Berries and oxidative stress markers: an overview of human intervention studies
Berries are an excellent source of bioactive compounds such as vitamins, minerals but above all polyphenols with anthocyanins as the most representative compounds. Several in vitro and in vivo studies documented the beneficial effects of berries and their bioactives in the modulation of numerous cell functions related to oxidative stress and/or antioxidant protection. The following review summarizes published results about the role of berries (either fresh, juice, freeze-dried or dehydrated) on total plasma and serum antioxidant status and on the modulation of biomarkers of oxidative stress in acute and chronic human intervention trials. The biomarkers considered include DNA, protein and lipid oxidation, and endogenous antioxidant enzymes. Though limited, there is indication that the consumption of berries may reduce oxidative stress by modulating protein and lipid oxidation, and by improving total antioxidant status. In particular, these effects are more evident following chronic dietary interventions with respect to postprandial studies. Benefits are observed in healthy subjects as well as in those with cardiovascular risk factors or other diseases. On the contrary, data regarding the effect of berries on DNA damage and endogenous antioxidant enzyme activities are still scarce and inconclusive. In conclusion, much remains to be elucidated before a comprehensive understanding of the effects of berries on the modulation of oxidative stress markers is achieved. Robust clinical evidence supporting the role of berries in counteracting oxidative stress in humans is encouraged.