Spinach and tomato consumption increases lymphocyte DNA resistance to oxidative stress but this is not related to cell carotenoid concentrations

Background The increased consumption of fruit and vegetables has been linked to protection against different chronic diseases, but the dietary constituents responsible for this association have not been clearly identified. Aim of the study We evaluated the effect of spinach and spinach + tomato puree consumption on cell DNA resistance to an oxidative stress. Methods To this aim, in a dietary controlled intervention study, 9 healthy female volunteers consumed a basal diet low in carotenoids (< 600 ug/day) enriched with daily portions (150 g) of spinach (providing about 9 mg lutein, 0.6 mg zeaxanthin, 4 mg beta-carotene) for 3 weeks (from day 0 to day 21) followed by a 2 week wash-out period (basal diet) and finally another 3 weeks (from day 35 to day 56) of diet enriched with daily portions of spinach (150 g) + tomato puree (25 g, providing about 7 mg lycopene, 0.3 mg beta-carotene). At the beginning and the end of each period of vegetable intake, blood samples were collected for lymphocyte separation. Carotenoid concentrations of lymphocytes were determined by HPLC and DNA damage was evaluated by the comet assay following an ex vivo treatment with H2O2. Results During the first period of spinach consumption, lymphocyte lutein concentration did not increase significantly (from 1.6 to 2.2 umol/1012 cells) while lycopene and beta-carotene concentrations decreased significantly (from 1.0 to 0.1 umol/1012 cells, P < 0.001, and from 2.2 to 1.2 umol/1012 cells, P <0.05, respectively). Lutein and lycopene concentrations increased after spinach + tomato puree consumption (from 1.2 to 3.5 umol/1012 cells, P < 0.01, and from 0.1 to 0.7 umol/1012 cells, P < 0.05, respectively). The increase may be attributed to the addition of tomato puree to spinach; however, the different concentrations of carotenoids in lymphocytes registered at the beginning of the two intervention periods may have affected the results. DNA resistance to H2O2 insult increased significantly after both the enriched diets (P < 0.01); however, no “additive effect” was seen after spinach + tomato puree consumption. In the spinach + tomato intervention period an inverse correlation was observed between lymphocyte lycopene concentration and DNA damage, but this seems not able to explain the protection observed. Conclusions The consumption of carotenoid-rich foods even for a short period of time gives protection against oxidative stress. The results obtained seem to suggest that this protective role is not specifically related to carotenoids. However they may contribute together with other substances present in vegetables to lymphocyte resistance to oxidative damage.