30/09/2026
The Body Doesn't Send Emails
Your body has no inbox.
It has no memo function and no polite reminder that you're running low on magnesium on Thursday.
What it has is symptoms.
Tired. Twitchy. Foggy. Flaky.
Hair in the plughole in quantities that would embarrass a Labrador.
We tend to file these under personality ("I'm just a tired person") or cover them with concealer, coffee and a bit of denial. Sometimes that's fine, because sometimes tired is just tired. But sometimes the body is sending the only message it knows how to send, and the message is: *something I need is running low.*
Here are the common ones, and how much weight each deserves.
Iron
* What it looks like:
exhaustion that sleep doesn't fix, weakness, trouble concentrating, pale skin, breathlessness, cold hands and feet.
The stranger clues are on the NHS list too: a craving to chew ice or paper (pica), spoon-shaped nails, restless legs, and sore cracks at the corners of the mouth. Hair shedding gets blamed on iron a lot; it has many other causes, so treat it as a hint only.
* Who's at risk:
heavy periods, pregnancy, frequent blood donors, coeliac disease and inflammatory bowel disease.
Vegetarians need roughly 1.8 times more iron than meat-eaters, because plant iron is harder to absorb. Long-term acid-reducing medication (proton pump inhibitors) can also cut absorption.
* Good to know:
stores run down before the blood count drops, so you can feel rotten while a basic haemoglobin test looks fine. Ferritin is the test that shows the stores (below 30 mcg/L suggests deficiency), though inflammation can push ferritin up and hide a problem.
* The catch:
iron is one of the few nutrients you can genuinely overdo, and people with haemochromatosis absorb too much of it.
Test first.
Supplement second.
Keep the tablets away from children, because iron overdose is a leading cause of fatal poisoning in under-sixes.
Vitamin B12
* What it looks like:
fatigue, a sore inflamed tongue, pins and needles in the hands and feet, palpitations, pale skin, memory and thinking trouble.
Low mood turns up in the research too, though the link is an association, not proof.
* Who's at risk:
vegans (B12 lives in animal foods, so it has to come from fortified food or a supplement), older adults (stomach changes with age cut absorption), people with pernicious anaemia, gut conditions or gut surgery, and people on metformin or long-term acid-reducing drugs.
* Why it matters:
the body stores years' worth, so symptoms creep in slowly. The nerve symptoms can appear *without* anaemia, and the damage can become irreversible. Tingling is a reason to book a blood test.
* The flip side:
if your B12 is normal, extra doesn't buy you energy. Studies show no performance boost in people who aren't deficient.
Vitamin D
* What it looks like:
in proper deficiency, bone pain and weakness (osteomalacia in adults, rickets in children), plus muscle weakness and aching.
* The honest bit:
you'll see vitamin D blamed for low mood and constant colds. Low levels are linked to depression in observational studies, but trials of supplements haven't shown they treat or prevent it. The "catches every bug going around" claim didn't hold up in the sources I checked, so it's out. What *is* solid is the bone and muscle picture.
* Sun facts:
UVB doesn't pass through window glass. Season, latitude, cloud, age and skin melanin all change how much you make. Sunscreen use plays a smaller role than people assume, because most of us apply too little to block it fully.
* Testing:
the marker is 25-hydroxyvitamin D. Under 30 nmol/L (12 ng/mL) is the deficiency-risk zone; 50 nmol/L (20 ng/mL) or above is adequate for most. Labs use different assays, and no major body recommends routine testing for healthy adults, so test if you have symptoms or a real risk factor (little sun, dark skin, older age, fat malabsorption, obesity or gastric bypass).
Magnesium
* What it looks like:
early on, loss of appetite, nausea, fatigue and weakness. Later, numbness, tingling, muscle cramps and contractions, personality changes and abnormal heart rhythms.
* The honest bit:
in healthy people, true deficiency from diet alone is uncommon, because the kidneys hold on to magnesium when intake drops. It usually has a cause behind it: heavy alcohol use, gut disease, type 2 diabetes, diuretics, or acid-reducing drugs taken for more than a year. Less than 1% of your magnesium sits in the blood, so a "normal" blood result doesn't guarantee healthy stores either.
* The catch:
supplement magnesium above 350 mg a day tends to arrive as diarrhoea.
Zinc
* What it looks like:
cuts that heal slowly, more infections, hair loss (best documented in children), skin changes, and a dulled sense of taste or smell.
* Who's at risk:
inflammatory bowel disease, coeliac disease, heavy drinking, pregnancy, and vegetarian and vegan diets (the phytates in grains and beans bind zinc).
* The catch:
50 mg or more for weeks can block copper absorption, and low copper brings its own nerve and blood problems. The adult upper limit is 40 mg a day. Iron supplements of 25 mg or more taken with zinc also cut zinc absorption.
