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Magnesium & Diabetes

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Magnesium is good for diabetics!!

November 2004

The Magnesium-Diabetes Connection Today’s Dietitian By Victoria Shanta-Retelny, RD, LD Vol. 6, No. 11, p. 37

Find out which foods complete the puzzle of this nutrient’s link to diabetes.

In a gallant effort to keep the rising rates of diabetes at bay, nutrition researchers are digging deeper to uncover the role micronutrients play in glucose metabolism. A mineral commanding recent attention is magnesium. Few studies have addressed the association between specific micronutrient components of western diets and diabetes risk.1 “A growing body of evidence,” explains Jerry L. Nadler, MD, division chief of endocrinology and metabolism at the University of Virginia, “suggests that magnesium plays a pivotal role in reducing cardiovascular risk and may be involved in the pathogenesis of diabetes itself.” A combination of recent research findings suggest that magnesium keeps blood sugars from rising too high, thus staving off diabetes.

Experts do not know exactly what the magical mechanism is behind magnesium’s ability to decrease insulin resistance. According to Monika Waelti, PhD, of the Swiss Federal Institute of Technology in Zurich, Switzerland, “Low magnesium intake seems to play a role in the development of diabetes and insulin resistance.” Waelti references three large epidemiological studies, including two Harvard studies—Nurses’ Health Study (NHS) of 85,000 women and Health Professionals Follow-Up Study (HPFS) of 43,000 men, as well as the University of Minnesota’s Iowa Women’s Health Study of 40,000 women—which show “an inverse association between magnesium intake and the development of diabetes.” These studies’ findings revealed that those who ate more magnesium-rich foods, such as whole grains, vegetables, and legumes, were less likely to develop type 2 diabetes.

What Is the Evidence? The data from the NHS and HPFS studies are “robust and significant,” according to Frank Hu, MD, MPH, PhD, associate professor of nutrition and epidemiology at the Harvard School of Public Health. With Hu’s research primarily focused on the role of dietary and lifestyle factors in the development of type 2 diabetes, obesity, and cardiovascular disease, the two large ongoing cohort studies at Harvard, NHS and HPFS, comprise the majority of his research.

“It is a well-established fact that magnesium is a cofactor for insulin action and plays a critical role in insulin sensitivity,” Hu explains. The Harvard research confirmed this principle by showing that increased consumption of magnesium-rich foods in both healthy men and women significantly lowered their risk of type 2 diabetes by enhancing insulin sensitivity. Increasing dietary sources of magnesium appears to be the key. Hu emphasizes, “The research does not suggest supplementation but encourages people to eat a healthy diet, which is high in magnesium-rich foods.”

The Iowa Women’s Health Study found that over the six years of the study, higher consumption of total grains, whole grains, total fiber, cereal fiber, and magnesium were associated with a lower incidence of type 2 diabetes. Those with the highest intake of cereal fiber (7 to 10 grams per day) reduced their risk of developing type 2 diabetes by approximately 30% compared with those with the lowest intake of cereal fiber (2 to 4 grams per day).7 Analyses from the 1989 Total Diet study of the FDA indicated that approximately 45% of dietary magnesium was obtained from vegetables, fruits, grains, and nuts, whereas approximately 29% was obtained from milk, meat, and eggs.8

These findings are crucial since type 2 diabetes is on track to become one of the major global public health challenges of the 21st century.3 The western diet is severely lacking in magnesium because highly processed foods are stripped of this vital nutrient. Since hypomagnesemia is a common feature in patients with type 2 diabetes, the usual question is: What came first, the disease or the deficiency? Although diabetes can induce hypomagnesemia, magnesium deficiency has also been proposed as a risk factor for type 2 diabetes.4 Refined foods generally have the lowest magnesium content. With the increased consumption of refined and/or processed foods, dietary magnesium intake in the United States appears to have decreased over the years.9 For example, the average American is getting only 6 milligrams from white bread, whereas its less consumed, unrefined counterpart, whole grain bread, has more than four times that amount at 26 milligrams per serving.

