Spinach, radicchio and watercress may not immediately come to mind as foods for keeping bones strong, but all contain lots of vitamin K. A study at Tufts University in Boston found that low dietary intake of vitamin K in women was associated with low bone mineral density. (The study didn’t find a link in men.) Just one cup (250 mL) of chopped watercress has 100 percent of your daily vitamin K; radicchio, 120 percent; and spinach, 170 percent.