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
TDeditor@gvpub.com.
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.
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