Have you noticed the buzz around magnesium deficiency, and supplementation, of late? Do a quick Google search and you’re bound to be overwhelmed by the plethora of information on offer.

But, how accurate is it? I think you’d be surprised. Read on.

No doubt, it’s a mineral vital to our overall functioning and wellbeing. It is the fourth most abundant mineral in the body and is involved in over 300 enzymatic processes, including the regulation of nerve and muscle function, blood pressure, and blood sugar levels. It’s also involved in the production of bone and protein. (1)

With so many functions within the human body, it plays a key role in the prevention, and treatment, of many diseases. (1)

Why now, though, so much interest in this particular mineral?

Well, for a start, it could be because it seems we’re no longer getting enough of it from what we eat and drink. Dietary surveys in the U.S. are consistently revealing that our daily magnesium intakes are lower than the recommended levels (set at 255–350 mg, depending on gender and age group)(1).

The National Health and Nutrition Examination Survey (NHANES) studies the health and nutritional status of adults, and children, in the U.S. About 5,000 people take part, each year, across each demographic. The 2005-2006 NHANES survey found that Americans, of all ages, had lower than recommended dietary magnesium intake. In particular, men aged 71 years and older and, adolescent females (2).

Ok, it’s beginning to sound more concerning.

On top of our low’ish dietary intakes overall, it seems dietary magnesium intake, in the U.S., has been on the decline over the last 100 years, from about 500 mg/day to 175–225 mg/day. The increasing use of fertilizers and processed foods are the likely culprits. (1)

Possibly, this now has you wondering whether you take in enough of the mineral through your diet. Maybe you’re starting to worry about whether you may be magnesium deficient…

There are many articles on the internet advocating that we take a daily magnesium supplement for good health. But would a magnesium supplement be of benefit to you? And if so, in what way(s)?

Let’s take a look…

What is Magnesium Deficiency?

The first point to make here is it’s not easy to accurately measure our magnesium status. The simple fact is that most of it is stored inside our bone (50% to 60%) and most of the rest is in our soft tissue. (1)

The most commonly used method is measurement of blood serum magnesium levels, even though this tells us little about our total body levels of the mineral (3). Less than 1% of total magnesium is in blood serum, and these levels are kept under tight control, mainly by the kidneys. (1)

There are some other ways it could be checked, including measuring magnesium levels in the saliva and urine. However, there really is no gold standard when it comes to measuring magnesium deficiency (4).

Here’s the crazy part…

No current data on magnesium status in the US is available. The most recent data of this kind, determined by NHANES, is from 1974! (5)

NHANES look at dietary magnesium, and they think that in general, it’s a bit low. But in terms of actual magnesium deficiency, there is no data at all!

As you’ll learn below, there is a big difference between having a diet that’s a bit low in magnesium (which may never effect you) and having a real magnesium deficiency.

So, then, how can one even find out if they have a magnesium deficiency to begin with? Well, the usual proxy for gauging magnesium status is determining dietary intake of the mineral, and whether it meets the recommended guidelines set for that country, so that’s where we start.

Yep, that would mean paying attention to what you consume for a while and getting a general idea of whether the recommended intakes are being met, as a way to figure out whether low magnesium intake may be a problem for you.

But it’s important to note that even if you don’t have enough of it through your diet, in the short term, it’s not really an issue for most. (1)

Symptomatic magnesium deficiency as a result of low dietary intake, in otherwise healthy people, is uncommon. Why you ask? Our kidneys do a great job at keeping our magnesium levels in balance by adjusting the amount excreted in the urine, as required. For instance, when magnesium status in the body is low, urinary excretion of the mineral is reduced (1).

Long-term dietary intake of the mineral, below recommended levels, is a different story. Reduced absorption from the gut, or very large losses of magnesium due to certain health conditions, chronic alcoholism, and/or the use of certain medications, can lead to a symptomatic magnesium deficiency. (1,5)

The groups most at risk of magnesium deficiency, therefore, are: people with gastrointestinal disease, people with type-2 diabetes, people with alcohol dependence, and older adults.

Bottom Line: Magnesium dietary intake is most commonly used to gauge a person’s magnesium status, and to identify a potential deficiency, by comparing it to the recommended levels.

How Do You Know If You’re Magnesium Deficient?

