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Limited evidenceHeart & metabolic

Ceylon Cinnamon

Cinnamon produces small reductions in fasting glucose in type 2 diabetes, but the effect on HbA1c — the outcome that actually matters — is inconsistent across meta-analyses. Almost all trials used cassia rather than Ceylon; Ceylon's real advantage is that it is nearly free of hepatotoxic coumarin, not that it works better.

What the science says

  • Lowers fasting blood glucose Moderate evidence

    A meta-analysis of 10 RCTs (543 patients) using 120 mg to 6 g/day for 4-18 weeks found fasting plasma glucose fell by 24.6 mg/dL (95% CI -40.5 to -8.7). An updated dose-response meta-analysis of 24 RCTs also reported significant reductions in fasting blood sugar and HOMA-IR. Both analyses show substantial between-trial heterogeneity.

  • Effect on HbA1c is inconsistent Limited evidence

    The 2013 meta-analysis found no significant HbA1c change (-0.16%; 95% CI -0.39 to 0.02) despite the fasting glucose drop — a red flag, since HbA1c is the more reliable measure of sustained control. The 2024 update did report a reduction (SMD -0.67; 95% CI -1.18 to -0.15) but with extreme statistical heterogeneity. Diabetes guidelines do not recommend cinnamon for glycaemic control.

  • Ceylon specifically is barely studied Limited evidence

    Nearly every glucose trial used Cinnamomum cassia (Chinese or Saigon cinnamon), not Cinnamomum verum (Ceylon). Ceylon's benefit is extrapolated, not demonstrated. What Ceylon does clearly offer is a far lower coumarin content, which matters for anyone taking cinnamon daily.

  • Modest lipid changes Limited evidence

    The same 10-RCT pool reported total cholesterol -15.6 mg/dL, LDL-C -9.4 mg/dL and triglycerides -29.6 mg/dL, with a trivial HDL-C rise of 1.7 mg/dL. The trials were small, short and heterogeneous, so these numbers should be treated as hypothesis-generating.

Dosage & safety

Studied doseTrials used 120 mg to 6 g/day, most commonly 1-3 g/day of cinnamon powder or a proportionate extract, for 8-16 weeks. Ceylon-specific dosing is unestablished; users generally take 1-2 g/day of ground bark or 250-500 mg of extract.
SafetyThe main safety issue belongs to cassia, not Ceylon: cassia contains high coumarin levels (roughly 1-3 g/kg) which are hepatotoxic in susceptible people. The EFSA tolerable daily intake for coumarin is 0.1 mg/kg body weight/day, and a single teaspoon (about 2.6 g) of cassia powder can exceed that for a 60 kg adult. Ceylon cinnamon contains only trace coumarin, which is the main reason to choose it. Cinnamon can cause oral mucosal irritation, mouth ulcers and contact dermatitis, and cinnamon oil is a strong irritant. It may add to the effect of glucose-lowering drugs — monitor if you take insulin or sulfonylureas. Avoid high-dose supplements in liver disease and in pregnancy, and stop before surgery. Note that "cinnamon" on a supplement label is usually unspecified cassia; look for Cinnamomum verum or zeylanicum explicitly.

Scientific references

Where to buy

Frontier Co-op, Organic Ceylon Cinnamon, 1.76 oz (50 g)

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