A cramp in the calf that wakes us at night is the best-known mineral signal there is, and magnesium is the best-known answer. Put to the test, the answer failed. Pooled across five tests and 307 people, most of them older adults with cramps at night, magnesium changed the count by under a fifth of a cramp a week. Just as many people improved on the dummy pill.
So the most famous quiet signal points somewhere else. Others hold up well. A craving for ice, a nail that dips like a spoon and legs that will not keep still in bed all lead back to one mineral, and a blood test confirms it.
Minerals have neither the marketing budget of protein powders nor the cultural moment of vitamin D. What they have is folklore. White spots on the nails mean zinc. A twitching eyelid means magnesium. A lock of hair can read the lot. Some of the folklore is right, and it pays to know which part.
This article sorts the signs of mineral deficiency one mineral at a time. For each of seven we ask the same things: which signals are real, which ones it only gets blamed for, who runs low, and whether the test can be trusted.
First, the cramp
If magnesium is not the answer to a night cramp, something else has to be.
What does help. Stretching and massaging the muscle while it lasts, and regular calf stretches to make cramps rarer. The usual causes are plain ones: getting older, a hard day on the legs, pregnancy, too little to drink, and some medicines.
Salt and sweat. Cramps after heavy sweating are a separate case, and here minerals may well matter. Ten men ran downhill in the heat until they had sweated out 2% of their body weight. When they then drank plain water, their muscles cramped more easily than before, and the sodium in their blood had fallen. When they drank water with electrolytes in it, their muscles became harder to cramp.
Against that, among 210 Ironman triathletes, the 43 who cramped had the same blood electrolytes and the same fluid loss as the rest. What marked them out was racing faster. So the picture is mixed, and the cheap precaution after a long sweat is a drink with electrolytes in it, such as .
Iron: the one that talks
Iron is the mineral that sends real signals, and plenty of them. Lack of it is the commonest nutritional cause of anaemia in the world.
The real signals. The loud ones are tiredness, breathlessness, pale skin and a heartbeat we can feel. The quiet ones are more telling: cold hands and feet, a craving for ice, nails that flatten into a spoon, a sore tongue, hair coming out in the brush, legs that will not settle at night, and a ringing in the ears.
Cracks at the corners of the mouth belong here too, with a caution. The usual cause is saliva sitting in the creases. When the cracks keep coming back, low iron is on the list, along with low zinc and some of the B vitamins.
Who runs low. Women with heavy periods, pregnant women, regular blood donors, and anyone eating little or no meat.
The test. Ferritin, alongside a blood count. Ferritin measures the iron we hold in store, and it falls before the blood count does. Here the blood test catches the problem early.
The food. Meat, fish and poultry carry haem iron, which the body absorbs better than the iron in plants. What we drink with the meal matters as much. A cup of tea with a hamburger meal cut the iron absorbed from it by 64%, and a cup of coffee by 39%. Coffee an hour before the meal made no difference. Coffee an hour after did the same damage as coffee with it. Even the pan counts: in three tests, food cooked in iron pots raised the blood counts of people who were anaemic or low in iron.
The patience. Red blood cells live for about four months. The pale, under-filled cells made during the shortage keep circulating until their time is up, so the tiredness lifts slowly, even when the iron is going back in. People try for two or three weeks, feel no different, and conclude it was never the problem.
Iron is one to test for, never to guess at. Too much does harm.
Magnesium: the one that gets the blame
Magnesium has a hand in so much of the body's chemistry that almost any symptom can be pinned on it, and most have been.
There is a reason it attracts suspicion. Eating less magnesium than the recommended amount is common. A shortage that causes symptoms is uncommon in healthy people. The supplement shelf lives in the gap between the two.
Blamed on it. Night cramps, as the opening showed. And the twitching eyelid: twitches are linked to tiredness, stress, caffeine and alcohol, and to some medicines. They are rarely a sign of anything missing.
The real signals. A true shortage starts with loss of appetite, nausea, tiredness and weakness. Further on come numbness, muscle cramps and an irregular heartbeat.
Who runs low. People with long-standing gut disease, type 2 diabetes or alcohol dependence, and older adults. Two kinds of medicine drain it as well: water tablets, and the tablets that reduce stomach acid. The UK medicines regulator has warned that the acid tablets can pull magnesium down, in some cases after three months and in most after a year, and that the signs "may begin insidiously and be overlooked". That is a quiet signal worth the name.
The test. This is where the old complaint about blood tests is fair. Most of the body's magnesium sits inside cells and in bone, and the blood level, in the words of the US National Institutes of Health (the NIH), does "not accurately reflect" the total. A normal result leaves the question open. The better clues are the ones in the paragraph above: what we take, what we drink, and what else is going on.
