Magnesium for Heart Health: How to Best Resolve a Gap?

Inside: Some people may not think of magnesium for heart health or know how to increase magnesium. For diets low on magnesium, boost foods like whole grains to close a gap.

 

At the grocery store one day, I saw several women huddled in lively discussion in the supplement aisle. One of them was looking for magnesium. Her friend and a few other shoppers gathered to debate confusing questions. How much was enough? Would her multivitamin provide a sufficient amount? Did she need to consider interactions with other supplements and medications? And what is magnesium for, anyway?

This is an example of how a simple question can become overwhelming.

 

Headlines abound warning that diets today often lack enough magnesium.

But most people are left with a lot of uncertainty about whether they really need more magnesium… and if so, how to get it.

According to the latest national dietary data, more than half of American adults eat a diet that doesn’t supply recommended amounts of magnesium. That’s concerning, since research shows that magnesium may support better blood pressure control, bone health, and insulin sensitivity. With implications for risk of type 2 diabetes, heart disease and some cancers, attention to the gap between magnesium recommendations and what eating habits provide is well worth considering.

The scientific evidence is not clear-cut.

But it does support a few smart tweaks in food choices that can fill a magnesium gap for most people… and help fill several other nutrient gaps at the same time.

 

Magnesium: Overlooked Piece of the Puzzle in a Healthy Diet?

Magnesium plays many roles in maintaining health. And amounts needed to fulfill these roles were not the basis for setting recommendations for dietary magnesium.

Let’s review the research on magnesium consumption and some key aspects of health.

Magnesium for Heart Health: How Much Benefit?

Magnesium influences multiple risk factors for cardiovascular disease. So it may be no surprise that an analysis of 14 prospective cohort studies in large populations linked higher magnesium in the diet with lower risk of stroke and heart failure.

But overall, studies like this do not show a consistent link to cardiovascular disease development or deaths. That’s true whether comparing highest versus lowest intake of magnesium, or with analysis based on each additional 100 mg/day consumed.

 

Don’t write off the potential for protection, however. A closer look at these observational studies shows that there are large variations in their findings – what researchers refer to as high heterogeneity.

• Although higher dietary or total magnesium consumption showed an association with lower CVD deaths that was not statistically significant (meaning it could have occurred by chance), there was an association among people classified as having overweight or obesity.
• And although these studies adjusted for major CVD factors, most did not adjust for intake of other nutrients that could be involved in heart disease. In studies that controlled for differences in calories as they looked for associations, higher magnesium intake was associated with fewer CVD deaths.

Magnesium in the Body: How It Protects Cardiometabolic Health

High blood pressure is more likely to develop in people whose diets are low in magnesium. An analysis combining multiple prospective cohort studies found that people with diets providing magnesium similar to the current RDAs were less likely to develop hypertension than those consuming less than 200 mg/day (the bottom tenth percentile of current US adult intake, and well below estimated average requirements). The association with magnesium showed a linear pattern, with each 100 mg/day of dietary magnesium consistently associated with a 5% lower risk of hypertension.

Randomized controlled trials using magnesium supplements to maintain specific level of magnesium intake confirm that magnesium can play a role in reducing blood pressure. But one review separately analyzed effects in people with uncontrolled hypertension, controlled hypertension and normal blood pressure. It concluded that for people consuming enough magnesium or whose blood pressure is at a healthy level, adding more magnesium does not affect blood pressure.

Endothelial dysfunction and artery stiffness affect not only blood pressure, but other aspects of cardiovascular health, too. Food choices can influence vascular health and artery aging – and part of that includes providing adequate magnesium.

Magnesium modulates constriction of blood vessels triggered by vasoactive peptides and hormones. It influences production of vasodilators like nitric oxide within blood vessels and improves blood vessel relaxation responses. Magnesium helps avoid loss of elasticity and increased stiffness in blood vessel walls by regulating turnover of collagen and elastin. And through its role regulating active transport of calcium and potassium across cell membranes, magnesium influences heart and muscle cell contractility.

Multiple randomized controlled trials with magnesium supplements studied whether increasing magnesium intake could affect measures of blood vessel health. Results of these trials differ widely, and many show no significant across the board improvement by increasing magnesium. But among studies that lasted at least six months, or among people either over age 50 or with a BMI categorized as overweight or obese, increasing magnesium has shown improvement in some measures of vascular health.

Inflammation, another factor in development of many chronic diseases, may be related in part to magnesium. In a combined analysis of several studies, people whose diets provided magnesium that met current RDAs (400 mg/day or more) were less likely to have elevated levels of a marker of inflammation (CRP) compared to people with lowest intake. Those with lowest consumption got less than about 200 mg/day, well below estimated average requirements.

