This essential trace mineral is used for usual bodily functions including the maintenance and protection of hair and nails. It also contributes to the regular function of the immune system and fights against oxidative stress by protecting cells. Furthermore, selenium helps to maintain standard thyroid function and contributes to usual fertility and reproduction. This mineral contains proteins called selenoproteins and these are found in a variety of healthy foods like garlic, spinach and broccoli. Selenium can also be found in soil and water.