The food. Green leafy vegetables, nuts, seeds, beans and whole grains. The body absorbs about a third of what is in them.
The bath. Magnesium's best-known product is older than the supplement aisle. In 1618 a farmer at Epsom in Surrey found that his cows would not touch the water from one well, it was so bitter. The salt left behind when that water was boiled away became Epsom salts, and it is magnesium sulphate. In a bath, is a pleasure. As a way of getting magnesium into the body, reviewers found the claims "scientifically unsupported".
Should we take it? For cramps and twitches, the case is thin, as we have seen. One use has backing: the neurology societies rate magnesium "probably effective" for preventing migraine. Forms differ. The kinds that dissolve well in water, such as citrate, are absorbed better than oxide. Too much of any of them loosens the bowels.
Potassium: the one we lose
Potassium is pot ash. Its salts were first made by soaking the ash of burnt wood in a pot, and the name stuck.
The real signals. Constipation, tiredness and weak muscles. A serious shortage disturbs the heartbeat.
Who runs low. Diet is seldom the cause. Potassium is lost: through water tablets, laxatives, a long bout of diarrhoea or vomiting, or heavy sweating. Eating clay does it too, which gives the oldest odd craving a second mineral to answer for.
The test. A routine blood test measures it.
The food. Potatoes, fruit, beans, milk, meat and fish.
Zinc: the one with the nail myth
The real signals. A dulled sense of taste and smell, at any age. Wounds that are slow to heal, mostly in older adults. In children, hair loss and one infection after another.
Blamed on it. White spots on the nails. They have been put down to calcium for generations and to zinc more recently, and both are wrong. The commonest cause is a knock to the base of the nail, where the nail is made. The spot grows out with it.
Ringing in the ears is another. When zinc was tested against a dummy pill for tinnitus, it made no difference to the loudness.
Who runs low. People with gut disorders or weight-loss surgery behind them, people on vegetarian and vegan diets, pregnant and breastfeeding women, and heavy drinkers. In richer countries a real shortage is unusual.
The test. A blood test exists, with what the NIH calls "important limitations". The level shifts with age, sex and the time of day, and does not always follow what we eat. Diet and history say more.
The food. Oysters are far ahead of everything else, and a tin of keeps in the cupboard. Meat, fish, eggs and dairy follow. Beans, nuts and whole grains contain zinc too, but the body takes up less of it from them.
Too much. Taken in excess for a long time, zinc lowers copper. The strangest route is denture cream. Some creams contain zinc, and people using far more than the label says have ended up short of copper, with numbness and weakness in the arms, legs and feet.
Iodine: the forgotten one
Iodine means violet. In 1811 Bernard Courtois was burning seaweed for the chemicals France needed to make gunpowder, added too much acid to the ash, and watched a cloud of violet vapour rise.
In the body iodine has one job: the thyroid builds its hormones from it. The classic signal of a shortage is a goitre, a swelling at the front of the neck. It was once common enough in the English Midlands to be called Derbyshire neck. Switzerland, where goitre was everywhere, began adding iodine to salt in 1922, in the world's first programme to fortify a food. A mild shortage sends no signal at all, which is what makes the next two findings uncomfortable.
When 737 urine samples from schoolgirls across the UK were measured, 51% showed mild iodine deficiency and 16% moderate. And among 1,040 mothers and children followed from pregnancy, the children of women who were low in iodine in the first three months were more likely to land in the bottom quarter for verbal IQ and for reading at eight and nine.
Who runs low. Anyone who eats little fish, eggs or milk. The need rises in pregnancy.
The test. There is no good one for a single person. Iodine is measured in urine, and one sample says more about a country than about any of us, which is how the schoolgirls were counted. The guide is the plate.
The food. Milk, eggs, sea fish and shellfish. Plant-based drinks carry iodine only when it has been added, so the label is worth a look.
Salt is a poorer source than its history suggests. Sea salt, Himalayan salt and kosher salt are not usually iodised, and plain sea salt provides, in the NIH's words, "virtually no iodine". The salt in processed food is almost always the plain kind too.
Selenium: decided by the soil
Selenium is named for the moon. The chemist Berzelius found it in 1817 beside tellurium, which is named for the Earth, and called it after the Greek selene. On the plate it behaves more like the ground. Selenium gets into food from the soil, so where our food is grown matters more than what we choose.
Finland found its soil so poor in selenium that in 1984 it began adding the mineral to fertiliser across the country. At the last report it was still the only country to have done so. Selenium in grain rose 15-fold, and the level in people's blood climbed into the optimal range. Rates of heart disease and cancer stayed where they were.
In parts of China where the soil is poorer still, a shortage was tied to Keshan disease, a failure of the heart muscle that killed thousands at its peak in the 1960s. Outside such places, in the words of the NIH, a shortage on its own "rarely causes illness".
