Decoding Magnesium Supplements: What You Actually Need to Know

A Texas Health dietitian explains who really needs magnesium, who doesn’t, and why your pantry may already have you covered.

Your social media feed is probably full of ads for vitamins, wellness shakes and protein powders. Most come with big promises and guarantees. And when a celebrity or influencer is doing the selling, it's even harder to scroll past it.

Magnesium is one of the hottest trends right now. But if you're like most people, you may not be sure what magnesium actually is or what it does in your body. Maybe you've already stopped by the vitamin store to stock up. Is that safe? Do you even need it?

We asked Susan Rodder, MS, RD, LD, a 34-year Texas Health veteran and current registered dietitian at Texas Health Dallas, for her thoughts on magnesium.

"Most people can get all the magnesium they need from food," says Rodder. "If you focus on healthy foods, like those in a Mediterranean diet, and add a few that are higher in magnesium, such as nuts, beans and leafy greens, you'll get there." And unlike supplements, food comes with no side effects.

What is Magnesium? Magnesium Benefits for the Body

Magnesium is a mineral your body needs to stay healthy. Your body can't make it, so it has to come from what you eat and drink.

Rodder likes to compare magnesium to a multi-tool, the kind of pocketknife that folds out into pliers, a blade, scissors and several screwdrivers. Magnesium is a helper, called a cofactor, she explains. It helps the body carry out somewhere between 300 and 600 different chemical reactions.

Here's another way she describes it: if your body's enzymes are a drill, magnesium is the drill bit. The drill can't do its job without it.

According to the National Institutes of Health, magnesium helps your body:

• Keep nerves working properly
• Support heart health by widening blood vessels and improving blood flow
• Build strong bones by activating vitamin D and helping lay down calcium and phosphate
• Use insulin
• Support brain chemicals tied to stress, mood and sleep
• Make energy

That last job is one reason people who are low in magnesium may feel tired. But Rodder is quick to point out that many things can make you tired, including medication side effects, poor sleep, diabetes, heart disease and severe anemia. Feeling worn out doesn't automatically mean you need magnesium.

Skip the Supplement: Magnesium is Already in Your Food

According to the National Health and Nutrition Examination Survey (NHANES), only about half of Americans get enough magnesium from what they eat. Most of the rest of us could get there too, Rodder says, simply by eating more of the foods that are rich in magnesium.

Rodder's list of good sources of magnesium includes:

• Nuts and seeds: almonds, cashews, pumpkin seeds and chia seeds
• Beans and legumes: black beans, kidney beans and lentils
• Dark leafy greens: spinach and kale
• Seafood and dairy: salmon, halibut, milk and yogurt
• Produce and everyday foods: potatoes, bananas, avocados, peanut butter and chicken

Supplements really only help people whose bodies are truly low in magnesium, often because of a health condition, a medicine or a diet that falls short. Doctors call this being deficient.

"The people who truly benefit from a supplement are those who are deficient," says Rodder. "If you're already getting a good amount of magnesium from food, you're probably just wasting your money."

And don't worry about overdoing it at the dinner table. It's very hard to get too much magnesium from food, Rodder says, because food delivers it gently over the course of the day. Supplements, protein powders and electrolyte powders are different. They can deliver a large dose all at once.

Who is Most at Risk for Low Magnesium?

Some groups of people are more likely to run low on magnesium, Rodder says. They include:

• Teenagers
• Adults older than 70
• People with diabetes or heart disease
• Patients living with digestive conditions such as Crohn's disease, ulcerative colitis and celiac disease, which make it harder to absorb nutrients
• Individuals who take certain medicines long term, especially acid reflux medicines and diuretics (water pills)

Signs of Low Magnesium

The most common signs of being low in magnesium are general and easy to miss, Rodder says. The signs and symptoms may include:

• Feeling tired or weak
• Loss of appetite
• Nausea or vomiting
• Muscle cramps, twitching or weakness

Less often, low magnesium can cause a racing or irregular heartbeat. In very rare cases, it can cause seizures.

How Magnesium is Tested

A simple blood test checks magnesium levels. A normal range is 1.7 to 2.2 milligrams per deciliter.

The test is not perfect, though. Rodder explains that the body can pull magnesium from the bones to keep blood levels steady, so a blood test does not always show a true shortage. Doctors regularly check magnesium in patients who take medicines known to lower it.

Navigating Supplements and Prescription Interactions

Rodder warns about something called polypharmacy, which means taking more than five medicines a day. Pills and powders can pile up fast. You might take a magnesium supplement, a multivitamin and an electrolyte powder. Together, they can add up to far more magnesium than you planned or that your body needs. Some supplements also work against each other. Zinc, for example, can block your body from absorbing magnesium.

Antacids can contain magnesium too, and the amounts vary widely. Some have little or none, while others have up to 200 milligrams per dose. Check the label, and ask your doctor if a supplement is okay for you to take.

The most common reasons people take magnesium are as a laxative or to help with sleep. If your doctor approves a supplement, Rodder recommends following his or her advice and:

• Taking no more than about 200 milligrams a day of magnesium supplements.
• Never going over 350 milligrams a day from magnesium supplements. This is the upper safe limit. (Magnesium from food doesn't count toward this number.)
• Taking magnesium at least two hours apart from prescription medicines. Each can keep your body from absorbing the other.