• Oxidative stress increases when the body lacks adequate magnesium. That makes sense, since lack of magnesium increases generation of free radicals, decreases expression or activity of antioxidant enzymes (many of which depend on magnesium as a cofactor), and decreases synthesis and release of nitric oxide in the endothelium (the layer lining the inside of arteries).
• Randomized controlled trials using magnesium supplements ranging from 250 to 500 mg/day have shown decreases in CRP if baseline CRP level was elevated (≥3.0 mg/L) and blood levels of magnesium were low. In trials involving subjects with healthy baseline levels of CRP and magnesium, increasing intake with magnesium supplements generally shows no effect.

Insulin resistance – the starting point of type 2 diabetes – is more common in people with low magnesium intake. Magnesium affects insulin secretion, release and signaling, as well as glucose transportation across cell membranes.

• Metabolic syndrome is a collection of risk factors for heart disease, such as high blood pressure and high triglycerides, that is also linked to a five-fold increase in risk of diabetes. Insulin resistance is a key factor driving development of this syndrome.
• People with highest magnesium in their diets were almost 30% less likely to develop metabolic syndrome during an average 10-year follow-up compared to people with lowest intake. Those low levels were well below estimated average requirements. But that’s typical of many US adults according to recent dietary surveys.
• Higher magnesium intake has been linked with less metabolic syndrome in multiple observational studies. Many of these, however, are cross-sectional or case-control studies, which are more prone to bias and need to be interpreted cautiously. These studies are often unable to separate the influence of magnesium from other nutrients and phytochemicals in high-magnesium diets, and there is wide variation in results of individual studies.
• Metabolically Obese Normal Weight (MONW) refers to metabolic abnormalities (such as insulin resistance and inflammation) typically seen in people who have weight classified as overweight or obesity…but occurring in people of normal body weight. Researchers are hunting for ways to identify these conditions. Limited evidence suggests that magnesium intake may be involved.

 

Supplements can be helpful to increase magnesium intake. But they may not produce the same health benefits as changes in eating habits, since magnesium-rich foods provide other protective nutrients and plant compounds, too. Share on X

 

How Big is the Magnesium Gap? Making Sense of the Evidence

To accurately interpret studies about magnesium and health, you need to know how researchers determined who was lacking magnesium and who was getting enough. That includes considering the accuracy of available assessments and the basis for recommended magnesium intake.

How to Test Magnesium Level: Is Serum Magnesium Best?

In research and in clinical care, a blood test (serum magnesium) is the most common way of checking whether someone is low on magnesium (and to check for excessive levels). Normal serum magnesium concentrations range between 0.75 and 0.95 mmol/L (1.82–2.30 mg/dL). Levels chronically below this range are associated with increased cardiovascular disease incidence and deaths. Severe depletion can lead to heart arrythmias.

Yet serum magnesium represents only about 1% of the magnesium in the body. Bones hold about 50% to 60% of the body’s magnesium, and most of the rest is in muscle and other soft tissues. Before you assume that serum magnesium within the reference “normal” range clears up concern about magnesium, consider what blood tests for magnesium do not show….

• Normal serum magnesium does not necessarily mean that total body magnesium stores are at healthy levels. Blood levels could be maintained by moving magnesium to the blood from bone and soft tissues.
• Serum magnesium does not provide a reliable marker of magnesium consumption. Studies show only weak correlations with magnesium intake. This could reflect the challenges of accurately assessing magnesium intake. But could also occur as body mechanisms to maintain homeostasis can keep serum magnesium in the normal range despite intake that is low or that is well above needs.
• The reference range for serum magnesium was formulated based on the levels seen in a normal population – not on research relating serum magnesium levels to clinical outcomes. Even while maintaining normal serum magnesium levels for years, researchers say that someone could have a subclinical deficiency that evidence now ties to increased risk of inflammation and cardiovascular disease.

There are other methods to assess magnesium status, but most are rarely used in clinical practice and are often too invasive, expensive, or impractical even for use in research studies.

How Much Magnesium? Your Guide to the Controversies

The average American adult’s diet provides about 50-75 milligrams less than the Recommended Dietary Allowance (RDA) for magnesium. RDAs are levels set to meet the needs of virtually all healthy people, so not everyone needs to meet that target. [The current RDA for magnesium is 310-320 milligrams (mg) for adult women, and 400-420 mg for adult men.]

