High blood pressure puts a continuous strain on the heart, blood vessels and kidneys. People with untreated high blood pressure can expect kidney problems

... a disabling stroke, chronic illness or death from heart disease. Magnesium supplements have an important and crucial direct and indirect effect on blood pressure and a magnesium deficiency can negatively affect blood pressure. Directly, magnesium makes blood vessels relax and dilate, a vital condition of normal blood pressure. Indirectly, normal magnesium levels are necessary for keeping in balance the electrolytes, or ions (the form in which minerals circulate in the body), that are important for normal blood pressure. These electrolytes are sodium, potassium, magnesium and calcium. Low potassium by itself can cause high blood pressure. But even adequate potassium intake cannot normalize high blood pressure if magnesium is too low. Without enough magnesium and potassium in our bodies, we cannot expect normal blood pressure. Additionally, low magnesium causes a low potassium state, even if potassium intake is adequate. If magnesium is adequate, extra potassium can normalize high blood pressure.

Normal magnesium is also necessary for another indirect effect on blood pressure. It is needed by the cells that form the lining of blood vessels to maintain its normal structure and function. Substances which dilate or open up arteries which help normal blood pressure are increased by magnesium and substances which constrict the arteries and raise blood pressure are inhibited by magnesium.