If you don't want to play chicken with infections, viruses, and diseases, add an egg or two to your diet daily. Just one large egg contains almost a quarter (22%) of your RDA of selenium, a nutrient that helps support your immune system and regulate thyroid hormones. Kids should eat eggs, especially. If children and adolescents don't get enough selenium, they could develop Keshan disease and Kashin-Beck disease, two conditions that can affect the heart, bones, and joints.