Magnesium is a mineral that is important for normal bone structure in the body. People get magnesium from their diet, but sometimes magnesium supplements are needed if magnesium levels are too low. Dietary intake of magnesium may be low, particularly among women. Magnesium deficiency is also not uncommon among African Americans and the elderly. Low magnesium levels in the body have been linked to diseases such as osteoporosis, high blood pressure, clogged arteries, hereditary heart disease, diabetes, and stroke.