Magnesium Deficiency: Signs, Best Food Sources and Supplements

Originally published 2016-08-03.

Magnesium deficiency means your body has less magnesium than it needs to run normally. In healthy people a true deficiency is uncommon, because the kidneys hold on to magnesium when intake is low. Low intake, on the other hand, is very common: a large share of adults eat less than the recommended amount. Early signs of real deficiency are vague, such as loss of appetite, nausea, tiredness and weakness, and more serious ones include muscle cramps, tingling and an irregular heartbeat. The most reliable fix for low intake is food: seeds, nuts, beans, leafy greens and whole grains. Supplements can help some people, but they have a safe upper limit and can interact with medicines, so a doctor should be involved if you suspect a problem.

This guide covers what magnesium does, who is most at risk, the signs worth noticing, the best food sources with real numbers, the main supplement types and a few popular claims that go further than the evidence.

What magnesium does in the body

An adult body holds about 25 grams of magnesium, and around half to 60 percent of it sits in the bones. Most of the rest is inside muscles and soft tissues; less than one percent is in the blood. Magnesium helps more than 300 enzyme systems work, including those that turn food into energy, build proteins and DNA, control blood sugar and regulate blood pressure. It is also involved in carrying calcium and potassium across cell membranes, which is why it matters for nerve signals, muscle contraction and a steady heart rhythm.

Because it touches so many processes, magnesium is often described online as a near-miracle mineral. It is genuinely essential, but being involved in many processes is not the same as curing many diseases, a distinction that matters when you read supplement marketing.

How much you need and who falls short

The US National Institutes of Health sets these recommended daily amounts for adults:

• Men: 400 mg a day at ages 19 to 30, and 420 mg from age 31.
• Women: 310 mg a day at ages 19 to 30, and 320 mg from age 31. Needs are somewhat higher in pregnancy.
• Teenagers: 410 mg for boys and 360 mg for girls aged 14 to 18.

US survey data suggest that about half of Americans get less magnesium from food and drink than they should, with teenagers and men over 70 among the lowest. Refined grains are part of the reason: milling wheat into white flour strips out much of the magnesium.

A few groups are more likely to develop an actual deficiency:

• People with digestive conditions such as Crohn's disease, coeliac disease or previous bowel surgery, which reduce absorption.
• People with type 2 diabetes, who can lose extra magnesium in urine.
• People with long-term heavy alcohol use.
• Older adults, who tend to absorb less and lose more.
• People taking certain medicines for a long time, notably proton pump inhibitors for acid reflux and some diuretics.

Signs of magnesium deficiency

Many popular lists online name stress, anxiety, poor sleep, migraines, low mood, weak bones and digestive upset as signs of low magnesium. These problems can be linked to magnesium in some people, but they have dozens of other causes, and none of them on its own means you are deficient. The symptoms that doctors associate with genuine deficiency develop in stages:

• Early: loss of appetite, nausea, vomiting, fatigue and weakness.
• As it worsens: numbness, tingling, muscle cramps and spasms, personality changes, abnormal heart rhythms and, in severe cases, seizures.
• Knock-on effects: severe deficiency can also lower calcium and potassium levels in the blood, which brings problems of its own.

Testing is not straightforward. A standard blood test measures serum magnesium, with a normal range of about 0.75 to 0.95 mmol/L, but because so little of the body's magnesium is in the blood, a normal result does not always reflect total stores. If you have ongoing cramps, palpitations or other worrying symptoms, talk to a doctor rather than guessing from a checklist; an irregular heartbeat in particular needs proper assessment.