However, half of US adults get less than even the Estimated Average Requirement (EAR). That’s the guidepost intended for assessing intake of groups of people. So this suggests that quite a few people are either low or cutting it close for magnesium. People with lower income levels, adolescents, and adults over age 70 are particularly likely to have diets providing less than the EAR. [For women over age 30, the current EAR for magnesium is 265 mg, and for men over age 30, it’s 350 mg per day.]

Controversies over how to identify people who aren’t getting enough magnesium don’t end with challenges of interpreting blood and urine tests. The EARs and RDAs we use to assess magnesium consumption also pose challenges. These standards were set in 1997 based on a small number of balance studies from the 1980s and ‘90s, each including no more than a dozen people.

• The EARs (and thus the RDAs that are based on them) may be too low a target for many US adults. Magnesium needs increase as body weight increases. From creation of the 1997 recommendation to 2011-2014, average weight reportedly increased 17% in men and 25% in women. And it’s increased even more since then. Based on that increase, magnesium scientist Andrea Rosanoff, PhD, proposes that the EAR is too low. For example, she recommends EARs of 409 mg/day for men over 30, and 332 mg/day for women over 30.
  – And that’s just the beginning. Rosanoff advises that the 10% variance in requirements added to magnesium EARs to create the RDAs is too low. Depending on which variance adjustment was used with the increased EARs, a 10%, 20% or 30% adjustment would bring magnesium RDAs to 491, 573, or 654 mg/day for men over age 30. RDAs for women over 30 would increase to 398, 465, or 531 mg/day.
• These proposed increases in recommended magnesium intake, however, still rely on the original balance study data. Balance studies over the past two decades show that magnesium excretion drops dramatically with low magnesium consumption. Based on these studies, USDA research nutritionist Forrest Nielsen, PhD, proposes that the EAR is too high. – He proposes 175 mg/day for a 70-kg (154-pound) healthy individual. And using a larger adjustment as proposed by Rosanoff to account for individual variation, he proposes an RDA of 250 mg/day for that 154-pound healthy adult. The EAR and RDA figures should increase or decrease based on body weight, he notes.

These proposed adjustments to the guideposts we use to estimate whether someone is likely to be consuming enough magnesium provide a large range for judgement. In addition to weight, other factors could also indicate someone likely to have higher or lower magnesium needs.

Individual differences could make some people benefit from higher magnesium consumption than other people. (And people with reduced kidney function need to be cautious about excessive intake.) Share on X

Who May Need More Magnesium?

People who excrete more magnesium in their urine or who don’t absorb it efficiently from the intestinal tract need to consume more to meet body needs.

• Increased magnesium urinary losses can occur in people with uncontrolled diabetes or elevated blood sugars that lead to increased urine output, people who chronically abuse alcohol, and many older people.
• Reduced magnesium absorption from the gut can occur in people with chronic diarrhea related to celiac disease, inflammatory bowel disease, or other conditions, as well as in those who have had intestinal bypass surgery.
• Medications can increase magnesium losses. For example, loop diuretics and thiazide diuretics, increase urinary excretion. [Potassium-sparing diuretics don’t increase excretion – they reduce it.] The epidermal growth factor receptor inhibitor called cetuximab used in cancer treatment also increases urinary magnesium losses in many people, as does cisplatin. Proton pump inhibitors (PPI) can reduce absorption of magnesium from the intestine. The FDA advises healthcare professionals to consider checking patients’ serum magnesium before and periodically during long-term PPI treatment. Meanwhile, despite concern over decreased absorption, gastroenterological best practices review advises that long-term PPI users should not routinely raise magnesium intake above RDA level before discussion with their healthcare provider.

How Much is Too Much Magnesium?

The Tolerable Upper Limit (TUL) set as part of the Institute of Medicine DRIs applies only to supplemental magnesium, not to magnesium intake from food. The TUL, or maximum amount likely to pose no adverse health effects, is 350 mg/day for all adolescents and adults.

• The adverse effect that is the basis for the TUL is mild, reversible diarrhea. Pharmacologic use of magnesium is well known to produce osmotic diarrhea. But magnesium consumed in food (natural or from fortification) is absorbed more efficiently, and the presence of food in the gut likely counteracts the osmotic effect of magnesium compounds. Some people seem to be especially sensitive to this effect of magnesium supplementation, whereas others may more easily tolerate higher amounts. High intake of magnesium from foods does not promote diarrhea.
• People with impaired renal function can develop elevated blood levels of magnesium from supplements, and especially with excessive intake of magnesium from sources such as antacids or intravenous magnesium. Elevated blood levels can lead to lethargy and abnormal heart rhythms, and when extremely high, can even cause cardiac arrest. Normally, however, the kidneys maintain normal blood levels of magnesium across a wide range of magnesium intake by adjusting amounts excreted in the urine. According to the Institute of Medicine report, magnesium supplements rarely lead to symptomatic hypermagnesemia in people with normal renal function.