How to Read a Magnesium Label

In supplements, magnesium is always attached to another substance that carries it. The amount of actual magnesium is called elemental magnesium, and it's usually much smaller than the number on the front of the bottle. A bottle that says "500 milligrams" may contain only 100 milligrams of elemental magnesium.

Labels are supposed to list elemental magnesium on the back, but Rodder says many don't. When it's missing, she suggests looking for 50% of the Daily Value according to the U.S. Food and Drug Administration (FDA) nutritional standard. That works out to about 210 milligrams, right at the amount she recommends. The full Daily Value is 420 milligrams.

Choosing the Right Type of Magnesium

The type of magnesium matters too, she says. According to the NIH, different types of magnesium affect the body in different ways:

• Magnesium citrate and magnesium oxide have a laxative effect.
• Magnesium glycinate is gentler on the stomach, has less laxative effect and is often used for sleep.
• Magnesium chloride is well absorbed and used for general magnesium replacement. It can also have a laxative effect.
• Magnesium L-threonate is marketed as able to reach the brain. Studies show minimal benefit, and it's expensive. "Generally speaking, it's not worth it," says Rodder.

Rodder also warns against labels that make big promises or guarantees, like claims that a supplement will “cure your anxiety or guarantee a good night’s sleep.” Those are red flags. Unlike prescription medicines, supplements don’t have to be proven safe and effective before they're sold.

Magnesium for Sleep: Does It Help?

"Not really. A little bit, but not significantly," says Rodder.

Instead, she recommends going back to the basics of good sleep:

• Finish eating three hours before bedtime.
• Avoid caffeine in the late afternoon and evening.
• Turn off screens 60 minutes before bed. Blue light slows your body's natural production of melatonin, the hormone that helps you sleep.
• Keep your bedroom cool and dark.

Signs of Too Much Magnesium

Too much magnesium can cause:

• Diarrhea
• A drop in blood pressure
• Muscle weakness
• Irregular heartbeat
• Trouble breathing

If you notice these symptoms, seek medical care immediately.

"If your magnesium is too low or too high, it can affect the beat of the heart," says Rodder.

Your kidneys play a role here as well. As people age, and as they take more medicines, the kidneys may not filter as well, which affects how the body handles magnesium. If you have kidney problems, talk with your doctor before taking magnesium.

Important: If You Read Nothing Else, Please Read This

Over-the-counter heartburn and acid reflux medicines can lower your magnesium levels when taken for an extended time period. Rodder wants patients to know:

• These medicines, including proton pump inhibitors (PPIs), are meant to be taken for about two to four weeks.
• Many people take them for months or years, often without their doctor knowing.
• Long-term use can cause magnesium levels to drop a lot.
• If you take these medicines regularly, tell your doctor and ask whether your magnesium should be checked.

"People take them for really long periods of time, and that can decrease magnesium absorption," says Rodder.

Bring the Full List of Supplements and Prescriptions to Your Doctor’s Visit

At your annual checkup, bring a list of every medicine and supplement you take, or even the bottles themselves. Many people add supplements on their own without knowing how those products may interact with each other or with their prescription medicines. Some combinations can keep a medicine from working the way it should, and others may not be safe to take together. Doctors call these drug interactions. Bringing the full list helps your doctor identify any problems and stop anything you no longer need.

Rodder says patients are often hesitant to share everything. "Patients are sometimes afraid to tell their doctors what supplements they're taking because they know the doctor will encourage them to cut back," she says.

Her advice is to ask a clear, focused question, such as: "I've read a little about magnesium and sleep. Do you think it would be okay if I tried it to help me sleep at night?"

How a Registered Dietitian Can Help

Registered dietitians are trained nutrition experts. They can sort facts from myths and turn the latest research into eating plans that work in real life.

Texas Health offers nutrition counseling in person or online. Dietitians help people stay healthy and manage conditions such as heart disease, diabetes, digestive problems, kidney disease, weight and food allergies. At a visit, a dietitian may review your eating habits, help you set goals and teach you how to read labels and shop for groceries. The dietitian also sends a report to your doctor.

Learn more about nutrition counseling at Texas Health here.

8 Reminders About Magnesium

• Most people can get all the magnesium they need from food, with no supplement.
• Nuts, seeds, beans, dark leafy greens, fish, yogurt, potatoes, bananas and avocados are all good sources of magnesium.
• Supplements mainly help people who are truly low in magnesium.
• Talk to your doctor before starting a supplement, and keep it to about 200 milligrams a day.
• Check labels for elemental magnesium, and skip products that promise or guarantee results.
• Magnesium does little for sleep. Good sleep habits matter more.
• Long-term use of over-the-counter acid reflux medicines can lower magnesium. Tell your doctor if you take them.
• Bring a full list of medicines and supplements to every checkup so your doctor can check for drug interactions.

Want help deciding if magnesium is right for you?

Texas Health is here to connect you with the right support. With primary care providers and registered dietitians across North Texas, we can help you find the care you need. Find a provider online, or call 1-877-THR-WELL (847-9355).