Magnesium may mediate the favorable impact of whole grains on insulin sensitivity by acting as a mild calcium antagonist

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Abstract

Recent epidemiology has linked high consumption of whole grains with reduced risk for diabetes, coronary disease, stroke, and various types of cancer; there is reason to suspect that improved insulin sensitivity is largely responsible for this protection. This phenomenon may be partially explained by the lower glycemic indices of some whole grain food products in comparison to their fiber-depleted analogs. Nonetheless, the fact that whole wheat flour promotes insulin sensitivity relative to white flour – and yet has a near-identical glycemic index – suggests that certain nutrients or phytochemicals in whole wheat, depleted by the refining process, promote preservation of insulin sensitivity. Magnesium is a likely candidate in this regard; magnesium deficiency promotes insulin resistance in rodents and in humans, whereas supplemental magnesium has been found to prevent type 2 diabetes in rodent models of this syndrome, and to improve the insulin sensitivity of elderly or diabetic humans. Magnesium-rich diets as well as above-average serum magnesium are associated with reduced diabetes risk in prospective epidemiology, and with greater insulin sensitivity in cross-sectional studies; moreover, other types of magnesium-rich foods – dairy products, legumes, and nuts – have been linked to decreased diabetes risk in prospective studies. The biochemical role of magnesium in support of insulin function is still poorly understood. In light of evidence that magnesium can function as a mild natural calcium antagonist, it is interesting to note suggestive evidence that increases in intracellular free calcium may compromise the insulin responsiveness of adipocytes and skeletal muscle, and may indeed play a pathogenic role in the insulin resistance syndrome. Thus, it is proposed that some or all of the favorable impact of good magnesium status on insulin function may reflect antagonism of the induction or effects of increased intracellular free calcium. Further research concerning the potential health benefits of long-term magnesium supplementation is clearly warranted. These considerations, however, should not detract from efforts to better inform the public regarding the strong desirability of choosing whole grain products in preference to refined grains.

Section snippets

Whole grains promote insulin sensitivity

There is substantial, steadily accumulating evidence from prospective epidemiology that high dietary consumption of whole grains is associated with decreased risk for diabetes, coronary disease, and stroke [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]. Moreover, many types of cancer are less common, and total mortality in lower, in those with a high intake of whole grains [13], [14], [15], [16]. Cross-sectionally, individuals with a high intake of whole grains tend to have

Does magnesium mediate this benefit?

Whole grains are one of the best dietary sources of magnesium. Other foods which are approximately equally rich in magnesium (on a per-calorie basis) are nuts, legumes, and reduced-fat dairy products. It is unlikely to be a sheer coincidence that high intakes of each of these foods have been linked to decreased diabetes risk in recent prospective epidemiology [35], [36], [37]. Furthermore, high dietary magnesium intake per se was associated with reduced diabetes risk in the Nurses Health Study,

Magnesium may antagonize the adverse impact of intracellular calcium excess

How then does magnesium act to preserve insulin sensitivity? The fact that magnesium acts as a mild physiological calcium antagonist may offer an important clue [47], [67], [68]. Draznin [69] have shown that efficient insulin activity requires an optimal intracellular concentration of free calcium. An undue increase in intracellular free calcium can compromise the ability of insulin to promote efficient glucose uptake. This does not appear to reflect a defect in the signaling pathway that

Practical implications

These considerations suggest that supplemental magnesium, as part of a broader “insurance” program of nutritional supplementation [107], may prove to be a very worthwhile preventive health strategy. Unfortunately, most one-per-day vitamin-mineral supplements in the US mass market provide a rather trivial dose of this nutrient, usually in the less-than-ideal form of magnesium oxide. Magnesium receives very little attention in the popular press (outside of “healthfood” circles), the US government

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