In the short term, you’re not going to know whether you’re getting enough magnesium or not. (Unless, say, you added up the magnesium content of everything you ate in a week – there are some good apps. that could help with this). There’s really no “symptom” you can have, that would let you know, with any confidence, that you’re developing a magnesium deficiency. In fact, it’s worth being cautious of any website that suggests otherwise.

If you had a lowered magnesium intake for a longer period of time, however, certain signs of a deficiency might show up. These could include loss of appetite, nausea, vomiting, fatigue, and weakness (1,5).

If you had any of those, you’d be better off seeing your doctor first, rather than buying a magnesium supplement!

Bottom Line: It’s quite hard to tell due to the difficulty in measuring magnesium levels, but you might have a magnesium deficiency if you’re regularly experiencing nausea, and vomiting, among other non-specific symptoms.


There are websites that provide frustratingly misleading information in this area.  I honestly don’t know where to start.

First, one alarmingly states ‘approximately 80% of people have low magnesium levels and chances are that you are one of them’!

Um – The most recent US-data on magnesium levels is from 1974 – there is no current data.

I suspect what the author was trying to convey is the low level of dietary intake of magnesium in the US, rather than low magnesium levels in the body per se. In most healthy people, the former rarely leads to the latter. (1) I have found this confused and misleading point on several websites that I’ve researched. It would, understandably, have many people running for the supplement shelves of their local grocery store.

I found the title of the piece (which I refuse to link to lest it be seen as endorsing their content) quite alarmist also – “9 signs you have magnesium deficiency…”. It later corrects for this, by adding the all important “may” have. The symptoms listed are not exclusive to a magnesium deficiency and there is a real risk of a false diagnosis.

Then, there are the listed “symptoms” themselves. Osteoporosis, and Type 2 diabetes to be possible “symptoms” of a magnesium deficiency? They are actual conditions!! A symptom is “a physical or mental feature that is regarded as indicating a condition of disease”.

Need I write any more on this one?

There are more of these too. Another article title starts “Why we’re all deficient in magnesium..”. I couldn’t help but to burst out laughing when I started to actually read the article, “Signs of magnesium deficiency are everywhere in the United States… Just about every single person you come into contact with .. are suffering in some way from this nationwide deficiency. Including you!”

Forgive me; I just couldn’t take this one seriously anymore.

What Are Magnesium Supplements?


You’ll find magnesium bound to other molecules in supplements, typically salts, known as chelations. This stabilises the magnesium when in the pill and prevents cross-reaction with other minerals.

No doubt you’ve come across magnesium supplements in a variety of forms, depending on what they’re bound to. Here’s just a short list: Magnesium Oxide/Oxalate, Magnesium Citrate, Magnesium Glycinate, Magnesium Chloride, and Magnesium Aspartate.

I’ll give you a heads-up below on which are the better ones.

Also, the ‘Supplement Facts’ panel on a dietary supplement label gives the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound.

How Effective Are Magnesium Supplements?

Do magnesium supplements actually increase your magnesium levels?

This comes down, in part, to the form of magnesium supplement you take. The absorption of magnesium from different kinds of magnesium supplements varies – it’s referred to as bioavailability.

Good ones? The forms that dissolve well in liquid are the ones that are more completely absorbed in the gut (6). You could potentially test this out for yourself, just with a glass of water or juice! Small studies have found that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely (6,7).

Magnesium citrate is the most commonly used form of magnesium supplementation, partly due to its low cost. Its bioavailability is around 25-30%. (7,8)

Not so good ones? Magnesium oxide, one of the most common forms found in magnesium supplements due to its high magnesium content per weight, is actually the least bioavailable (around 4-5%). (9) It may be used as a filler in supplements and can indicate that the supplier is cutting costs. Magnesium sulphate is also poorly absorbed (6,7).

Interestingly, in a study using data from the NHANES 2003-2006 survey, the average intake of magnesium from food alone was higher among users of dietary supplements (350 mg for men and 267 mg for women, equal to or slightly exceeding their recommended levels), than among non-users of supplements (268 mg for men, 234 mg for women). (10).

The funny thing here is – when supplements were included, the average total intake of magnesium was well-above recommended levels (449 mg for men, 387 mg for women). (10)

This would suggest that people most likely to use supplements have a better diet overall and are less likely to need them in the first place. How ironic.

