Patients may ask whether cinnamon is helpful for diabetes. It doesn't seem to help in type 1 diabetes, BUT it may improve insulin sensitivity and lower glucose in patients with type 2 diabetes. Studies are conflicting. But overall, they suggest that using cinnamon supplements for up to 4 months may modestly lower fasting blood glucose in type 2 diabetes by up to about 25 mg/dL.
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The best evidence comes from a meta-analysis of these clinical trials, which included 543 adults with type 2 diabetes. Results show that taking cassia cinnamon 120 mg to 6 grams daily for 4-18 weeks reduces fasting blood glucose by an average of 25 mg/dL, total cholesterol by 16 mg/dL, low-density lipoprotein (LDL) cholesterol by 9 mg/dL, and triglycerides by 30 mg/dL, and increases high-density lipoprotein (HDL) cholesterol by 2 mg/dL. Cassia cinnamon has no effect on glycated hemoglobin (HbA1c).
As a pharmacist, emphasize lifestyle changes, metformin, and other diabetes medications. But if patients wish to try cinnamon, point them to cassia cinnamon, sometimes called Chinese cinnamon, Cinnamomum aromaticum, or Cinnamomum cassia. This is the type shown to decrease glucose in humans.
Explain that most studies used 1 to 3 g/day of cassia cinnamon capsules or as an extract in a dose of 250 mg twice daily. Point out that the typical cinnamon spice sold in grocery stores may contain varieties that haven't been shown to be beneficial for diabetes. Recommend stopping cinnamon if it doesn't help after 3 to 4 months. Explain cinnamon is usually well tolerated. Be aware, cassia cinnamon contains coumarin, which is linked to liver toxicity at high doses, but this isn't usually a concern with typical cinnamon doses.
REFERENCES
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Costello RB, Dwyer JT, Saldanha L, Bailey RL, Merkel J, Wambogo E. Do Cinnamon Supplements Have a Role in Glycemic Control in Type 2 Diabetes? A Narrative Review. J Acad Nutr Diet. 2016 Nov;116(11):1794-1802. Available: https://pubmed.ncbi.nlm.nih.gov/27618575
Allen RW, Schwartzman E, Baker WL, Coleman CI, Phung OJ. Cinnamon use in type 2 diabetes: an updated systematic review and meta-analysis. Ann Fam Med. 2013 Sep-Oct;11(5):452-9. Available at: https://pubmed.ncbi.nlm.nih.gov/24019277