For every cup of raw spinach there is about 24 mg of magnesium and while this may not be an incredibly significant amount, it is still noteworthy and makes this vegetable that much more nutritious to eat. Magnesium is important for the body for a number of reasons, including the fact that it is responsible for over 300 different biochemical reactions and helps promote strong bones as well as regulating your heart rhythm.
This mineral also helps to regulate blood pressure so it is does not become too low or high. When you cook your spinach you effectively increase the amount of magnesium in it, so that is definitely something worth considering when you are trying to get as much as possible from what you eat in terms of overall nutrition. Spinach contains more magnesium when cooked because it is so dense in nature.