A new systematic review and meta-analysis of 23 randomized trials found that regular tea consumption produces a statistically significant improvement in glycemic control among people with type 2 diabetes. Wine and plain water showed no such effect. The benefit of tea is real but small — and it does not replace drug therapy.
The authors set out to answer a question that interests almost everyone living with diabetes: do specific beverages help keep blood sugar under control? Until now the data were scattered — some studies praised green tea, others argued over wine and water. The team systematically searched PubMed and Web of Science through April 27, 2026, and selected only randomized controlled trials (RCTs), the gold standard of evidence-based medicine.
The final analysis included 23 RCTs with 1,368 participants who had type 2 diabetes. Beverages were grouped into four categories: tea, wine, water, and "other" (beetroot juice, omega-3, and a high-fiber diet with coffee). The primary outcome was glycated hemoglobin (HbA1c) — a marker of average blood sugar over the previous 2–3 months. Effect size was quantified with the standardized mean difference (Hedges' g), and between-study heterogeneity with the I² statistic.
Overall, beverage interventions significantly reduced HbA1c compared with controls: Hedges' g = −0.37 (95% CI: −0.58 to −0.16; p < 0.001). On the effect-size scale this is a small effect (0.2 = small, 0.5 = medium, 0.8 = large). But the averaged number hides important differences between beverages:
| Beverage | RCTs | Effect (Hedges' g) | Significance |
|---|---|---|---|
| Tea | 12 | −0.34 (−0.55…−0.13) | Significant (p = 0.001) |
| Wine | 5 | −0.15 (−0.86…0.56) | None (p = 0.68) |
| Water | 3 | −0.36 (−0.94…0.22) | Trend, not significant (p = 0.22) |
| Other* | 3 | −0.54 (−1.06…−0.02) | Significant (p = 0.04) |
*Beetroot juice, omega-3, and a high-fiber diet with coffee.
Only tea showed a consistent, significant effect with moderate heterogeneity (I² = 40%). The "other" beverages also worked, but they rest on just three heterogeneous studies. Wine and water did not produce a reliable result.
If you have type 2 diabetes, a cup of unsweetened tea is a simple, cheap, and safe addition to your diet that may slightly help blood sugar control. The key is tea without sugar or cream: a sweetened drink would cancel out any benefit. An HbA1c reduction of a small-effect magnitude corresponds on average to a drop of roughly 0.2–0.3 percentage points — meaningful statistically, but not enough to abandon prescribed treatment.
The main practical takeaway: tea is a "bonus," not a "replacement." The authors explicitly stress that beverages should not displace proven therapy — metformin, insulin, diet, and physical activity. Wine showed no benefit for blood sugar, and given the well-known risks of alcohol in diabetes, treating it as "medicinal" is certainly not advisable.
The quality of evidence is limited. Only 1 of the 23 studies (4.3%) was rated as overall low risk of bias on the Cochrane RoB 2.0 tool, while 82.6% of the trials raised "some concerns." Overall heterogeneity was high (I² = 71.6%), meaning the studies differed considerably in design, tea types, doses, and duration. That means the averaged figure cannot be read literally for any specific kind of tea. The authors call for higher-quality, longer-term RCTs.
⚠ This is a preprint. The work was posted on the Research Square server and has not yet undergone peer review. Its conclusions may change after expert evaluation. Do not change your diabetes treatment plan without consulting your doctor.
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