Tired in the afternoon, a few more hairs in the brush, the odd cramp at night. Put those into any online checklist and you'll come out missing iron, magnesium, B12, vitamin D and half the alphabet, usually with a supplement bundle waiting at the bottom of the page. Going by those lists, the whole human race is running on empty.
Real shortfalls do happen, and they matter when they do. What gives one away is rarely a symptom. It's usually something about your life: what's on your plate, what your body is going through, or a tablet you've taken every morning for years.
Why symptom lists mislead
Tiredness has dozens of causes, from short sleep to a slow thyroid to plain stress, and a deficiency is only one of them. Hair loss, cramps, low mood and brittle nails are the same: each one points in several directions at once. By the time a deficiency produces clear signs of its own, it has usually been building for months. Why Am I Always Tired, linked below, sorts ordinary tiredness from fatigue with a cause.
The trick is older than the internet. In 1948 the psychologist Bertram Forer gave his students what they took to be personal readings, and they rated them 4.3 out of 5 for accuracy. Every student had the same text, assembled from a newsstand astrology book. A symptom list works the same way, with a checkout at the end.
Not every sign is a dead end, though. Wanting to chew ice is a recognised clue to low iron, and pins and needles alongside a sore, red tongue point towards B12 or folate. The Quiet Signals of Mineral Deficiency, linked below, goes through the mineral ones.
A better starting point is your life. Deficiencies follow what you eat, what your body is going through, how well your gut absorbs, and what medicines you take. Look at those four and you can usually tell which one or two nutrients are worth checking, and which test will answer the question.
What's on your plate
Plant diets have the clearest risks. Vitamin B12 is found almost only in animal foods. Without them it has to come from fortified foods or a pill, and a vegan mother who breastfeeds hands the shortage on to her baby. B12 is only where the list starts. Why Eating Well Isn't Enough Anymore has the rest of the pills a plant diet ends up needing, and how little an animal eaten nose to tail leaves out.
Iron from plants is absorbed less well than iron from meat, and Popeye is no help here. Spinach got its name for iron through a measurement mistake, and Why Spinach Needs Butter, and Other Food Pairings has what he should have been eating it with.
Iodine is the easiest one to forget. Fish, shellfish, eggs and dairy are the best sources, and seaweed carries the most of all, sometimes more than is good for you in a single serving. Sea salt and pink salt hold very little iodine, so a good unrefined salt, which I'd still choose, leaves your iodine to your food. Iodised salt fills that gap only if it's the salt you use, since processed food is usually made with the plain kind. Zinc can run low on a plant diet as well, because compounds in whole grains, beans and seeds hold on to it in the gut.
Carnivore and keto eaters have a different list. In the first weeks of cutting carbohydrates, the body lets go of water, and it loses sodium, potassium and magnesium in the process. That's a common explanation for the headache, weakness and cramping known as keto flu, which tends to settle once those minerals are topped up. For the salt, a good unrefined salt on your food does it, with care if your blood pressure runs high or your heart or kidneys need watching. On a meat-only diet, iodine is easy to get from eggs, fish and dairy, and easy to miss on beef alone.
Vitamin C is the question every meat eater gets asked, usually with the word scurvy attached. British sailors were nicknamed "limeys" after the lime juice meant to keep it away, but the juice was weaker than its reputation. The navy had swapped Mediterranean lemons for West Indian limes, which carry far less vitamin C, then served the juice after light, air and copper piping had worked on it. A 1918 animal test of navy lime juice found almost no power against scurvy at all.
Fresh meat did better. On Scott's 1902 Antarctic expedition, fresh seal meat, with a bigger ration of bottled fruit, brought the men back from the first signs of scurvy in under two weeks. Fresh meat and organ meats above all carry vitamin C of their own. Bleeding gums would be an early sign to watch for.
Long stretches of low-calorie dieting shrink everything at once. Eat less food for months and you eat fewer vitamins and minerals along with the calories, which makes a strict diet with a narrow menu a well-worn road to a shortfall.
What your body is going through
Heavy periods are a leading cause of low iron in women, and they're easy to overlook because they feel normal to the person having them. Pregnancy and breastfeeding push up iron, folate and iodine needs all at once. Folate counts even before conception, since the neural tube, which becomes the brain and spinal cord, closes within the first month, often before a woman knows she's pregnant.
