cinnamon by any body we could reach: it is a culinary spice and flavouring, not an essential nutrient, so there is no reference intake and no deficiency state to correct. (Source 1)
• Upper limit: There is no upper limit for cinnamon itself. For coumarin, the compound in cassia bark that drives the liver concern, EFSA set a tolerable daily intake of 0-0.1 mg per kg body weight in 2004, based on hepatotoxicity in a two-year dog study; the German BfR reached the same figure from human medicinal data. (Source 2)
• Studied: Trials in the Cochrane review gave oral cinnamon monopreparations, predominantly Cinnamomum cassia, at a mean dose of 2 g daily for 4 to 16 weeks. (Source 7)
• Studied: In the Japanese Kampo series, the preparation with the highest coumarin content delivered 5.63 mg of coumarin per day, and patients' median total coumarin intake was 0.113 mg/kg/day. (Source 9)

A common belief, and what the research shows

The belief: Cinnamon is a harmless spice, so taking large amounts as a supplement to lower blood sugar can only help.

What the research shows: Two things are wrong with that. First, the strongest systematic review in the field did not find a benefit: Cochrane reported that "No statistically significant difference in glycosylated haemoglobin A1c (HbA1c), serum insulin or postprandial glucose was found between cinnamon and control groups." Second, dose matters for harm, not just benefit. Most supermarket and supplement cinnamon is cassia, and "In comparison, in Cassia cinnamon, coumarin content is up to 1%, whereas in Ceylon cinnamon is very low (trace), about 0.004%." Coumarin has a European tolerable daily intake set at 0.1 mg/kg because of liver toxicity, and NCCIH notes that "Cinnamon products may not clearly indicate which species (e.g., Ceylon, cassia) or parts (e.g., bark, leaves, roots) of cinnamon have been used in the making of a product." Separately, cinnamon has been the vehicle for lead adulteration: contaminated cinnamon in fruit puree pouches was linked to roughly 500 cases of childhood lead exposure in the United States.

Questions and answers

What is it?

Cinnamon is the bark of trees in the genus Cinnamomum, used for centuries as a spice, a food additive and a traditional remedy. The two types on sale differ chemically: cassia cinnamon and Ceylon or 'true' cinnamon. Supplements are usually concentrated bark powder or extract rather than the whole spice. (Source 11)

What does it do in the body?

In pooled analyses of randomised trials in type 2 diabetes and PCOS, cinnamon was associated with small falls in fasting glucose, insulin, insulin resistance and HbA1c. The HbA1c change was very small, about a tenth of a percentage point. Laboratory and animal studies suggest mechanisms, but those are not human outcomes. (Source 6)

Is it good or bad for you?

It depends almost entirely on amount and species. As a spice in food it is generally regarded as safe; in large or long-term supplement doses it has been linked to gastrointestinal upset, allergic reactions and, through coumarin in cassia bark, to liver concerns. The Cochrane review also found no proven glycaemic benefit, so the risk is not being traded for a demonstrated gain. (Source 12)

How do you get more of it?

Cinnamon comes from the spice itself and from bark supplements. Trials collected in the Cochrane review used oral cinnamon preparations, mostly Cinnamomum cassia, at an average of 2 grams a day for 4 to 16 weeks. That is what was studied, not a recommendation. (Source 7)

If it is harmful, what reduces it?

The component that raises a harm concern is coumarin, not cinnamon as such, and coumarin exposure differs enormously by species. Ceylon cinnamon contains only trace coumarin, around 0.004%, compared with up to 1% in cassia. Reducing exposure therefore means reducing cassia bark intake; there is no procedure in the literature for clearing cinnamon or coumarin from the body once taken. (Source 1)

Why might someone be low in it or missing it?

The question does not really apply. Cinnamon is a spice, not a nutrient the body requires, so there is no such thing as being deficient in it. Someone might consume little or none simply because they do not cook with it; no medical condition, medicine or absorption problem creates a cinnamon requirement. (Source 1)

Which whole foods contain it or feed it?

Cinnamon is itself a whole food: the dried bark, ground or in quills. Cassia is the type most often used in European commercial food products, while Ceylon is more expensive and less common. Because packaging frequently omits the species, the cinnamon in a given product is often unidentifiable from the label. (Source 1)

What happens if you do not have it?

Nothing is known to happen. There is no cinnamon deficiency syndrome, and the strongest systematic review found no proven benefit to replace, concluding that the evidence for using cinnamon in diabetes is insufficient. No trial has reported effects on complications, quality of life or survival either way. (Source 8)

How can you test for it?

No validated clinical test for cinnamon status or cinnamon intake was found in the literature we searched. Trials measure the outcome cinnamon is meant to affect, such as HbA1c or fasting glucose, rather than cinnamon itself; laboratory testing of products for species identity and coumarin content is done by analytical chemists, not by clinicians on patients. (Source 5)

We searched: Searched for cinnamon biomarkers, cinnamaldehyde or coumarin measurement in blood or urine as a status test, and for any diagnostic test in the Cochrane review, the 2021 safety umbrella review, the 2020 coumarins-in-food review and the NCCIH cinnamon page; none describes a validated human test for cinnamon status.

References

1. Foods (MDPI). Coumarins in Food and Methods of Their Determination. 2020. DOI 10.3390/foods9050645. Read the source
2. Foods (MDPI). Coumarins in Food and Methods of Their Determination - tolerable daily intake. 2020. DOI 10.3390/foods9050645. Read the source
3. American Journal of Case Reports. Do cinnamon supplements cause acute hepatitis?. 2015. PMID 25923145. Read the source
4. MMWR Morbidity and Mortality Weekly Report (CDC). Childhood Lead Exposure Linked to Apple Cinnamon Fruit Puree Pouches - North Carolina, June 2023-January 2024. 2024. PMID 39024176, DOI 10.15585/mmwr.mm7328a2. Read the source
5. National Center for Complementary and Integrative Health (NCCIH), NIH. Cinnamon - What Do We Know About Safety? (species labelling and coumarin bullets). 2024. Read the source
6. Diabetology & Metabolic Syndrome. The effect of cinnamon supplementation on glycemic control in patients with type 2 diabetes or with polycystic ovary syndrome: an umbrella meta-analysis on interventional meta-analyses. 2023. DOI 10.1186/s13098-023-01057-2. Read the source
7. Cochrane Database of Systematic Reviews. Cinnamon for diabetes mellitus. 2012. PMID 22972104, DOI 10.1002/14651858.CD007170.pub2. Read the source
8. Cochrane Database of Systematic Reviews. Cinnamon for diabetes mellitus - Authors' conclusions. 2012. PMID 22972104, DOI 10.1002/14651858.CD007170.pub2. Read the source
9. Frontiers in Pharmacology. The Relation between Hepatotoxicity and the Total Coumarin Intake from Traditional Japanese Medicines Containing Cinnamon Bark. 2016. DOI 10.3389/fphar.2016.00174. Read the source
10. Frontiers in Pharmacology. Safety of Cinnamon: An Umbrella Review of Meta-Analyses and Systematic Reviews of Randomized Clinical Trials. 2022. DOI 10.3389/fphar.2021.790901. Read the source
11. Frontiers in Pharmacology. Cinnamomum Species: Bridging Phytochemistry Knowledge, Pharmacological Properties and Toxicological Safety for Health Benefits. 2021. DOI 10.3389/fphar.2021.600139. Read the source
12. National Center for Complementary and Integrative Health (NCCIH), NIH. Cinnamon - What Do We Know About Safety? (first two safety bullets: food amounts, side effects, cinnamon challenge). 2024. Read the source