Absorption of magnesium is also affected by other factors.

For instance, intestinal absorption of magnesium is dependent mainly on your current magnesium levels. The lower the magnesium level in the body, the more of the mineral is absorbed by the gut. In essence, magnesium absorption is higher when intake is low and vice versa. (1) Too much zinc can also affect magnesium absorption.

Bottom Line: The effectiveness of magnesium supplements depends partly on your current magnesium status, and, partly on how well absorbed that form of magnesium supplement is. In the average healthy person, they contribute very little, if anything.

And if they do, so what?

So, for most of us with a fairly healthy diet, the extra magnesium from a supplement may not even be absorbed, or may be mostly or entirely removed in the urine, in order to maintain the magnesium balance in the body.

It would be more of a benefit to those who have poor diets over the longer term, or who fall under any of the at-risk categories mentioned above. Long-term low levels of magnesium can increase the risk of illness over time and should be addressed with guidance from a doctor.

Efficacy for various conditions

Are Magnesium Supplements Helpful For Constipation?

We have to be careful in our wording here. There are forms of magnesium that have a laxative effect and are, therefore, a primary ingredient in some laxative medications (11).

The forms most commonly used for this are Magnesium Hydroxide (known as Milk of Magnesia) (12), and Magnesium Oxide. The former may have antacid effects, and the latter is poorly absorbed by the body, so neither of them is suited for nutritional supplementation.

Of course, a typical side-effect of excess magnesium through supplements is diarrhoea.

Bottom Line: Magnesium supplements, per se, are not used to alleviate constipation. Magnesium, in certain forms, is effective as a laxative medication.

Are They Helpful For Sleep?

Magnesium seems to have some role in sleep as a result of sedative-like actions, though there have only been two research studies in humans to assess this, at this time. In both cases, the study subjects had poor sleep quality to begin with.

In a study on 12 healthy elderly persons, magnesium supplementation over twenty days led to an increase in slow-wave sleep and reduced sleeping cortisol (“stress hormone”) levels, which helped to normalize age-related changes in sleep patterns. (13)

In a separate study, benefits to sleep were found in persons aged 59(+/-8) years who consumed less than the recommended levels of magnesium through their diets. A 320mg magnesium citrate supplement over seven weeks improved sleep quality. (14)

Bottom Line: Though an improvement in sleep quality has been found in people with poor sleep quality, there have been no research studies that assess the benefit of magnesium supplements in people with normal sleep function.

Are They Helpful For Weight Loss?

There have been four human studies investigated the effect of magnesium on weight. They have consistently found a lack of evidence to support a role for magnesium in affecting a person’s body weight.

In general, there is no per se link between magnesium levels and body fat. However, reduced magnesium levels correlate with disease states (such as metabolic syndrome) and those disease states are associated with higher body fat. (15)

In this way, magnesium levels may be thought of as a biomarker for the state of obesity, rather than a contributing factor. (16)

Bottom Line: There is no evidence that magnesium plays a role in weight loss.

Are They Helpful For Leg Cramps?

Magnesium supplementation for the purpose of reducing leg cramps has mixed evidence. Even the evidence suggesting it is useful, is quite low-powered and likely not to be clinically relevant.

With pregnancy-related cramping, a common phenomenon during pregnancy, the evidence is mixed. It appears to be more effective than placebo (a dummy tablet – which, in itself, has been found to be beneficial) but the degree to which it is, is not really significant. In a double-blind clinical trial, with only 38 subjects, 360mg Magnesium was unable to exert a significant reduction in pregnancy-related cramping. (16)

The same appears to apply to night cramps. There appears to be benefit to both placebo and magnesium intervention. The degree that magnesium is better than placebo is small enough, many times, as to be seen as statistically insignificant.

Bottom Line: Magnesium may offer some benefit for leg cramping, but the evidence is still mixed.

Do They Lower Blood Pressure?

According to studies to date, magnesium supplements lower blood pressure, at best, to a small extent only.

A meta-analysis of 12 clinical trials found that magnesium supplementation for 8-26 weeks in 545 patients with high-blood pressure resulted in only a small reduction (2.2 mmHg) in diastolic blood pressure (the lower number)(18). The magnesium dose ranged from 243 to 973 mg/day.