Folate's story starts among poor pregnant women in Bombay's textile industry, where around 1930 Lucy Wills was chasing a severe anaemia. Yeast extract could prevent and cure it, and the cheapest source was Marmite. Folate turned out to be what the yeast was supplying.
Choline is the pregnancy nutrient that rarely gets a mention. In a US survey, 90 to 95 percent of pregnant women ate less than the recommended amount, prenatal supplements usually carry little or none, and no routine test tracks it, because blood levels hold at half of normal or more even after fasting. Liver and eggs are the richest sources by far.
Endurance athletes lose iron through sweat and through the pounding their feet take, and regular blood donors give some away with every donation. Teenagers grow fast and eat unpredictably, which makes iron a common gap once periods start, and vegan teenagers need B12 as much as vegan adults do.
Age changes absorption. Low stomach acid grows more common after about fifty, and B12 in food needs that acid to be released, so you can eat plenty of B12 at seventy and still run low. Vitamin D depends on sunlight on bare skin. Long days indoors, skin kept covered, and darker skin far from the equator all put you at the front of the queue, and older skin makes less of it too. Season matters as well: far from the equator the sun sits too low for part of the year, and from roughly October to March skin makes little or none, however long you spend outside. If the rest of that list fits you, those are the months when a vitamin D3 supplement earns its place.
How well your gut absorbs
A healthy diet only counts once it's absorbed. Coeliac disease damages the part of the small intestine that takes up iron, folate and calcium, so unexplained low iron is one of its classic first signs. Across 18 sets of patients with iron-deficiency anaemia, about 1 in 31 turned out to have it. Crohn's disease, long-running gut inflammation and weight-loss surgery all cut absorption too, and having part of the stomach or bowel removed usually means having your levels checked for life. Heavy drinking adds its own losses, most of all thiamine, folate, magnesium and zinc.
Pernicious anaemia belongs on this list, and the NHS calls it the most common cause of low B12 in the UK. The immune system attacks healthy cells in the stomach, and B12 from food can no longer be absorbed the normal way, so a plate full of it can still leave you short.
What's in your medicine cabinet
Some everyday medicines lower nutrient levels too slowly for the two to look connected. Metformin, the common tablet for type 2 diabetes, reduces B12 absorption over years. Acid-reducing tablets, taken long term, lower both B12 and magnesium. Water tablets for blood pressure and fluid can drain potassium and magnesium. Stay on the medicine, and have the nutrient it affects checked every so often.
One thing that never came from a pharmacy belongs here too. Nitrous oxide, laughing gas, comes in small canisters meant for whipped cream, and when it's breathed for the high it knocks out B12 in the body. In 100 published cases, more than half from recreational use, the usual picture was tingling and an unsteady walk, and most had low B12. Teenagers of 14 to 18 have been admitted to hospital with the same spinal cord damage. With those symptoms in a young person, ask about it directly.
Which test fits
For iron, the useful test is ferritin, which shows how much iron you have in storage, usually with a full blood count. Inflammation pushes ferritin up, so a normal result during an infection or a flare of something inflammatory can hide low stores. A finger-prick kit such as an or an can be a reasonable start, as long as it reports a number.
For B12, a standard blood level is the start. When the result sits in the grey zone near the bottom of the normal range, a second test, methylmalonic acid, shows whether your cells are short of it.
Folate is trickier. A standard blood level mostly reflects what you've eaten recently, so a few good days can flatter it. A red cell folate test shows the longer picture. Homocysteine, sometimes offered as a check, rises with low folate but also with low B12 and with kidney problems, so on its own it can't say which one is short.
For vitamin D, the test to ask for is 25-hydroxy vitamin D, and it's the one to think twice about. The Endocrine Society's 2024 guideline found no evidence from controlled tests in favour of routine testing in the general population, nor in those with obesity or dark skin, and no clear target level for preventing disease. Let your life make the case for it first.
Magnesium is harder. Almost all of it sits inside cells and bone, so blood can look fine while stores are low, and your diet, medicines and symptoms tell you as much as the number. Calcium is the same story, told louder. Nearly all of it is locked in the skeleton, so a blood level says little about how much you have, and a bone density scan shows the lifetime account instead. Iodine and zinc have no reliable single blood test for an individual, which makes looking at your diet the practical check for both. Hair mineral analysis, sold online to answer all of these at once, is another matter. The Quiet Signals of Mineral Deficiency tells the story of one person's hair sent to six laboratories.