The signals belong to the other end. Too much selenium brings hair loss, brittle nails and breath that smells of garlic. The mineral sold for hair and nails damages both in excess.
The food. Fish, meat, poultry and eggs. Brazil nuts hold so much, about a day's need in a single nut, that eating too many goes over the safe upper limit.
Selenium is sold for the thyroid as well. The NIH's summary is that the supplements "do not provide much benefit for the thyroid".
The test. A blood level. It is seldom needed outside the regions with poor soil.
Calcium: the silent one
Calcium sends no quiet signals. Nearly all of it is in the skeleton, and the body keeps the level in the blood steady by drawing on the bones. That is why, in the NIH's words, blood levels "are not a good reflection" of how much calcium a person has. The measure that counts is a scan of bone density.
So the first signal is often the worst one. Thinning bones are, as the NHS puts it, "often only diagnosed when a fall or sudden impact causes a bone to break".
The supplement question. Across five tests and 8,151 people, 143 of those taking calcium tablets had a heart attack, against 111 of those on a dummy pill. That is about 30% more, and a good reason to put food first.
The food. Milk and yoghurt, tinned sardines and salmon eaten with their bones, kale and broccoli. The body absorbs about 30% of the calcium in dairy and less from some plants. It needs vitamin D to absorb it well.
The test that fails
Hair analysis promises to read every mineral from a snip of hair, and it is sold directly to anyone who wants it.
It has been put to the test. Hair from one healthy volunteer was split and sent to six laboratories, which between them handled 90% of such tests in the United States. For 12 minerals, the highest and lowest results differed more than tenfold. The laboratories disagreed on what counted as normal, so the same hair was high, normal and low in nearly every mineral, depending on where it went. They also sent back conflicting advice on which supplements to buy.
Hair is no use as a general gauge, then. It has one narrow job: clippings are used to follow long-term selenium intake. A single mineral measured for a purpose is a long way from a panel of thirty.
What drains minerals
Medicines. Acid-reducing tablets and water tablets, as above. Keep taking them, and ask to have the mineral checked now and then.
Alcohol. Heavy drinking lowers magnesium and zinc.
The gut. Coeliac disease and long-running inflammation of the bowel cut what is absorbed, iron above all.
The cup with the meal. Tea and coffee, for iron.
The first weeks of low-carb. Cutting carbohydrates sheds water, and salt, potassium and magnesium leave with it. That is much of the headache and tiredness known as keto flu. In people's own accounts it peaks in the first week and fades within four.
The soil? The claim is that crops hold far less than they used to. One comparison of official figures for 43 garden crops found six nutrients lower in 1999 than in 1950, calcium, phosphorus and iron among them, by between 6% and 38%. Its authors put this down mainly to newer varieties bred for size and yield. About a quarter of the changes they could measure were increases.
There is a term for running short of minerals and vitamins while eating plenty: hidden hunger. It was coined for the more than two billion people whose food supplies enough energy and too little else.
How to read a quiet signal
One sign has many explanations. A twitch is a late night. A cramp is a long walk. A white spot is a door frame.
Several signs from the same mineral, in someone with a reason to be low, are different. The reason matters as much as the signs: a medicine taken for years, a food group left out, heavy periods, a gut that has never been right.
So write them down: the signs that keep coming back, and beside them what we take and what we avoid eating. Then test the one mineral the list points to.
A daily multivitamin "just in case" is the other temptation. Among 390,124 healthy adults followed for up to 27 years, those who took one every day lived no longer than those who took none.
A handful of single minerals is no safer, because they compete. Too much zinc lowers copper and, in very large amounts, the magnesium we absorb. Iron tablets taken with zinc cut the zinc that gets through. Iron itself is absorbed best when it is taken apart from calcium. Fix what is low, and stop there.
One caution before any supplement. The kidneys clear the magnesium and potassium the body has no use for, so anyone whose kidneys are not working well should ask before taking either. The NHS adds that older people should not take potassium supplements unless they have been advised to.
Go back to the three signs most lists open with. The cracked corner of the mouth is sometimes iron. The twitching eyelid is a short night and a strong coffee. The cramp in the calf is neither, whatever the label on the magnesium says, and a daily calf stretch is the better bet.
Start with the list tonight.
Not sure whether you have a reason to be low? Nutrient Deficiencies: Who's at Risk and Which Test to Get — who runs short of what, and the test that shows it.
Want the wider picture of what a symptom can mean? 12 Signs Your Body Is Trying to Tell You Something Important — twelve common signals, what each usually is, and the test that settles it.
Know someone who takes magnesium for their night cramps? Send them this, and show them the calf stretch.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional. If a symptom is new, lasting or getting worse, get checked.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
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