Cinnamon Supplements: Dosage, Benefits and Side Effects

Cinnamaldehyde and polyphenolic type-A polymers are the proposed actives, said to improve insulin receptor signalling and slow gastric emptying. Effects on fasting glucose in meta-analyses are real but inconsistent between trials, and one controlled trial in people with impaired glucose tolerance found cassia changed neither insulin sensitivity nor liver enzymes.

• Fasting blood glucose: reduced in dose-response meta-analyses of randomised trials, with considerable heterogeneity.
• Lipids: small improvements in total cholesterol and triglycerides in some analyses.
• HbA1c: less consistent than fasting glucose.

An umbrella review of meta-analyses in metabolic disease is the fairest summary: measurable effects, uneven evidence quality, and results that depend heavily on which trials are included.

A 2023 dose-response meta-analysis of cinnamon on glycolipid metabolism, an updated systematic review and meta-analysis of cassia bark in type 2 diabetes, and a narrative review of coumarin-induced hepatotoxicity. Germany's Federal Institute for Risk Assessment has suggested replacing cassia with Ceylon on coumarin grounds.

1-6 g/day of cinnamon powder in trials, most commonly 1-3 g/day. If you are using cassia rather than Ceylon, coumarin is the constraint rather than the cinnamaldehyde: EFSA's tolerable daily intake for coumarin is 0.1 mg per kg of body weight, which a few grams of cassia can approach or exceed for a smaller adult.

Well tolerated as a food. At supplement doses the concern with cassia is coumarin-associated liver enzyme elevation, which is reversible on stopping. Mouth irritation and allergic reactions occur. Ceylon cinnamon largely removes the coumarin issue.

Additive with glucose-lowering medication. Coumarin in cassia is not the anticoagulant warfarin, but caution alongside anticoagulants is still advised. Anyone with liver disease should avoid high-dose cassia.