Foods rich in magnesium

For most people, eating more whole foods is the simplest and safest way to raise intake, and there is no upper limit for magnesium from food in healthy people because the kidneys remove any excess. The body absorbs roughly 30 to 40 percent of the magnesium in a meal. Typical amounts per serving, from NIH data:

• Pumpkin seeds, 1 oz (28 g): 156 mg
• Chia seeds, 1 oz: 111 mg
• Almonds, 1 oz: 80 mg
• Spinach, boiled, half a cup: 78 mg
• Cashews, 1 oz: 74 mg
• Peanuts, quarter cup: 63 mg
• Soy milk, 1 cup: 61 mg
• Black beans, cooked, half a cup: 60 mg
• Edamame, half a cup: 50 mg
• Baked potato with skin, 3.5 oz: 43 mg
• Brown rice, cooked, half a cup: 42 mg
• Banana, medium: 32 mg

Other good choices include sesame and sunflower seeds, tofu, mung beans, flaxseed, oats, broccoli, peas and sweet corn. A practical day might include oats with seeds at breakfast, a bean or lentil dish at lunch, a handful of nuts as a snack and leafy greens with brown rice or a potato at dinner. That pattern alone can bring many adults close to their target.

You may read that modern soil is so depleted that food can no longer supply enough magnesium. Some studies have found lower mineral levels in certain crops than decades ago, but the size of the change is debated, and the foods above still provide meaningful amounts. Choosing whole grains over refined ones makes a far bigger difference.

Magnesium supplements: types and safety

If a doctor confirms that you need more magnesium, or you cannot meet your needs from food, supplements are widely available. The forms differ in how well they are absorbed and how likely they are to upset your stomach. Small studies suggest that aspartate, citrate, lactate and chloride forms are absorbed better than magnesium oxide and sulphate.

• Magnesium Chelate: magnesium bound to amino acids, a form generally well absorbed and often gentle on digestion.
• Magnesium Chloride Oil: a magnesium chloride solution sold for rubbing on the skin, often used for sore muscles. Evidence that meaningful amounts pass through the skin is weak, so it should not be relied on to correct a deficiency.
• Magnesium Citrate: magnesium bound to citric acid, well absorbed and also used as a laxative at higher doses.
• Magnesium Threonate: a newer, more expensive form studied for possible effects on the brain; human evidence so far is limited.
• Magnesium Glycinate: magnesium bound to glycine, popular with people who find other forms cause loose stools, and often marketed for sleep, though good-quality evidence for that is limited.

Safety points are important here. For adults, the upper limit for magnesium from supplements and medicines is 350 mg a day; this does not include food. Going above it commonly causes diarrhoea, nausea and stomach cramps. Very large doses, usually from laxatives or antacids, can cause dangerous drops in blood pressure and heart rhythm problems, and people with kidney disease are at particular risk because they cannot clear the excess.

Magnesium can also interact with medicines. It reduces absorption of some antibiotics (tetracyclines and quinolones) and of bisphosphonates used for osteoporosis, so doses need to be spaced apart, and certain diuretics raise or lower magnesium levels. If you take regular medication, ask a pharmacist or doctor before starting a supplement.

Claims versus evidence

Magnesium attracts bold claims on wellness sites and social media. Here is what reliable reviews actually say:

• "Every illness is linked to magnesium deficiency." This idea is often attributed to the American physician Norman Shealy, but there is no scientific evidence that magnesium deficiency underlies all disease.
• "Magnesium has been proven to treat diabetes, asthma and depression." Not proven. Low magnesium intake is associated with a higher risk of type 2 diabetes, but trials of supplements conflict, and the American Diabetes Association says the evidence is insufficient to recommend them for blood sugar control.
• Blood pressure. Supplements may lower blood pressure slightly, by around 2 to 4 mmHg in some analyses; the US Food and Drug Administration describes the evidence as inconsistent.
• Migraine. Major headache societies consider magnesium probably effective for preventing migraine, but the doses used are above the supplement upper limit, so this should be done with a doctor's guidance.
• Heart and stroke. Higher dietary intake is linked with lower risk of stroke and heart disease in observational studies, which is encouraging, but large trials have not yet shown that supplements prevent them.
• "Almost everyone is deficient." Many people eat less than recommended, but clinical deficiency in healthy people is uncommon.

The balanced takeaway: magnesium is essential, many diets are short of it, and improving your intake through whole foods is sensible for almost everyone. Supplements are useful in the right situation, but they are not a cure-all, and anyone with symptoms, kidney problems or regular medication should talk to a doctor first.

Sources: NIH Office of Dietary Supplements: Magnesium fact sheet for health professionals; original article idea from Unisoul Theory. This page is for general information and is not medical advice.