How Much Magnesium Is Beneficial? The National Institute of Health describes magnesium as a mineral needed by every cell. It is needed for more than 300 biochemical reactions in the body as it helps maintain normal muscle and nerve function and keeps heart rhythm steady and bones strong. It is also involved in energy metabolism and protein synthesis. Only 1% of the magnesium in the body is found in blood. The human body works hard to keep blood levels of magnesium constant.2

With the Daily Value (DV) of magnesium set at 400 milligrams, experts believe Americans do not consume nearly enough. The DV standards have been supported by the National Academy of Sciences and the Institute of Medicine after great deliberation, research, and literature review; an estimated 50% to 85% of the U.S. population is receiving inadequate magnesium intake.5

Nadler points out that many studies have shown that both mean plasma- and intracellular-free magnesium levels are lower in patients with diabetes than in the general population. The American Dietetic Association mandates that serum magnesium levels be measured in diabetes patients who have the following concomitant conditions5:

• acute myocardial infarction;

• calcium deficiency;

• congestive heart failure;

• ethanol abuse;

• ketoacidosis;

• long-term parenteral nutrition;

• long-term use of certain drugs such as diuretics, digoxin, or aminoglycosides;

• potassium deficiency; and

• pregnancy.

In 1992, the American Diabetes Association issued a consensus statement that concluded: “Adequate dietary magnesium intake can generally be achieved by a nutritionally balanced meal plan as recommended by the American Diabetes Association.” It recommended that “…only diabetic patients at high risk of hypomagnesemia should have total serum (blood) magnesium assessed, and such levels should be repeated only if hypomagnesemia can be demonstrated.”2

In Nadler’s clinical practice, all patients with existing diabetes are seen by a dietitian. The magnesium levels are measured, and if subclinical levels are found, Nadler explains, “the first line of therapy used is dietary sources to replenish magnesium stores.” There are exceptions to the rule, such as in people on calorie-restrictive diets, where supplementation is necessary. Nadler emphasizes, “It is even harder to get the recommended daily allowance for magnesium when on a strict weight-loss diet.” Supplementing with wheat germ or leafy greens is a possible remedy mentioned by the Virginia-based endocrinologist.

Magnesium received honorable mention as a food source that can prevent the onset of type 2 diabetes in the June issue of Nutrition Action HealthLetter. The data indicated that women who ate 375 milligrams of magnesium-rich foods daily (compared with 220 milligrams per day) and men who ate 450 milligrams of magnesium-rich foods daily (compared with 270 milligrams per day) lowered their risk of diabetes by roughly 25% and 30%, respectively.6

The expert consensus is that an overall healthy diet is the best prevention for diabetes since that ensures adequate intake of magnesium and other nutrients such as folate, other B-vitamins, and fiber. To meet the DV for magnesium, the most bioavailable sources of the mineral are whole grains, avocados, squash, almonds, fruits, and leafy greens.

Magnesium is also abundant in drinking water, especially “hard” water, which typically has a higher concentration of magnesium salts. A study in Taiwan showed the risk of dying from diabetes to be inversely proportional to the level of magnesium in the drinking water. According to a study in the American Journal of Clinical Nutrition, since 1970, chronic mortality in Taiwan was found to be due to diabetes. The findings revealed that the chronic latent magnesium deficit caused the pathogenesis of diabetes even more so than clinical hypomagnesemia, thus suggesting that dietary magnesium—including from the water supply—is protective against diabetes.5

Why Is Magnesium Vital to Blood Sugar Stabilization? Physiologically speaking, there are reasons that magnesium storage and depletion are important factors, especially in people with diabetes. Magnesium depletion is found in a number of diseases of cardiovascular and neuromuscular function, malabsorption syndromes, diabetes mellitus, renal wasting syndromes, and alcoholism.11

Magnesium depletion in clinical observational studies has been defined by low serum magnesium concentrations as well as a reduction of total and/or ionized magnesium in red blood cells, platelets, lymphocytes, and skeletal muscle.12 One possible cause for the magnesium depletion seen in diabetes is glycosuria-induced renal magnesium wasting.13

Waelti explains, “Magnesium depletion appears to have a negative impact on glucose homeostasis and insulin sensitivity, thus the impairment of insulin sensitivity seems to be related, at least in part, to a defective tyrosine kinase activity of the insulin receptor.” She explains that since there are several enzymes involved in glucose metabolism that require high-energy phosphate bonds, magnesium as a cofactor is required.

