FMD , serum levels of isoprostanes , nitrite/nitrate ( NOx ) and sNOX2-dp , a marker of blood NOX2 activity , maximal walking distance ( MWD ) and maximal walking time ( MWT ) were studied in 20 PAD patients ( 14 males and 6 females , mean age : 699 years ) randomly allocated to 40 g of dark chocolate ( > 85 % cocoa ) or 40 g of milk chocolate ( 35 % cocoa ) in a single blind , cross-over design .