Oral Magnesium and Wellness: Increased RDAs and Preventive Medicine

THE MAGNESIUM REPORT
CLINICAL, RESEARCH, AND LABORATORY NEWS FOR CARDIOLOGISTS
FIRST QUARTER 2000

Oral Magnesium and Wellness: Increased RDAs and Preventive Medicine

RONALD J. ELIN, MD, PHD, AND ROBERT K. RUDE, MD

Traditionally, preventive medicine means elective stress testing, mammography, screening for prostate-specific antigen, and periodic lipid profiling. It also suggests an intent to be proactive about lifestyle and behavior changes, including diet and nutrient supplementation. Now we have evidence to add adequate intake of magnesium—the "forgotten electrolyte"—to our list of preventive health measures.

Ensuring adequate magnesium intake, either through dietary sources of magnesium or the use of oral magnesium supplements, constitutes a major step toward "wellness" that is justified by scientific and clinical data. Both the graying of America and the growing emphasis on exercise and fitness are reasons to take extra care that magnesium intake is adequate. Suboptimal intake of magnesium has been associated with a number of extremely prevalent and potentially serious conditions. In addition, a substantial portion of the American population is at risk for chronic latent magnesium deficiency, which itself is a risk factor for these and other conditions.

Why is chronic latent magnesium deficiency important, and what can be done about it? For an answer, it is helpful to consider the present Recommended Daily Allowance (RDA) of magnesium and why it was increased.

1997 RDAs: The new standard

The RDA is the dietary intake that would provide an adequate amount of a nutrient for nearly all the population. In practical terms, this boils down to approximately 97% to 98% of the entire population. RDAs are specific to life stages and gender.

Among the most potent reinforcements of the message that magnesium is an essential nutrient for good health is the recent endorsement of higher RDAs by the Institute of Medicine and the National Academy of Sciences. As of 1997, the RDA of magnesium was raised 15%, to approximately 6 mg/kg/d. For men, this means an increase from 350 mg/d to 420 mg/d, and for women from 280 mg d to 320 mg/d (Table 1).

Wellness Table 1

The National Academy of Sciences and the Institute of Medicine reevaluate RDAs and their supporting data every decade. Review of scientific information motivated the magnesium intake upgrade promulgated by the Institute of Medicine in its 1997 Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. The experimental data on magnesium come from dietary balance studies involving several different magnesium intake levels under conditions in which diets were either constant and controlled at clinical research centers or self-selected in the community.

These studies, which were thought to provide a more accurate and reliable estimate of dietary magnesium sufficiency involved men and women of all ages—adolescence through older adulthood. Magnesium content of foods was measured using atomic absorption spectroscopy, and the study period was preceded by at least a 12-day lead-in period to allow equilibration of magnesium in the body. Earlier less accurate studies, in contrast, relied on colonmetric methods for assessing magnesium content and required, a lead-in period of as little as 2 days.

The estimated average requirement (EAR), on the other hand, is the nutrient intake estimated to meet the need for a nutrient in 50% of the population. The EAR is among the factors on which the RDA is based. While the EAR is determined from population studies, the RDA is intended for advising individuals about dietary needs. The current EAR corresponds to the previous (now outdated) RDA 350 mg/d for men and 265 mg/d for women.

How Americans stack up

The upgrade in desired intake contrasts starkly to the reality of population-based studies. Estimates suggest that between 50% and 85% of the population of the United States is receiving an inadequate magnesium intake. In a 1977-1978 study of almost 40,000 people, magnesium consumption met or exceeded the RDA (which at that time was 5 mg/kg/d) in only 25% of those surveyed. Many studies then showed that the average dietary intake in adults ranged between 43.3% and 93.0% of that RDA, which was low by present standards.

Today the proportion of individuals consuming their RDA of magnesium remains low. Most people take in around 300 mg/d—estimates range from below 300 mg/d to around 325 mg/d. According to the US Department of Agricultures 1994 Continuing Survey of Food intakes by Individuals, the mean magnesium intake by males age 9 and older was 323 mg/d— far below today's RDA of 420 mg/d. Similarly, for women older than 9, the mean intake was 228 mg/ d—again, significantly below the RDA of 320 mg/d.

Intake decreases significantly in persons age 70 and older—precisely those at highest risk for many of the diseases associated with chronic latent magnesium deficiency. Adolescent and adult women tend to take in suboptimal amounts of dietary magnesium. Certain ethnic groups appear to have lower magnesium intake than the general population. According to the National Health and Nutrition Examination Survey (NHANES III) from 1988 to 1991, magnesium intake is particularly low in non-Hispanic blacks.

Changes in dietary habits and food preparation have shortchanged us with respect to dietary magnesium. A century ago, in the absence of processed foods, the average magnesium intake exceeded 400 mg/d. Vegetarians, who eat mostly fresh foods of plant origin still typically consume large amounts of magnesium. As the nation's eating habits have gone from freshly prepared items made in the home to prepared, processed meals and "fast foods" taken on the run, the magnesium content of the food has plummeted.

