Cinnamon

What it is

Cinnamon is the dried inner bark of Cinnamomum trees. The two main types are Ceylon (true) cinnamon, from Sri Lanka, and cassia, which is cheaper and more widely sold in supermarkets and supplements.

Cinnamon supplements are marketed for blood sugar control and weight. The difference between the types matters because cassia contains much more coumarin.

How it works

Cinnamon compounds, including cinnamaldehyde and polyphenols, may improve insulin signalling and slow digestion of carbohydrates in lab and some human studies. The effect is not large or consistent.

What the evidence says

• Limited Fasting blood sugar in type 2 diabetes
  Reviews show small average reductions, but trials vary a lot in quality and results are inconsistent.
• Limited HbA1c (long-term blood sugar)
  Little or no consistent effect in better-quality trials.
• Weak Cholesterol and blood pressure
  Small changes in some trials, not reliable.
• Weak Weight loss
  No meaningful evidence.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Using cinnamon as a spice in food is safe for most people.
• Supplement trials use around 1-6 g of powder a day, which for cassia can exceed the tolerable daily intake for coumarin in some people.
• European food safety authorities set a tolerable daily intake of about 0.1 mg of coumarin per kg of body weight; check current guidance.
• Ceylon cinnamon contains only trace coumarin.

Forms and what to look for

• Ceylon cinnamon (Cinnamomum verum): lower coumarin, usually pricier, and the better choice for regular use.
• Cassia (C. cassia, C. aromaticum or Chinese cinnamon): high in coumarin; fine occasionally in cooking, less so as a daily supplement.
• Water-soluble extracts are used in some trials and have lower coumarin.
• Check the label for the species; many just say cinnamon, which is usually cassia.

What to expect, and when

• Trials run 4-16 weeks.
• Effects, if any, are small.
• You will not feel blood sugar changes, so anyone with diabetes should rely on regular monitoring.

Side effects

• Mouth irritation or sores with large amounts, especially from cinnamon oil.
• Stomach upset.
• Allergic skin reactions, particularly with cinnamaldehyde.
• Low blood sugar in people on diabetes medicines.
• Liver enzyme elevations with high coumarin intake.

Interactions

• Diabetes medicines: possible additive effect on blood sugar.
• Hepatotoxic medicines or supplements: coumarin may add to liver load.
• Anticoagulants: coumarin is chemically related to warfarin, though cinnamon coumarin is not an anticoagulant in the same way; caution is still advised.
• Check with a pharmacist if you take regular medicines.

Who should avoid it

• People with liver disease.
• Daily high-dose cassia users, who are most at risk of exceeding coumarin limits.
• People with diabetes who adjust medicines without medical advice.
• Pregnancy at supplement doses.
• Children eating large amounts of cassia, who have lower limits by body weight.

Risks and safety

• Coumarin intake from cassia can exceed the tolerable daily intake with just a teaspoon or two a day for some people.
• Cinnamon challenge style fads (swallowing dry powder) can cause choking and lung injury.
• Some products labelled as cinnamon are cassia, with variable coumarin levels.

Buying well: quality and testing

• Look for Ceylon or Cinnamomum verum on the label.
• Third-party testing (USP, NSF, Labdoor) can confirm contents.
• Beware of megadose claims.
• Choose products stating mg of cinnamon per capsule.

Bottom line

Cinnamon on your porridge is lovely and harmless. Cinnamon as a blood sugar supplement is a small, uncertain gain, and the cassia variety adds a coumarin issue. If you do want to supplement, use Ceylon, stay near label doses and do not use it to replace diabetes treatment.