As far as magnesium depletion, the Swiss researcher listed major factors for urinary losses of magnesium, such as poor metabolic control, impaired renal reabsorption, and the use of diuretics. Waelti and her colleagues’ research indicates that magnesium absorption is not intrinsically impaired in patients with type 2 diabetes; however, their hypothesis (which has yet to be confirmed) is that “magnesium absorption might be decreased in people with type 2 diabetes due to enteric neuropathy and microvascular disease,” explains Waelti.

Expectant mothers who have diabetes should make sure they have enough magnesium stores. Infants of mothers with type 1 (insulin-dependent) diabetes mellitus are at risk of hypocalcemia and hypomagnesemia, possibly due to magnesium deficiency in the mother.16 Lower intracellular magnesium concentrations have been recently reported in women with gestational diabetes.17 It is not known whether this is a sequellae of the condition or a factor in its causation.18

How Are Magnesium Levels Measured? Magnesium losses are measured with a magnesium tolerance test, which is based on the renal excretion of a parenterally administered magnesium load. It is considered by some to be an accurate means of assessing magnesium status in adults but not in infants and children.14 However, the sensitivity of this method in detecting magnesium depletion may be different between subjects with and without hypomagnesemia. One of the problems in using the magnesium tolerance test is that it requires normal renal handling of magnesium. Urinary magnesium loss (related to conditions such as diabetes or drug or alcohol use) may yield an inappropriate negative test.15 A serum magnesium concentration of less than 0.75 millimoles per liter (1.8 milligrams per deciliter) is thought to indicate magnesium depletion.19

Age may also be a confounding variable for measuring magnesium retention, since older subjects (73 ± 6 years) have been reported to retain significantly more magnesium than younger subjects (33 ± 10 years), despite a comparable mean daily dietary magnesium intake of 5.1 milligrams (0.2 millimoles per kilogram) of body weight.20

Putting Magnesium Into Practice Dietetics practitioners are faced with the continued task of educating patients/clients on the importance of magnesium-rich foods. Whether helping people manage diabetes or prevent its onset, it is essential to stress the importance of getting optimal nutrition from all food groups. Melissa Sujak, RD, CDE, at Northwestern Memorial Hospital Wellness Institute in Chicago knows all too well the importance of emphasizing magnesium in the diet as “these are the foods that increase insulin sensitivity,” she says. With the proliferation of processed foods in the western diet, Sujak is a big advocates emphasizing the utility of magnesium-rich foods. She points to the National Health and Nutrition Examination Survey III (NHANES III) as evidence that the American diet is deficient in three food groups that are the highest in magnesium: whole grains, fruits, and vegetables.

The NHANES III study demonstrated ethnic differences in magnesium intake. In that report, non-Hispanic black subjects were found to consume less than either non-Hispanic white or Hispanic subjects.10 When educating patients, “let’s be proactive, not reactive,” Sujak states.

Everyone can benefit from magnesium-rich foods—not only for diabetes prevention but also for a decrease in risk factors. Waelti says, “A diet rich in magnesium would benefit everyone, especially people with risk factors for type 2 diabetes, such as obesity, hypertension, elevated blood lipid levels, or a family history of diabetes.”

— Victoria Shanta-Retelny, RD, LD, is a practicing dietitian at Northwestern Memorial Wellness Institute in Chicago, a freelance food and nutrition writer, and a culinary spokesperson.

References for this article are available by e-mailing

Food Sources of Magnesium Tofu, firm, 1/2 cup 118mg Chili with beans, 1 cup 115mg Wheat germ, toasted, 1/4 cup 90mg Halibut, baked, 3 ounces 78mg Swiss Chard, cooked, 1 cup 75mg Peanut, roasted, 1/4 cup 67mg Baked potato with skin, 1 medium 55mg Spinach, fresh, 1 cup 44mg

— Source: USDA: Composition of Foods. USDA Handbook No. 8 Series. Washington, D.C., ARS, USDA, 1976-1986.


Magnesium & Diabetes Magnesium is good for diabetics!!