Vitamin deficiency symptoms: what each one feels like, and the test that confirms it

Tiredness, tingling, a sore tongue and cramps each point to a short list of nutrients, and a blood test for the right nutrient is what confirms a deficiency. The table below matches each complaint to its likely nutrients and the tests a doctor may check, and five traps follow that can make a real deficiency look normal.

Vitamin deficiency symptoms: the short answer

A vitamin deficiency means the body has less of a nutrient than it needs to do its work. It happens in four ways: too little of the nutrient in the diet, a gut that fails to absorb it, a need that rises (pregnancy, blood loss, growth), or a medicine that blocks it. Most of the symptoms are non-specific, meaning the same tiredness or brain fog comes just as easily from short sleep, stress, an underactive thyroid or low iron. So symptoms narrow the list of suspects, and only the right blood test, read with its traps in mind, confirms a deficiency.

Deficiencies are also less common than supplement marketing suggests. When the CDC measured nutrients directly in the blood of a large, representative sample of Americans, a handful came up often and the rest were rare ¹:

Folate deficiency became uncommon in the US after grain products were fortified with folic acid in 1998. Minerals sit alongside vitamins on this page because people who search for a vitamin deficiency usually mean iron, magnesium and zinc as well.

Start from what you feel

Find your symptom in the left column. The middle column lists the nutrients that can cause it, commonest first, and the right column names the tests a doctor may use to check. 25-OH vitamin D is the standard vitamin D test, MMA (methylmalonic acid) is a backup check for B12, transferrin saturation shows how much iron is moving in your blood, and PT/INR is a clotting-time test.

Two symptoms that point to the same nutrient make the link stronger than one. A sore tongue together with tingling feet points toward B12 far more than either symptom does on its own. To use the table, take your symptoms and the matching tests to your doctor, for example: "I have tingling feet and a sore tongue; could we check B12, with MMA if it is borderline, and a full blood count?"

Bruising you cannot explain, or bleeding that is hard to stop, needs a doctor and a blood count first, because a platelet or blood disorder is a more urgent cause than a vitamin.

The deficiencies worth knowing well

Vitamin D

Low vitamin D causes bone pain, aching muscles and weakness around the hips and thighs (getting up from a low chair becomes harder), and over years it thins the bones. People with depression often have low vitamin D, but trials giving vitamin D for depression have produced mixed results. The Institute of Medicine's 2011 report set vitamin D deficiency at a 25-hydroxyvitamin D (25-OH vitamin D) below 12 ng/mL (30 nmol/L) and called 20 ng/mL (50 nmol/L) enough for bone health in nearly everyone ². The condition itself is covered on vitamin D deficiency, and the test on 25-OH vitamin D.

Vitamin B12

B12 deficiency causes tiredness, a smooth sore tongue, tingling in the feet and hands, poor balance and trouble with memory. B12 nerve damage can start before any anemia shows on a blood count. In John Lindenbaum's 1988 series of 141 patients with nerve or mental symptoms caused by B12 deficiency, 40 of them had no anemia and red cells of normal size ³.

B12 occurs naturally only in animal foods, so vegans need fortified foods or a supplement ⁴. Many older adults absorb less because atrophic gastritis reduces stomach acid, and long-term metformin or acid-blocking medicines (proton pump inhibitors, or PPIs) lower B12 over time ⁴. In a 2013 JAMA study, two or more years of PPI use carried 65% higher odds of a new B12 deficiency ⁵, and periodic B12 checks are advised for people on long-term metformin ⁴. Gut surgery and pernicious anemia, an autoimmune condition that blocks B12 absorption, round out the list; B12 deficiency covers treatment.

Folate

Folate deficiency causes anemia (too few red blood cells) with large red cells, tiredness, mouth sores and a sore tongue. Folate matters most around conception, because low folate in early pregnancy raises the risk of neural tube defects such as spina bifida; the US Preventive Services Task Force recommends that anyone who could become pregnant take a daily folic acid supplement ⁶, and the right product is a question for a doctor or pharmacist. Heavy drinking and some anticonvulsant medicines also lower folate. See folate deficiency.

Iron

Iron deficiency causes tiredness, pale skin, breathlessness, restless legs, hair shedding, feeling cold and sometimes a craving to chew ice. It is commonest in women with heavy periods, in pregnancy, in frequent blood donors and in people who eat no meat. In men and in women past menopause, iron deficiency is a sign to look for blood loss, often from the gut. Ferritin, the protein that stores iron, is the first test; the WHO defines iron deficiency in healthy adults as a ferritin below 15 µg/L ⁷. See iron deficiency and iron studies explained.

Magnesium, zinc, iodine and copper

Low magnesium causes muscle cramps, eyelid twitches and palpitations, and turns up with diuretics, long-term PPIs, heavy drinking and poorly controlled diabetes; see magnesium deficiency. Low zinc dulls taste and smell, slows wound healing, thins hair and makes infections more frequent; see zinc deficiency.

Low iodine (in vegans, people who avoid iodised salt and dairy, and in pregnancy) can swell the thyroid and cause tiredness, feeling cold and weight gain; it is checked with a urine iodine test and thyroid tests, not a standard blood panel. Low copper, seen after bariatric surgery or with long-term high-dose zinc, causes anemia, low white cells and nerve damage that looks like B12 deficiency.

