Strongest evidence: Black cumin shows high-strength evidence for reducing fasting blood glucose (6 of 7 studies beneficial) and hemoglobin A1c (5 of 6 studies beneficial), with moderate effect sizes. For both outcomes, doses ranged from 200–4600 mg/day in populations with type 2 diabetes or metabolic syndrome. Moderate evidence supports small reductions in body weight (4 of 6 studies), body mass index (3 of 5 studies), and systolic/diastolic blood pressure (all 4 studies beneficial). Inflammatory markers like interleukin-6 (4 of 4 studies) and tumor necrosis factor alpha (4 of 4 studies) also show consistent moderate beneficial effects.
Mixed or weaker evidence: Evidence for insulin sensitivity, LDL cholesterol, total cholesterol, and malondialdehyde is moderate but with mixed effect sizes (from small to large). For LDL cholesterol, one meta-analysis in type 2 diabetes patients found no significant effect, suggesting population-specific variation. The limited number of studies (3–4 per outcome) means conclusions remain preliminary for most outcomes beyond glycemic control.
Effective dose patterns: Across outcomes, doses most frequently ranged from 200–4600 mg/day. For inflammatory markers (IL-6), the most-studied range was narrower at 2000–4600 mg/day. No consistent form (oil, powder, extract) was reported across studies, limiting specificity. Study durations were often short (median 7–56 days depending on outcome), so long-term effects are unknown.
Population insights: The strongest effects were seen in adults with type 2 diabetes, metabolic syndrome, or related metabolic disorders for glycemic and weight-related outcomes. For blood pressure and inflammatory markers, effects were observed in diverse populations including postmenopausal women with hypertension and overweight/obese individuals. Evidence in adolescents or general healthy populations is limited.
Notable caveats: A key limitation across all outcomes is potential publication bias — null-result studies are less likely to be published. Most studies did not report specific doses, forms, or durations, and individual trial heterogeneity was often high (e.g., I²=95.7% in one HbA1c analysis). The median study duration was only 7 days for glycemic outcomes, raising questions about long-term efficacy and safety.