What doses and preparations of cinnamon were used in randomized trials showing benefit for fasting glucose?

1. What the randomized trials actually tested: dose ranges and duration

Clinical randomized controlled trials of cinnamon and fasting glucose enrolled interventions spanning from modest milligram doses to multi-gram daily intakes — pooled trial tables show dosing reported from about 120 mg per day up to 6 g per day — and most studies lasted between roughly 4 and 18 weeks, meaning the positive fasting‑glucose signals come from short‑to‑medium term supplementation rather than long‑term outcome trials ^{[1] [3]}.

2. Two broad preparation families: whole spice versus extracts

The literature clusters into two preparation types: raw cinnamon powder (the ground bark used as a culinary spice) and aqueous or water‑soluble cinnamon extracts (branded or standardized supplements); meta-analyses and trial reports explicitly note trials used both “aqueous cinnamon extract or raw cinnamon powder” and that some analyses separated extract-only effects from whole-cinnamon effects ^{[1] [2]}.

3. Extracts often concentrated — and sometimes standardized

Several trials used commercially prepared, water‑soluble cinnamon extracts such as Cinnulin PF® or other extract formulations intended to isolate polyphenolic fractions; trial protocols investigating these extracts specify concentrated doses designed to deliver active constituents at lower mass than whole‑powder grams, and some registered protocols (e.g., a water‑soluble cinnamon extract trial) were designed to test extract plus lifestyle intervention versus placebo ^{[4] [1]}.

4. Gram‑level culinary doses also showed effects in some trials

Older and influential trials that found fasting‑glucose reductions often used gram‑level daily dosing — for example, several trials and meta‑analyses cite 1–3 g/day ranges and up to about 6 g/day of whole cinnamon powder producing statistically significant reductions in fasting plasma glucose in pooled analyses ^{[2] [1] [5]}.

5. Evidence that extracts vs whole cinnamon may differ but findings are mixed

Meta-analytical work reports that both cinnamon extract and whole cinnamon intake were associated with lower fasting glucose in pooled data, and one meta‑analysis specifically found extract-only analyses also lowered fasting glucose; however, heterogeneity between studies (formulation, dose, duration, baseline glucose) is high, so it is not definitive that one form is categorically superior ^{[2] [6] [3]}.

6. Why heterogeneity matters: variable formulation, dosing, and trial quality

Authors of systematic reviews and dose‑response meta‑analyses warn the trials differ in species used, preparation (powder vs aqueous extract), dose (120 mg–6 g/day), outcome measurement, and co‑therapies, producing high I2 values and potential publication bias in fasting‑glucose analyses; those limitations mean the observed pooled benefit is real in meta‑analytic statistics but hard to translate into a single recommended dose or product ^{[1] [6] [3]}.

7. Practical implications and unanswered questions

The evidence supports that both gram‑level culinary cinnamon and concentrated water‑soluble extracts have been used successfully in randomized trials to lower fasting glucose over weeks to a few months, but because trials used different preparations, doses, and durations, and some used standardized extracts while others did not, no single universally validated dose‑form emerges from the literature — further standardized trials comparing defined extract concentrations against measured amounts of whole powder over longer follow‑up are explicitly recommended by the reviews ^{[1] [3] [7]}.