The DASH diet, a dietary pattern shown in multiple research studies to reduce high blood pressure, provides 500 mg/day of magnesium (at the 2000 calorie level). In trials on hypertension, although they did not always reduce blood pressure, even magnesium supplements over 500 mg/day reportedly produced no serious adverse effects.

How Much Magnesium to Close the Gap?

Good news: for many people, the gap between what’s provided by eating habits and what’s recommended can be remedied with a few adjustments in food choices.

• For the average American adult, boosting magnesium by 50 mg/day (for women) or 100 mg/day (for men) would allow them to meet the RDA.
• Even for people in the bottom 10% of US adult consumption, women who increase magnesium intake by 100 mg/day, and men who increase it by 150 mg/day, would be enough to bring their diets at least to the minimum standard of the EAR.

 

As noted above, although the current EAR is 255-265 mg/day for women and 330-350 mg/day for men, healthy targets could be higher.

• More could especially be better for people with overweight or obesity; or increased urinary losses of magnesium due to uncontrolled blood sugars, medications, or age.
• People whose diets are low in magnesium and already have health problems such as type 2 diabetes, uncontrolled hypertension, or oxidative stress may need a larger increase in magnesium to see an improvement than those who are low on magnesium and at early stages of cardiometabolic dysfunction.
• But for many aspects of health, increasing low or typical US magnesium intake by 100 to 200 mg/day could help improve elevated markers of inflammation, metabolic syndrome, and uncontrolled high blood pressure.

These increases in magnesium consumption are within reach by making a few dietary tweaks each day.

 

With a few adjustments in eating habits, people with average or below average magnesium intake could increase amounts enough to improve elevated markers of inflammation, metabolic syndrome, or uncontrolled high blood pressure. Share on X

How to Increase Magnesium in Your Diet: A Smart Strategy

Magnesium is not a solo act. In all the ways it supports health, magnesium works in partnership with other nutrients. Adding more may not bring desired results if your eating habits are also lacking in other nutrients.

When eating habits are low on magnesium, that’s likely not the only thing lacking. The gap in magnesium between what we eat and what is healthful often signals a diet that relies on too many highly processed foods.

Focus first on filling the gap. To see if raising magnesium even a little more could help reach biomarkers of health, you could likely add an extra 100 mg with a basic multivitamin or fortified cereal. But even a multivitamin doesn’t provide the fiber and the thousands of natural plant compounds (“phytochemicals”) you get by boosting a variety of magnesium-rich foods in everyday eating habits.

Dietary Sources of Magnesium in a Healthy Eating Pattern

The good news is that simple shifts in basic food choices can add extra magnesium that may be missing. Two or three daily dietary tweaks like those listed below could boost magnesium by 100 to 150 mg/day.

 

Dark Green Vegetables

• Choose dark green vegetables often. All vegetables are healthy choices, but some (like cooked green beans, with 15 mg in a three-quarter cup portion) deliver a smaller magnesium bump. Spinach and Swiss chard are among the highest (112-120 mg in three-quarters of a cup cooked). Collards, kale and other greens all add a boost.
• Instead of a cup of iceberg lettuce (4 mg), have spinach salad (24 mg).
• Sauté spinach with garlic and add it to the top of a pizza, whether homemade or takeout. Fabulous!
• Add green leafy vegetables like spinach to soups, stews, pasta sauce and casseroles, whether you’re cooking from scratch or just bringing a commercial version up a few notches.

Tip: Keep a stash of frozen spinach or other greens on hand, especially through the fall and winter. Frozen versions are as high in magnesium as fresh, and bags in the freezer make it easy to take whatever amount you want to add to what you’ve got cooking.

Bonus: Dark green vegetables also supply vitamin C and beta-carotene, which seem to help reduce risk of chronic diseases. Unfortunately, these vegetables fall short of amounts recommended in the Dietary Guidelines for Americans in diets of about 80 percent of Americans.

 

Whole Grains

• Instead of a refined breakfast cereal with 3 to 8 mg, have oatmeal, shredded wheat, or other whole grain cereal with 60 to 65 mg.
• Switch from a sandwich with two slices of white bread (15 mg) to whole wheat bread (42 to 48 mg).
• Swap a white bread pita (7 to 15 mg in half a 6-inch piece) for a more nutrient-dense whole wheat pita (over 40 mg in the same size).
• Replace white rice (about 20 mg per cup cooked) with brown rice (86 mg per cup). Add variety by experimenting with other whole grains, like quinoa, bulgur, and whole grain sorghum (60 to 120 mg or more per cup).
• Instead of breadcrumbs (6 mg in two tablespoons), sprinkle toasted wheat germ (45 mg) on casseroles, and top yogurt or cereal with it, too.

