Pooling 12 randomized trials (570 participants), saffron or its constituent crocin lowered fasting glucose by 16.16 mg/dL (95% CI -27.02 to -5.31) and HOMA-IR by 1.19 (95% CI -2.25 to -0.12, five trials). The primary outcome, HbA1c, fell 0.25 percentage points across seven trials, but the interval (-0.58 to 0.08) crossed zero. Heterogeneity was high (I2 61-80%), and fixed-effect sensitivity analyses shrank all three estimates.
The mismatch between outcomes is the story. Fasting glucose can swing with a few weeks of supplementation, yet HbA1c reflects roughly three months of exposure, and it is the marker clinicians use to judge diabetes control and complication risk. A fasting glucose drop of 16 mg/dL without a clear HbA1c shift suggests either short trials, small sample noise, or an effect that is less durable than headline numbers imply. Pooled populations ranged from adolescents with prediabetes to adults with type 1 diabetes and coronary disease, and saffron preparations were not standardized, so the average effect may describe no real patient. Small trials in this field also tend to overstate benefits. This is a preprint that has not been peer reviewed, and its conclusions may change. Existing meta-analyses of herbal glucose-lowering agents show similar patterns of promising fasting markers and weaker long-term data. Treat this as hypothesis-generating: saffron is not a substitute for established diabetes therapy, and anyone on glucose-lowering drugs should consult a doctor before adding it, given hypoglycemia risk. Incremental at best.