Dark greens are great sources of calcium. Calcium is the mineral that makes our bones and teeth strong. It is also needed so that our muscles will contract and helps blood from a cut or wound heal and clot. Spinach and other greens such as kale and chard can contain at least 10% of our daily value requirements for calcium. Spinach is also a great source of iron, which our bodies use to form hemoglobin and myoglobin—these are the proteins that carry oxygen throughout our bodies. Greens are also very high in beta carotene (vitamin A from plants) and vitamin C.