Tip: Buy plain, unseasoned whole grains like brown rice and quinoa. You’ll usually save money, you’ll avoid the hidden load of sodium, and you’ll have the flexibility to add the herbs and other seasonings that you want in the dish. (Even if you add a pinch of salt, sodium will be far lower than what you get in most “seasoned” grains.)

Bonus: As you replace refined grains with whole grains, you get more naturally-occurring phytocompounds and dietary fiber that support antioxidant, anti-inflammatory defenses. The fiber in some whole grains seems to serve as a prebiotic, nurturing growth of healthy bacteria in the gut that research suggests may support wide-ranging aspects of health. Whole grains lower risk of colorectal cancer.

 

Legumes (Dried beans and peas, lentils, soyfoods)

• Replace some or all of the ground beef or beef cubes in a soup or stir-fry (12-14 mg in two ounces) with tofu chunks (73 mg in a half-cup).
• Add dried beans (black, kidney, garbanzo) to salads and mixed dishes for an easy way to add 20 to 45 mg per half-cup.
• Pretzels (15-20 mg in 10 twists) are low in saturated fat. But choose edamame or roasted chickpeas for a more filling snack with more nutrients (35 to 40 mg in each half-cup). Or munch on soy nuts (62 mg in each quarter-cup).

Tip: It’s quick and easy to add beans to whatever you’re making when you use canned beans. Look for beans labeled No Added Salt. Otherwise, drain and rinse to remove about 40% of the sodium. Dried lentils are another easy choice – they don’t need soaking and cook in a flash.

Bonus: Dried beans, peas and lentils are among our best sources of dietary fiber, including types that seem to support a healthy microbiota. All legumes are also high in folate, a vitamin that supports healthy DNA.

 

Nuts and Seeds

• Instead of snacking on crackers, have a small handful of nuts or seeds. Even though whole grain crackers provide more magnesium than refined grain crackers (4 to 8 mg), a scant handful of nuts (a quarter-cup) gives you 40 to nearly 100 mg. (Just watch the portion so calories don’t get out of control.)
• Forget the croutons (4 mg) or crunchy chow mein noodles (7 mg) on salads. Instead, add crunch with a quarter-cup of nuts or sunflower seed kernels (43 to 96 mg).
• Top cooked vegetables, pasta or grains with nuts. Toast them for a minute and the flavor is even more amazing.
• Add nuts to oatmeal for a higher-protein option that most people find carries them longer through the morning.

Tip: Top cooked vegetables, pasta, or grains with nuts. Toast them for a minute and the flavor is even more amazing.

Bonus: Nuts and seeds are top sources of polyunsaturated and monounsaturated fatty acids, that when replacing saturated fat can reduce LDL cholesterol. And in people with elevated blood pressure, the OmniHeart trial showed that a DASH diet with higher amounts of unsaturated fat is even more effective at reducing blood pressure and 10-year heart disease risk.

 

Other Healthy Swaps

• Fish instead of red meat or chicken typically provides about twice as much magnesium in the same size portion. Including it a few times per week for its omega-3 fatty acids that support heart health can have multiple benefits.
• Winter squash (such as acorn and butternut) also helps boost magnesium, with 30 to 60 mg per cup cooked.
• Tomato-vegetable juice (60 mg in an eight-ounce glass) or tomato juice (25 to 30 mg) can be a tasty alternative if you’re trying to cut back on alcoholic cocktails or sugar-laden soft drinks. Choose low-sodium types. My favorite is V8 Low Sodium, Spicy Hot!
• Dark chocolate (50 mg in a one-ounce piece) can be a pleasant nibble. It’s got more than double the magnesium of the same calorie load in chocolate ice cream or chocolate chip cookies. And the polyphenol compounds in cocoa and dark chocolate seem to support vascular health. But calories can add up quickly. You’ll be surprised at how satisfying a little can be if you eat the chocolate slowly and savor every bite.

 

When I hear grocery store discussions – like the one debating whys and hows of adding a magnesium supplement – I hardly ever jump in. I hope that the woman will ask a registered dietitian nutritionist to help evaluate whether she’s likely getting enough. If she’s among the many people for whom more may be better, she could start with swaps that add foods rich in magnesium and other health protectors before starting conversations about adding a supplement.