Whatever the test, ask for the number as well as the verdict. "Normal" depends on where the line is drawn. Across a US national sample of 3,490 females aged 12 to 21, the share counted as short of iron was 17 percent with the ferritin line at 15, 38.6 percent with it at 25, and 77.5 percent with it at 50. The blood samples were the same in all three. A result at the bottom of the range, or one that keeps falling from one test to the next, tells you more than the label does.
Before any blood test, if you take biotin, stop it a few days beforehand. It's in plenty of hair, skin and nail supplements and in multivitamins, and it can throw off a range of lab results, including thyroid tests, making them look better or worse than they are. The result that worries the FDA most is troponin, the blood test for a heart attack. Biotin can push it falsely low, and in 2017 the agency reported one patient on high levels of biotin who died after such a result. Some of those tests have since been fixed, and when one such test was checked, the odds of a missed heart attack came out at about 0.03 percent. In an emergency, say you take it.
Fix what's low, and stop there
Once you know what's low, food is the first fix. Red meat, liver and shellfish are the richest sources of iron, B12 and zinc together, and the iron in them is the form the body takes up most easily, though liver is best left out during pregnancy because of its high vitamin A content. Folate takes its name from folium, the Latin for leaf, yet a serving of beef liver carries more of it than a serving of boiled spinach. Oily fish and eggs bring vitamin D, and fish, eggs and dairy bring iodine. Magnesium is the honest gap on a meat-heavy plate: fish and meat carry a modest amount, and nuts and seeds carry more. Food closes a gap with a whole package of other nutrients attached. When the gap is large, or your diet rules a food out, a supplement does the job faster.
When you do take one, how you take it counts as much as what's in it. Iron goes in best away from tea, coffee and calcium, dairy included. The vitamin C so often taken with it turns out to be optional, because a test of 440 anaemic adults found the tablets worked just as well without it. Vitamin D goes in better with the biggest meal of the day. And the B12 in supplements such as and in fortified foods is already in a form that needs no stomach acid, which is why it works after fifty, when food B12 may no longer get through.
More of a good thing is a poor rule, though. Iron can build up in the body when you take it without needing it, and an inherited overload condition, haemochromatosis, makes that far worse. Across 99,711 adults screened in North America, about 1 in 227 non-Hispanic white participants carried two copies of the gene change behind most cases. If it runs in your family, the blood tests that catch it are transferrin saturation, which shows how much iron is carried in the blood, and ferritin, and a gene test settles it. Vitamin D can climb too high with long-term large amounts, and a daily multivitamin taken on the off chance rarely fixes a real shortfall while adding plenty you never needed.
Folic acid has a catch of its own. Large amounts can correct the anaemia that low B12 causes, but not the nerve damage, and the concern is that the shortage stays hidden until that damage can't be undone. That question isn't settled, but it makes a strong case for knowing your B12 before taking much folic acid.
Recheck after a few months, so you know the fix worked and when to ease off.
Start with your own list
The checklists work backwards, from symptoms we all get to nutrients we all seem to lack, and they end at a shopping basket. Start from your own life instead: your plate, your body, your gut and your medicine cabinet. That usually points to one or two nutrients at most, and one or two tests that settle the question. The afternoon tiredness might still turn out to be short sleep. At least you'll know, and the supplement bundle can stay in the basket.
Go through those four today, write down the nutrients that match your life, and get the test for the one that comes up most.
Want to know which mineral signs are real? The Quiet Signals of Mineral Deficiency — seven minerals, the signs that hold up, the ones that are folklore, and which tests can be trusted.
Tired all the time, however much you sleep? Why Am I Always Tired: When Chronic Exhaustion Has a Cause That Sleep Can't Fix — how to tell ordinary tiredness from fatigue with a cause, from minerals to thyroid to stomach acid.
Know someone who's bought a supplement bundle after an online checklist? Send them this. It might point them to the one test that settles it.
Tried something here, or got a question it didn't answer? Write to us at contact@allforlife.club. Your questions shape the next articles.
Disclaimer: This article is general information. For advice about your own diet, medication or health, talk to a qualified health professional. If you're pregnant or planning a pregnancy, take regular medication, or have a gut condition, get professional advice before starting or changing supplements, and have your levels checked rather than guessing.
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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