This article covers the importance of and issues surrounding getting adequate magnesium. They make quite strong claims about magnesium:
Of course no single nutrient stands alone in relation to the body, and the first priority is to eat a varied diet of whole plant and animal foods from the best sources near you. Adding extra magnesium, however, might be the missing nutritional link to help us guard against heart disease, stroke, depression, osteoporosis and many other disorders. In the prevention and alleviation of these diseases, magnesium can be truly miraculous.
Abstract: There are two types of nutrient deficiencies, frank deficiencies (such as scurvy from ascorbic acid deficiency or goitre from iodine deficiency) and subclinical deficiencies (a clinically silent reduction in physiological, cellular and/or biochemical functions). It is the latter that is most concerning as it is hard to diagnose and predisposes to numerous chronic diseases.
Because serum magnesium does not reflect intracellular magnesium, the latter making up more than 99% of total body magnesium, most cases of magnesium deficiency are undiagnosed. Furthermore, because of chronic diseases, medications, decreases in food crop magnesium contents, and the availability of refined and processed foods, most people in modern societies are at risk for magnesium deficiency.
Certain individuals will need to supplement with magnesium to prevent suboptimal magnesium deficiency, especially if trying to obtain an optimal magnesium status to prevent chronic disease. Subclinical magnesium deficiency increases the risk of numerous types of cardiovascular disease, costs nations around the world an incalculable amount of healthcare costs and suffering and should be considered a public health crisis. That an easy, cost-effective strategy exists to prevent and treat subclinical magnesium deficiency should provide an urgent call to action.