Refining and processing of grains and other foodstuffs typically results in loss of 70% or more of the magnesium content (as well as other nutrients). The conversion of wheat into flour results in a loss of 82% of magnesium. Refining rice into polished rice sacrifices 83% of the magnesium. Milling corn into corn starch loses 98% of the magnesium. When soy beans are cooked, they lose 69% of their magnesium. Quick-cooking oatmeal provides only about 15% of the magnesium obtained from the slow-cooking cereal.

The sodium and phosphate found in high amounts in many of today's processed and prepared foods hinder the use of magnesium in the body. A fast-food hamburger for example, packs a double whammy; virtually devoid of magnesium itself, it is extremely high in sodium, which facilitates magnesium loss. In addition, phosphates and polyphosphates bind magnesium in the gut, leading to magnesium malabsorption. Phosphates are found in soft drinks, especially cola beverages (essentially devoid of nutritional value), and polyphosphate preservatives are ubiquitous in baked goods. The estimated average intake of phosphate is probably 2 to 3 times the RDA for a majority of the population—an unfortunate reversal of the situation seen with magnesium that aggravates the problem of chronic latent magnesium deficiency.

All these data point to 2 reasonable conclusions. First the American public consumes less magnesium than necessary for good health. Second, magnesium supplementation, either in the form of oral supplements or specific magnesium-rich foods may be of value to many people, especially patients who have or are at risk for many prevalent chronic diseases.

Chronic latent Mg deficiency

Chronic latent magnesium deficiency is the inadequate intake or retention of magnesium in association with a constellation of diseases (or risk factors for those diseases) in which magnesium deficit is a risk factor or part of the pathophysiology. The diseases and conditions for which risk is increased by chronic but subclinical magnesium deficit include cardiac arrhythmias, coronary artery disease (CAD), diabetes mellitus, hypertension, migraine, osteoporosis, and premenstrual syndrome (Table 2).

Wellness Table 2

Epidemiologic data from numerous clinical and population-based studies have established links between inadequate magnesium intake and elevated risk for cardiovascular diseases. Longitudinal follow-up of more than 8,000 patients for 10 years in the NHANES I Follow-up Study demonstrated inverse relationships between total serum magnesium concentration and risks of coronary heart and vascular disease deaths and hospitalizations. Ascherio and colleagues found that blood pressure tended to be lower in people whose fruit and vegetable intake—and therefore magnesium intake—was high. In the Honolulu Heart Study, the factor most strongly associated with blood pressure control, was high magnesium intake. In the Atherosclerosis Risk in Communities (ARIC) Study, involving more than 15,000 participants, dietary magnesium intake was inversely associated with systolic and diastolic blood pressures.

Lawrence M. Resnick, MD, of Cornell University Medical College, has further outlined the strong link between magnesium and hypertension in a previous issue of The Magnesium Report (Resnick LR. Oral magnesium and hypertension: Research and clinical application. The Magnesium Report. 1999; first quarter). Michael Shechter, MD, MA, of Tel Aviv University, Israel, described his own successful research into the use of oral magnesium to reduce risk of acute myocardial infarction in patients with known CAD (Shechter M. Oral magnesium in coronary artery disease: fresh insight on thrombus inhibition. The Magnesium Report. 1999; August). Ezra A. Amsterdam, M of the University of California, Davis, Medical Center described the potential for event-rate reduction that oral magnesium supplementation holds for patients at risk for cardiac arrhythmias, including patients who have congestive heart failure.

The connection between osteoporosis and magnesium is also becoming stronger. Just last year, a subset analysis of the Framingham Heart Study showed that dietary intake of magnesium {as well as potassium) was directly related to bone mineral density (BMD) and reduced declines in BMD in men and women. A subset analysis of women who participated in the Aberdeen Osteoporosis Screening Program suggested that high intakes of magnesium and other electrolytes in milk and fruit over the long term are associated with higher BMD and may be important to bone health.

The common denominator between magnesium intake and these diseases, as well as diabetes mellitus, migraine, and premenstrual syndrome is chronic latent magnesium deficiency. It is reasonable to suspect chronic latent magnesium deficiency in any patient with cardiovascular disease, diabetes mellitus, migraine, osteoporosis, or premenstrual syndrome, or risk factors for any of these conditions. The approach for the clinician faced with a patient in whom chronic latent magnesium deficiency is suspected is to improve the dietary intake of magnesium and, if necessary, provide oral magnesium supplementation (see Q&A: Magnesium and Wellness). In a subsequent issue of The Magnesium Report, chronic latent magnesium deficiency will be described in greater detail and the practical aspects of the relationship between magnesium intake and the diseases comprising the constellation of chronic latent magnesium deficiency including diabetes, will be discussed.

Wellness Table 3

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