Vitamins C, A, E, K and thiamine: rare, with classic signs

Scurvy, from vitamin C deficiency, appears after weeks to months of eating almost no fruit or vegetables, with fatigue, swollen bleeding gums, easy bruising and wounds that will not heal; it still turns up in very restrictive diets, heavy drinkers and older people living alone. Vitamin A deficiency shows first as night blindness and is a leading preventable cause of childhood blindness worldwide. Vitamin E deficiency is rare and seen with fat malabsorption (cystic fibrosis, cholestatic liver disease); it causes nerve damage, an unsteady walk and muscle weakness. Vitamin K deficiency causes bleeding and bruising, mostly in newborns and people with fat malabsorption. Thiamine (B1) deficiency is the one to fear in heavy alcohol use: Wernicke encephalopathy brings confusion, an unsteady walk and abnormal eye movements, and many patients do not show all three, so it is easily missed.

Who is most likely to be low

Which blood tests confirm it, and the traps

Each nutrient has a best first test. The cutoffs below are the ones most US labs and guidelines use, in both common units; your own lab's reference range sits beside your result. Transferrin saturation is the share of the blood's iron carrier that is loaded with iron, and RBC folate is folate measured inside red cells.

A complete blood count adds a clue. Large red cells (high MCV) lean toward B12 or folate, and small red cells (low MCV) lean toward iron. Low B12, low folate and, less often, low copper can also lower the white cell and platelet counts, so an unexplained low white count is a reason to check them; the CBC guide explains the rest of the count.

CalculatorVitamin D converterVitamin D comes back in ng/mL in the US and nmol/L almost everywhere else; convert yours before comparing it to a cutoff.Work it out

Five traps that hide a real deficiency

1. Serum B12 can sit in the grey zone while the tissues are short. Methylmalonic acid (MMA), a by-product that builds up when cells lack B12, rises in true deficiency, and so does homocysteine ⁴. NICE's 2024 B12 guideline advises an active B12 or MMA test when a result is indeterminate and the symptoms fit ⁸.
2. Folic acid can mask B12 deficiency. Folic acid corrects the anemia of B12 deficiency while the nerve damage carries on, which is why B12 should be checked before anyone treats a large-cell anemia with folic acid alone ⁴.
3. Ferritin rises with inflammation. Because ferritin climbs during infection or inflammation, the WHO uses a cutoff of 70 µg/L instead of 15 in people with inflammation ⁷, so a ferritin of 40 during a flare can still mean low iron. If your ferritin and iron numbers seem to disagree, ferritin vs iron explains which to trust.
4. Serum magnesium sees less than 1% of the body's magnesium ⁹, so a normal serum magnesium can miss low total-body stores. An RBC magnesium (magnesium measured inside red cells) is sometimes added, though it is not standardized and no single test reliably shows total-body magnesium ⁹.
5. Supplements distort results. A dose taken in the days before a test can lift a low reading, and high-dose biotin (often in hair and nail supplements) can throw off many lab tests, including thyroid and heart tests, a problem the US FDA has warned about ¹⁰. Ask your doctor whether to pause supplements before the draw; preparing for a blood test covers the rest.

Testing can also be overdone. The Endocrine Society's 2024 guideline suggests against routine 25-OH vitamin D testing in healthy adults who have no specific reason for it ¹¹. A symptom, a risk group from the table above, or a medicine known to lower a nutrient is a reason; general curiosity usually is not. For which panels make sense in which situations, see what blood tests should I get.

When to get help quickly

• Go to an emergency department or call 911 if tiredness comes with chest pain, fainting or breathlessness at rest.
• Black, tarry stools or vomiting blood need emergency care the same day.
• Someone who drinks heavily and becomes confused or unsteady needs emergency care the same day; thiamine deficiency is an emergency.
• See a doctor within days if you have numbness, weakness or an unsteady walk; B12 nerve damage can become permanent.
• See a doctor promptly if tiredness comes with breathlessness on exertion or a racing heart.
• See a doctor promptly if bleeding gums come with bruising you cannot explain, or bleeding is hard to stop.
• See a doctor promptly if you notice new night blindness.
• See a doctor promptly if you are pregnant and have any of these symptoms.
• See a doctor promptly if iron deficiency comes with weight loss, a change in bowel habit or blood in the stool; the cause needs finding.

What to do if a test shows you're low

Find the cause before topping up. Iron deficiency in a man or a woman past menopause needs a search for blood loss; B12 deficiency from poor absorption (pernicious anemia, gut surgery) usually needs a different route than B12 from a low-meat diet, and your doctor will decide between tablets and injections. If a medicine you take lowers a nutrient, raise it with the prescriber; do not stop or change the medicine on your own, since the medicine usually matters more than the nutrient and the fix is often just monitoring or a supplement.

Food first where it is realistic: iron-rich foods can lift a mildly low ferritin, and oily fish and fortified foods add vitamin D. When your doctor advises a supplement, it should match the nutrient the test found low; a general multivitamin is rarely enough to correct a confirmed deficiency. Levels take time to recover, and doctors commonly retest vitamin D and ferritin after about three months. High doses of the fat-soluble vitamins A and D build up in the body, and long-term high-dose B6 causes the same tingling in the hands and feet that people take it for. Supplements explained covers how to judge a product.

Supplements with evidence for a confirmed deficiency

Strongest evidenceVitamin DRaises 25-OH vitamin D reliably in people who are low; benefit beyond bone health in people who are not low is unprovenIn our shop

Strongest evidenceVitamin B12Oral B12 corrects low levels in most people, including many with absorption problems when taken under medical guidance; deficiency with nerve symptoms is usually treated with injections first, so it needs a doctorIn our shop

Strongest evidenceIronRestores ferritin and hemoglobin in confirmed iron deficiency when taken under a doctor's guidance; gut side effects are common and the cause of the loss still needs findingIn our shop

Strongest evidenceFolateFolic acid taken before and in early pregnancy lowers the risk of neural tube defects; B12 should be checked before treating anemia with it

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