Magnesium

Magnesium is the fourth most abundant cation in the body. Almost 60% is found in bone and the rest stored intracellularly.
Magnesium has an effect on many cellular functions, including transport of calcium and potassium, DNA and protein synthesis, energy metabolism, and blood sugar maintenance. It is also important for normal neurological and muscular function, including key involvement in cardiac and smooth muscle contractions (Groff, Gropper et al., 1995).
Most Americans consume less than the estimated average requirement for magnesium. This comes as no mystery when examining the standard American diet - refining foods has removed magnesium from many foods that would have otherwise provided it while fortification practices have not included magnesium when adding back some of the lost nutrients.
For example, olive, corn and peanut oils are all devoid of magnesium, while their whole-food predecessors are rich sources of this mineral.
Similarly, white flour contains far less magnesium than whole-wheat flour (Seelig 2003).
Other significant food sources of magnesium include green leafy vegetables and legumes, which are low in the standard American diet. Additionally, people are consuming less “hard water” (water that contains magnesium and calcium), and more “soft water” or distilled bottled water, shorting them on another historical source of magnesium (Seelig 1980). 

The Magnesium Website (www.mgwater.com) highlights this concept with a quote from Groundwater Resources of British Columbia, Canada:

"According to the U.S. National Academy of Sciences (1977) there have been more than 50 studies, in nine countries, that have indicated an inverse relationship between water hardness and mortality from cardiovascular disease. That is, people who drink water that is deficient in magnesium and calcium generally appear more susceptible to this disease. The U.S. National Academy of Sciences has estimated that a nation-wide initiative to add calcium and magnesium to soft water might reduce the annual cardiovascular death rate by 150,000 in the United States." ( Dr. Harold D. Foster, " Groundwater and Human Health," Groundwater Resources of British Columbia, Ministry of Environment, Lands, and Parks and Environment Canada, pp 6.1-6.3 (reprint), 1994. 

Though only negligible amounts of magnesium are lost in sweat under normal conditions, there is still some evidence that prolonged exertion in hot and humid environments can decrease serum magnesium, which could prove to be clinically significant in individuals with marginal magnesium status.
Additionally, although magnesium levels may return to normal after some training sessions, over a prolonged period of regular exertion, magnesium levels may remain suboptimal. One theory is that elevated metabolic activity, such as that found in prolonged exertion, increases the requirement for magnesium. A plausible mechanism could be increased lipolysis, or the breakdown of fat, which has been shown directly relate to a decrease in plasma magnesium (Rayssiguier, Guezennec et al., 1990).
Dr. Whang, in his paper entitled “Electrolyte and Water Metabolism in Sports Activities,” makes the argument for the addition of magnesium to sports beverages to support healthy circulation, blood sugar control and potassium levels (Whang, 1998).
Furthermore, some researchers have even implicated magnesium loss (and not the traditionally assumed sodium loss) in the pathogenesis of “miner’s cramps” (a condition, also known as “heat cramps,” in which minors, after prolonged exposure to a hot environment, would experience painful cramps when attempting to rehydrate with plain water) (Rayssiguier, Guezennec et al., 1990; Berning and Steen 1998).
Even at the 2008 Superbowl, played at a moderate temperature of the mid-70’s indoors, numerous well-conditioned athletes had to leave the field of play due to muscle cramping.


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