Well I don't know where you are getting your facts blackjack (please post pertinent info so we can all learn from it), as most sources say that magnesium deficiency is rare:
http://ods.od.nih.gov/factsheets/magnesium.asp
http://www.nlm.nih.gov/medlineplus/...icle/002423.htm
http://books.nap.edu/openbook.php?r...d=5776&page=196
(I googled dietary magnesium and read the gov and edu sources)
Magnesium is found in a huge variety of foods and about 30% of the average persons magnesium intake is from milk, meat and eggs. A diet low in refined foods should adequately cover any magnesium requirements. It is also interesting to note that a diet low in magnesium will also increase absorption rates of available magnesium.
Early signs of magnesium deficiency include loss of appetite, nausea, vomiting, fatigue, and weakness. As magnesium deficiency worsens, numbness, tingling, muscle contractions and cramps, seizures, personality changes, abnormal heart rhythms, and coronary spasms can occur
I think you would know if you were deficient...
...oh and
"Too much magnesium can cause serious health problems including nausea, vomiting, severely lowered blood pressure, slowed heart rate, deficiencies of other minerals, confusion, coma, and even death. More common side effects from magnesium include upset stomach and diarrhea.
Magnesium competes with calcium for absorption and can cause a calcium deficiency if calcium intake levels are already low."
here