The ion magnesium is an absolutely essential element not only to humans but all form of cellular organisms.
Naturally occurring on the earth, magnesium is about 2% of the overall weight of the earth's crust and is a huge component of salt/seawater.
Magnesium helps to regulate cellular nucleic acids, make it indispensable to all life, even plants. In fact, in plants it not only regulates the nucleic acids but is necessary for photosynthesis. The recommended amount for human adults varies by many factors including height, age, weight and gender, but it is a safe assumption that you should consume between 200-300mg of magnesium daily.
Not consuming enough can lead to many health problems, including high blood pressure, diabetes, cardiovascular disease, osteoporosis and anxiety, amongst others. Though some of these are also genetic, not getting enough of this essential element is a big factor as well. Taking too much is also detrimental, so mega-doses are not recommended.
It can cause diarrhea and other bowel problems, which can easily lead to dehydration as well.
Getting the recommended amount is easy if you follow a heart-healthy diet. Common items that are good sources include spinach, nuts, whole grains, peanuts, peanut butter, low-fat milk, black-eyed peas, and breads and pastas that are whole wheat and unprocessed. The more processing a product goes through, the less of this nutrient it has so look for things as close to their natural state as possible. Of course, you can get a multi-vitamin that includes at least the recommended daily amount, though getting it naturally through your diet instead of in pill form is always better.