Vitamin C
* What it looks like:
fatigue, swollen bleeding gums, small red or purple spots on the skin, aching joints, wounds that won't close, coiled corkscrew hairs, loose teeth, low mood. That's scurvy, and it is rare now. It takes weeks of almost no vitamin C (under about 10 mg a day) to develop. Smokers need 35 mg a day more than non-smokers, and very restricted diets or serious malabsorption raise the risk.
Folate (B9)
* What it looks like:
weakness, tiredness, trouble concentrating, irritability, headaches, palpitations, breathlessness, sores in the mouth and on the tongue, and colour changes in skin, hair or nails.
* Why it matters:
low folate before and in early pregnancy raises the risk of neural tube defects, which is why anyone who could become pregnant is advised to take 400 mcg of folic acid daily.
* The catch:
high-dose folic acid can clear the anaemia of B12 deficiency while the nerve damage carries on. Another reason to test rather than guess.
Iodine
* What it looks like:
a swelling at the base of the neck (goitre) is often the first visible sign. Iodine builds thyroid hormone, so a shortage can bring tiredness, feeling cold and weight gain, but those have plenty of other causes.
* Who's at risk:
people who don't use iodised salt, people who eat little seafood, dairy or eggs, and pregnant women (who need about 50% more). Sea salt and Himalayan salt are usually *not* iodised, and processed foods almost never use iodised salt.
* The catch:
too much iodine can also cause goitre.
Vitamin A
* What it looks like:
trouble seeing in dim light is the early sign. Left untreated it can lead to blindness, and long-term deficiency raises the risk of infections and anaemia. It's rare in wealthy countries; people with cystic fibrosis, Crohn's, ulcerative colitis or coeliac disease are the ones most at risk.
* The catch:
preformed vitamin A (retinol) is fat-soluble, so it builds up. Too much causes headaches, blurred vision and nausea, and it can cause birth defects in pregnancy. The adult upper limit is 3,000 mcg a day. Beta-carotene from food is harmless, but high-dose beta-carotene supplements raise lung cancer risk in smokers and ex-smokers.
Biotin
* What it looks like:
thinning hair, brittle nails, and a scaly red rash around the eyes, nose and mouth.
* The honest bit:
biotin deficiency is rare. It has never been reported in healthy people eating a normal mixed diet. The evidence that supplements improve hair or nails in healthy people is thin (a few small studies, none with a placebo group). Raw egg white blocks absorption, and so does heavy drinking.
The Body Doesn't Send Emails (the fine print)
Every symptom above has at least three other possible causes. Fatigue alone can come from thyroid trouble, poor sleep, depression, anaemia, infection, blood sugar swings, or a life that needs a holiday.
That's why guessing is a poor plan:
- You can take the wrong thing for months while the real cause carries on.
- Some minerals compete with each other (zinc and copper; iron and zinc; calcium may also reduce iron absorption).
- Biotin, the darling of the hair-and-nails aisle, can throw off blood tests, including thyroid and heart markers. Even a single 10 mg dose has interfered with thyroid tests, and the FDA has reported a death after a falsely low heart-attack (troponin) result in someone taking high-dose biotin. If you take it, tell whoever reads your results.
- High-dose vitamin B6 taken for a year or more can cause serious nerve damage (it usually eases once you stop). The US upper limit is 100 mg; the European limit is 12 mg.
The plain approach:
notice the pattern,
write down how long it has lasted,
get bloods done for the likely suspects, and fix what the results show.
Eat the boring, varied, colourful diet first, because food delivers nutrients in the company they evolved with.
Your body is doing its best to talk to you. It just hasn't got the vocabulary for anything but symptoms.
So LISTEN. THEN CHECK THE BLOODS.
*This post is general information and not medical advice. If something on this list sounds like you, see a GP or doctor before supplementing.*
**Sources**
- NIH Office of Dietary Supplements fact sheets: [Iron](https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/), [Vitamin B12](https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/), [Vitamin D](https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/), [Magnesium](https://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/), [Zinc](https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/), [Vitamin C](https://ods.od.nih.gov/factsheets/VitaminC-Consumer/), [Folate](https://ods.od.nih.gov/factsheets/Folate-Consumer/), [Iodine](https://ods.od.nih.gov/factsheets/Iodine-Consumer/), [Vitamin A](https://ods.od.nih.gov/factsheets/VitaminA-Consumer/), [Biotin](https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/), [Vitamin B6](https://ods.od.nih.gov/factsheets/VitaminB6-Consumer/)
- NHS: [Iron deficiency anaemia](https://www.nhs.uk/conditions/iron-deficiency-anaemia/)
Iron overview for health professionals. Research health effects, dosing, sources, deficiency symptoms, side effects, and interactions here.