Interaction between green tea and metformin and its effects on oxidative stress and inflammation in overweight women: a randomised clinical trial

Abstract This study evaluated the effect of green tea extract and metformin and its interaction on markers of oxidative stress and inflammation in overweight women with insulin resistance. After screening, 120 women were randomly allocated in 4 groups: Placebo (PC): 1g of microcrystalline cellulose/day; Green tea (GT): 1 g (558 mg polyphenols) of standardized dry extract of green tea/day and 1 g of placebo/day; Metformin (MF): 1 g of metformin/day and 1 g of placebo/day; Green Tea and Metformin (GTMF): 1 g (558 mg polyphenols) and 1 g of metformin/day. All groups were followed-up for 12 weeks with assessment of oxidative damage to lipids and proteins, specific activity of antioxidant enzymes and inflammatory cytokine serum levels. The association of green tea with metformin significantly reduced IL-6 (GTMF: –29.7((–62.6)–20.2))( p = 0.004). Green tea and metformin isolated reduced TNF-α (GT: –12.1((–18.0)–(–3.5)); MF: –24.5((–38.60)–(–4.4)) compared to placebo (PB: 13.8 (1.2–29.2))( P < 0.001). Also, isolated metformin reduced TGF-β (MF: –25.1((–64.4)–0.04)) in comparison to placebo (PB: 6.3((–1.0)–16.3))( p = 0.038). However, when combined, their effects were nullified either for TNF-α (GTMF: 6.0((–5.7)–23.9) and for TGF-β (GTMF: –1.8((–32.1)–8.5). This study showed that there is a drug-nutrient interaction between green tea and metformin that is dependent on the cytokine analyzed.