> magnesium level reported in a blood plasma test is worthless. This is true, and the reason is more interesting and illuminating than what you stated here. B

> magnesium level reported in a blood plasma test is worthless. This is true, and the reason is more interesting and illuminating than what you stated here. Blood magnesium levels are a significant part of how your body regulates the speed of the heartbeat... so in a normally functioning body they need to be kept pretty constant. So if you don't get enough Mg in your diet, your body will start extracting Mg from tissues and bones keep the levels in your blood high enough. But it will be missed there, because Mg plays important roles there, too, it's just that regulating your heart-beat takes precedence. This is why, if you have any doubts at all that you're getting enough Mg in your diet, it's a good idea to supplement Mg. A bit too much doesn't do any harm, but too little can cause all sorts of problems (especially neurological) but it won't show up on any simple tests as being the cause of those problems. Mg supplements, even the "fancy ones", are relatively cheap... just know that Magnesium Oxide (the most common from in cheap multi-vitamins) is very poorly absorbed and probably useless, but pretty much any other form is fine as a supplement.