The higher the level ofselenium, as measured in blood serum and toenails, the lower the risk of bladder cancer. Selenium had a significant protective effect mainly among women, which the researchers believe may result from genderspecific differences in this its accumulation and excretion. Several types of mushrooms are rich in this essential trace mineral: 100 grams of raw crimini have 47 percent of your daily needs, cooked shiitakes have 45 percent and raw white button have 17 percent.