What clinical evidence supports cinnamon (Ceylon or Cassia) for blood‑sugar control and what doses were used?
Executive summary
Clinical trials and meta-analyses provide mixed but measurable evidence that cinnamon—both commercial Cassia preparations studied historically and newer Ceylon (C. zeylanicum) extracts—can lower measures of glycemia (fasting glucose, HOMA-IR and in some analyses HbA1c) with effect sizes that vary by study and formulation; reported study doses range from about 0.5 g/day up to 6 g/day, with many modern randomized trials clustering around 0.5–1.5 g/day [1] [2] [3] [4]. The totality of evidence shows statistically significant reductions in some pooled analyses but high heterogeneity across trials and inconsistent findings in individual studies, so cinnamon cannot be declared a universally effective glycemic therapy based on current data [5] [4] [6].
1. What the clinical literature actually shows about efficacy
Multiple meta-analyses and systematic reviews conclude cinnamon supplementation produces statistically significant reductions in fasting blood glucose and insulin resistance metrics in people with type 2 diabetes or prediabetes, and some report modest reductions in HbA1c, but results are heterogeneous: one umbrella meta-analysis pooling prior interventional meta‑analyses found significant reductions in fasting glucose, HOMA‑IR and HbA1c across 24 RCTs [4], while earlier reviews noted small trials with conflicting results and substantial between‑study heterogeneity that limit definitive conclusions [5] [6].
2. How large the effects are, practically speaking
Effect sizes vary by outcome and meta‑analysis methods; pooled estimates have shown meaningful reductions in fasting glucose and HOMA‑IR (for example, standardized mean differences indicating benefit in pooled RCTs) and weighted mean differences of roughly −0.545 mmol/L for fasting glucose in one meta‑analysis, but the magnitude and clinical importance differ across populations and trials and are tempered by high I2 values indicating inconsistency between studies [6] [4] [5].
3. Which cinnamon types and formulations were tested
Trials have evaluated crude cinnamon bark powder (often Cassia in early studies) and standardized extracts including water‑soluble preparations; more recent randomized controlled trials have explicitly tested Cinnamomum zeylanicum (Ceylon) extracts as well as generic “cinnamon” capsules, and authors note that type of cinnamon and extraction method may influence outcomes—an acknowledged source of heterogeneity in meta‑analyses [1] [7] [5].
4. What doses were used in trials (and which showed effects)
Clinical trials used a wide dose range: the influential early Khan et al. trial tested 1, 3 and 6 grams/day of Cassia and reported dose‑related reductions after 40 days [1]; many later RCTs used 500 mg capsules administered twice daily or three times daily (i.e., 1.0–1.5 g/day) for 8–12 weeks and reported variable glycemic benefits [2] [3] [8]. A PLOS One trial and other authors cite benefits at about 500 mg/day to 500 mg twice daily over 8–12 weeks in some populations [7] [2]. Trials in prediabetes have also used seasoning‑level doses and found lower 24‑hour glucose profiles in a crossover study, though that trial described the dose as “amount commonly used for seasoning” rather than a precise gram value in the provided abstracts [9] [10].
5. Strengths, limitations and safety signals in the evidence
Strengths include multiple RCTs and meta‑analyses showing consistent directionality in glycemic outcomes for some measures; limitations are small individual trial sizes, varied populations (T2D, prediabetes, obesity), non‑standardized cinnamon types and preparations, short durations, and high statistical heterogeneity across studies that weakens causal claims [5] [4] [6]. Some trials report favorable anthropometric and lipid effects alongside glycemic changes, but generalizability and long‑term safety remain incompletely characterized in the cited literature [2] [7]. The sources provided do not supply a comprehensive safety profile or address long‑term risks for specific cinnamon species in depth, so definitive safety statements cannot be made from these documents alone [7] [1].
6. Bottom line for clinicians and patients (evidence‑based take)
Cinnamon supplementation has modest, sometimes statistically significant effects on fasting glucose and insulin resistance in pooled analyses and several RCTs, with commonly tested doses roughly 0.5–1.5 g/day and historical studies up to 6 g/day showing effects; heterogeneity in cinnamon type, dose, and trial design prevents universal recommendations, and the evidence supports cautious, adjunctive use in controlled settings while awaiting larger, standardized trials [4] [1] [3].