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Evidence-Based Supplement Research
Evidence-Based Supplement Research
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Red Grape

What does the research say about Red Grape?

4 health outcomes synthesised

Red grape and its extracts—including grape seed extract and mixed flavonoids—have been researched across 4 health outcomes, primarily related to liver function and blood pressure. The strongest evidence, graded as moderate, comes from 4 studies on reducing aspartate aminotransferase (AST) levels in people with NAFLD and thalassemia, suggesting small beneficial effects. Doses in the research range from 100 to 520 mg/day, with study durations typically between 4 and 8 weeks.

Strongest evidence: The outcome with moderate evidence strength is reduced aspartate aminotransferase (AST) level. Among 4 studies (3 beneficial, 1 neutral), the predominant effect was small, though one moderate effect was seen. The research focused on clinical populations (NAFLD and thalassemia with iron overload) over a median of 44 days, with doses varying between 100 and 520 mg/day.

Mixed or weaker evidence: Three other outcomes have low evidence strength. For systolic blood pressure, 2 of 3 studies found small beneficial effects (1 neutral), with one effective dose of 520 mg/day grape seed extract reported. For diastolic blood pressure, all 3 studies were beneficial but effect sizes were mixed (small to moderate); the evidence base is small and subject to publication bias. For alanine aminotransferase (ALT) level, 2 of 3 studies found beneficial effects (small to moderate), but the neutral study used quercetin in thalassemia patients, suggesting population- or form-specificity. All low-strength conclusions are preliminary due to small sample sizes and limited numbers of studies.

Effective dose patterns: A dose of 520 mg/day of grape seed extract appears across multiple outcomes—systolic blood pressure, diastolic blood pressure, and ALT reduction—but was reported in only one or two trials each. No single effective dose was confirmed across all studies; doses in the AST research ranged from 100 to 520 mg/day. The lack of standardized dosing limits cross-outcome comparisons.

Population insights: Most studies enrolled people with non‑alcoholic fatty liver disease (NAFLD). One AST study included thalassemia patients with iron overload. Blood pressure studies focused on males with elevated or stage 1 hypertension and NAFLD patients. Generalizability to broader populations (e.g., healthy adults, other ethnicities) is uncertain.

Notable caveats: The evidence base for all outcomes is small (3–4 studies each), so conclusions are preliminary. Publication bias is a concern for blood pressure research. Some studies used mixed flavonoids (e.g., quercetin, curcumin, bilberry) alongside grape seed extract, making it difficult to attribute effects solely to red grape. Study durations were short (≥7 days up to 60 days), and sample sizes were small (n=25–30 in some RCTs). These limitations caution against overgeneralizing the findings.

Frequently asked

  • What is Red Grape good for according to research?
    Red grape and its extracts (including grape seed extract) have been studied for four health outcomes: reducing aspartate aminotransferase (AST) level, reducing alanine aminotransferase (ALT) level, reducing systolic blood pressure, and reducing diastolic blood pressure. The strongest evidence (moderate strength) supports a small beneficial effect on AST levels in people with NAFLD or thalassemia. For blood pressure and ALT, the evidence is weaker (low strength) and considered preliminary.
  • What dose of Red Grape is typically used in studies?
    Reported doses vary widely across studies. For AST reduction, doses ranged from 100 to 520 mg/day. For blood pressure and ALT reduction, the most commonly specified dose was 520 mg/day of grape seed extract, observed in a single RCT. Many studies did not fully report dose information, so a consistent effective dose has not been established.
  • Who benefits most from Red Grape?
    The research primarily enrolled clinical populations: people with non‑alcoholic fatty liver disease (NAFLD) for liver enzyme outcomes, thalassemia patients with iron overload for AST, and males with elevated or stage 1 hypertension for blood pressure outcomes. Effects may be specific to these groups, and generalizability to healthy individuals or other demographics is unclear.
  • Are there caveats or limitations in the research on Red Grape?
    Yes, important caveats include the small number of studies (3–4 per outcome), small sample sizes (e.g., n=25–30 in some trials), short durations (7–60 days), and the use of mixed extracts (e.g., bilberry, quercetin, curcumin) alongside grape seed, making it hard to isolate red grape’s specific effects. Publication bias is a concern, especially for blood pressure research. All conclusions should be considered preliminary.
  • Does Red Grape help with blood pressure?
    Three studies each examined systolic and diastolic blood pressure. All three found beneficial effects on diastolic blood pressure (effect sizes small to moderate), while for systolic blood pressure, two of three studies reported small beneficial effects and one found neutral effects. However, the evidence strength is low, and the body of research is small, so these findings are not conclusive.
  • Does Red Grape help with liver enzymes?
    For aspartate aminotransferase (AST), 3 of 4 studies reported beneficial effects with moderate evidence strength. For alanine aminotransferase (ALT), 2 of 3 studies reported beneficial effects but with low evidence strength. Beneficial effects on AST and ALT were observed primarily in NAFLD patients. The ALT finding is limited by one neutral study that used a different flavonoid (quercetin) in a different population.

Most-studied combinations with Red Grape

most supplement research is combination research
Also studied with:Turmeric (2), Ginkgo (2), Thistle (2)
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