In another meta-analysis of 22 studies with 1173 adults with either normal blood pressure, or high blood pressure, it was found that magnesium supplementation for 3-24 weeks decreased systolic blood pressure (the upper number) by 3-4 mm Hg, and diastolic blood pressure by 2-3 mm Hg (19).

When comparing these results to those from a study of the DASH (Dietary Approaches to Stop Hypertension) diet, we can put the benefits of magnesium supplementation on high blood pressure in to context!

The DASH diet has increased dietary magnesium intake from added fruits and vegetables, more low-fat or non-fat dairy products, and less fat overall. It was shown to lower both systolic and diastolic blood pressure by an average of 5.5 and 3 mmHg, respectively! However, this diet also increases intakes of other nutrients, such as potassium and calcium, which also can lower blood pressure. (20)

Bottom Line: Magnesium may lower blood pressure somewhat, but dietary magnesium from a healthy diet may be even more effective.

Do Magnesium Supplements Prevent Kidney Stones?

Calcium stones are the most common type of kidney stone, and magnesium and calcium tend to balance each other out. A study of 247 patients has found that magnesium citrate treatment, over three years, was effective at preventing the recurrence of (calcium oxalate and phosphate) kidney stones. (21)

The exact mechanism of its effect, however, is unknown. Laboratory studies have shown that the presence of magnesium destabilises calcium oxalate formation, and reduces the size of the stone formed. (22)

Bottom line: Magnesium supplements may play a role in preventing kidney stones; however, more human studies are needed to evaluate the effectiveness.

Are There Side Effects To Magnesium Supplements?


Can you have too much magnesium? Well, it depends.

In healthy individuals, having too much magnesium naturally present in food is not harmful and does not need to be limited. The kidneys can eliminate any extra amounts in the urine (23).

However, magnesium from supplements or medications should not be consumed above the upper limit, unless recommended by a health care provider. Otherwise, it could result in diarrhoea, nausea and abdominal cramping. (1,5) Extremely high intakes can lead to an irregular heartbeat and cardiac arrest.

Diarrhoea as a side-effect is most common with magnesium carbonate, chloride, gluconate and oxide (6).

Laxatives and antacids with very high doses of magnesium (ie. providing 5000 mg/day magnesium) have been linked with magnesium toxicity. At its worst, this could lead to muscle weakness, difficulty breathing, irregular heartbeat, and heart attack. (24)

Bottom Line: Over-dosing on magnesium through supplements is possible, but there are no side-effects from too much dietary magnesium.

Anyone Who Shouldn’t Take Them?

There are certain groups of people who need to be more careful with magnesium supplementation and should seek guidance from their healthcare professional. People with impaired kidney function or kidney failure have an increased risk of magnesium toxicity as their ability to remove excess magnesium is lowered or lost completely (1,23).

Magnesium supplements can interact or interfere with some medicines. People taking medications on a regular basis should discuss their magnesium intakes with their healthcare providers. Some examples include: antibiotics, diuretics, bisphosphonates (used to treat osteoporosis), and certain prescription drugs. (1)

What About Just Getting Magnesium From Food?


Good question.

For most of us, fulfilling our magnesium needs purely from our diet is actually our best bet – with little chance of getting it wrong. About 30% to 40% of dietary magnesium is typically absorbed by the body.

Magnesium is widely found in plant and animal foods, and also in beverages. Green leafy vegetables, such as silver beet, legumes, seeds, nuts, and wholegrains, are particularly good sources (1). As a guide, foods containing dietary fibre provide magnesium. It is also added to some breakfast cereals and other fortified foods.

Food processing of certain types, such as refining grains, lowers magnesium content quite a bit. Tap, mineral, and bottled waters can also be a source of magnesium, but the content varies. (1)

There are a number of websites and applications that can help give you an idea of how much magnesium you’re typically consuming. Otherwise, a dietician can offer advice.

Bottom Line: Fulfilling our magnesium requirements through dietary intake is usually adequate for most people, and the body is effective at maintaining the required magnesium balance through adjustment of absorption and excretion of the mineral.


For most of us healthy individuals with a well-balanced diet, there’s little chance that magnesium deficiency would be an issue – and taking a supplement may even take our levels over the edge.

Seems we’d be better off investing the money saved in some laxatives, for times when we really do need that extra magnesium!

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