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Investing in Nutrient Dense Food: Magnesium

The last nutrient I'll focus on in this series is magnesium. Magnesium, like iron and calcium, is a mineral rather than a vitamin, and it serves a range of purposes in our bodies. Among them, magnesium serves as a cofactor in hundreds of enzyme systems that regulate a range of biological processes, including protein synthesis, muscle and nerve function, blood sugar control and blood pressure regulation, among others [1]. It also contributes to the structural development of bones and teeth, and aids in the transport of calcium and potassium across cell membranes. Magnesium deficiencies have been linked to high blood pressure, heart disease and diabetes, among other ailments [2].

Magnesium is present in a wide range of foods of both plant and animal origin. The graph below shows the cost of meeting a daily allowance of 400 mg of magnesium from several foods, with data on nutrient contents taken from the USDA's National Nutrient Database and prices recorded from recent visits to my local farmers' market and grocery cooperative [3]. These prices reflect certified organic produce, and grass fed and pasture raised animal foods.

Based on USDA data the most cost-effective sources of magnesium are plant-based, including almonds, potatoes, spinach, cabbage and sweet potatoes. All of these sources provide a daily allowance of 400 mg magnesium for less than $10. Animal derived foods like organ and muscle meats are far more costly per unit magnesium, as are fruits. As with calcium though, the data provided by the USDA doesn't tell the whole story. Many factors influence the degree to which our bodies can absorb magnesium from the food we eat. The presence of anti-nutrients such as phytate in seeds like almonds reduces the availability of magnesium and other minerals, making these foods less of an ideal source than a simple mineral analysis might initially suggest [4]. As with calcium though, resistant starch increases the absorbability of magnesium.

It's also true that, in pursuit of higher yields for many fruits and vegetables, nutrient density of foods have declined in the US and elsewhere [5]. This reality is exacerbated by decades, if not centuries, of abusing prime agricultural soils such that many are depleted in magnesium and other minerals, making it all but assured that food grown in or animals raised on those soils will be depleted of the nutrient. Given this reality, it can be helpful to supplement our magnesium intakes with non-food sources of magnesium, and one such source is bathing in mineral salts, particularly epsom salts (magnesium sulfate). Although I make a point to eat a wide array of fresh vegetables that offer resistant starch to help maintain a good magnesium status, I also take baths in epsom salts a few times each week as a mineral supplement since magnesium is readily absorbed through the skin [6]. A cautionary note on this habit though: those who take this method too far and supplement daily with large quantities of epsom salts, particularly when taken as a gargle, risk overdose [7]. So be cautious with supplementation, not just of magnesium but with any mineral.

Notes

  1. Magnesium: Fact Sheet for Health Professionals. National Institutes of Health, United States Department of Health and Human Services.
  2. A. Rosanoff, et al. (2012) Suboptimal magnesium status in the United States: are the health consequences underestimated? Nutritional Review, Vol. 70, Pgs. 153-164.
  3. National Nutrient Database for Standard Reference. United States Department of Agriculture, Agricultural Research Service.
  4. C. Coudray, et al. (2003) Effects of dietary fibers on magnesium absorption in animals and humans. The Journal of Nutrition, Vol. 133, Pgs. 1-4.
  5. B. Halweil (2007) Still No Free Lunch: Nutrient Levels in U.S. Food Supply Eroded by Pursuit of High Yields. Report for The Organic Center.
  6. R. Waring, et alReport on Absorption of Epsom Salts (Magnesium Sulfate) Across the Skin. Report for the Epsom Salts Council.
  7. R. Birrer, et al. (2002) Hypermagnesemia-induced fatality following epsom salt gargles. The Journal of Emergency Medicine, Vol. 22, Pgs. 185-188.

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