Vitamin and Mineral Deficiencies: Symptoms and How to Check
Unexplained fatigue, hair loss, numb hands, frequent colds — all of these can simply be symptoms of specific deficiencies. Not rare or exotic ones. Vitamin D, iron, B12, and magnesium deficiencies are ordinary occurrences for people living at northern latitudes, vegetarians, office workers, and anyone who rarely gets outdoors. This article covers what deficiencies affect wellbeing, how to test for them, and what counts as a normal result.
Vitamin D deficiency: the most common deficiency
Vitamin D is not just "the bone vitamin". It plays a role in immune function, nervous system health, inflammation regulation, and even mood. Vitamin D receptors have been found in virtually every tissue in the body.
Research shows that vitamin D deficiency (below 20 ng/mL) affects 40–80% of the population — especially during autumn and winter, and in people who spend little time outdoors.
Symptoms of vitamin D deficiency:
- chronic fatigue and muscle weakness;
- frequent infections, impaired immunity;
- bone pain, especially in the back, hips, and legs;
- low mood, apathy;
- reduced cognitive function, "brain fog";
- slow wound healing.
25(OH)D reference ranges:
- severe deficiency — below 10 ng/mL (25 nmol/L);
- deficiency — 10–20 ng/mL (25–50 nmol/L);
- insufficiency — 20–30 ng/mL (50–75 nmol/L);
- normal — 30–100 ng/mL (75–250 nmol/L); optimal — 40–60 ng/mL;
- excess (toxic level) — above 100 ng/mL.
Deficiency is typically corrected with vitamin D3 (cholecalciferol) supplements. The dose is determined by a doctor based on baseline levels. Taking high doses (above 4,000 IU per day) without monitoring blood levels is not recommended — vitamin D is fat-soluble and accumulates in the body with excessive intake.
Iron and ferritin deficiency
Iron is essential for making haemoglobin — the protein that carries oxygen to cells. When iron is depleted, cells are effectively starved of oxygen.
Iron deficiency is the most widespread nutritional deficiency in the world. According to the WHO, about 30% of the global population is affected. Most vulnerable groups: women of reproductive age, pregnant women, vegetarians, children during growth spurts, people with gastrointestinal conditions.
Symptoms of iron deficiency and anaemia:
- fatigue and weakness — the most common symptom;
- pale skin and mucous membranes;
- shortness of breath with mild exertion;
- rapid heartbeat;
- hair loss, brittle nails;
- restless legs syndrome (uncomfortable sensations in the legs at night);
- cravings for non-food items — chalk, ice, starch (pica syndrome);
- poor concentration and memory.
Reference values:
- Ferritin: men — 30–300 µg/L; women — 15–150 µg/L. Most specialists recommend at least 50–70 µg/L for good wellbeing. Ferritin below 30 µg/L is clear deficiency.
- Haemoglobin: men — 130–170 g/L; women — 120–150 g/L. Below these thresholds indicates anaemia requiring treatment.
- Serum iron: normal — 11–30 µmol/L. Less informative than ferritin alone.
- TIBC (total iron-binding capacity): normal — 45–80 µmol/L. Elevated in iron deficiency.
Important: before starting iron supplements, the cause of the deficiency should be identified. In an adult man or a postmenopausal woman, iron deficiency without an obvious reason is grounds to rule out hidden bleeding (gastrointestinal, oncological).
Vitamin B12: symptoms and at-risk groups
Vitamin B12 is involved in DNA synthesis, red blood cell production, and nervous system function. The body cannot produce it — it comes exclusively from animal foods (meat, fish, eggs, dairy).
Groups at risk for B12 deficiency:
- vegetarians and vegans — the primary at-risk group;
- older adults (over 60) — the stomach produces less intrinsic factor needed for B12 absorption;
- people taking metformin (for diabetes) — the drug impairs B12 absorption;
- long-term users of proton pump inhibitors (omeprazole and similar);
- people with GI conditions — Crohn's disease, gastric resection, atrophic gastritis.
Symptoms of B12 deficiency:
- fatigue and weakness;
- numbness and tingling in the hands and feet;
- impaired coordination, unsteady gait;
- memory problems and cognitive decline;
- depression, irritability;
- inflamed, smooth "beefy" tongue (glossitis);
- megaloblastic anaemia — enlarged red blood cells.
Reference range: serum B12 — 200–900 pg/mL (148–664 pmol/L). Deficiency: below 200 pg/mL. A suboptimal level (200–300 pg/mL) can already cause neurological symptoms.
Magnesium and its role
Magnesium participates in over 300 biochemical reactions: protein synthesis, energy production, muscle and nerve function, blood sugar regulation, and blood pressure control. It is one of the body's most actively used minerals.
Symptoms of magnesium deficiency:
- muscle cramps and twitches, especially in the calves;
- chronic fatigue;
- sleep difficulties — trouble falling asleep, light sleep;
- irritability, anxiety;
- headaches and migraines;
- rapid heartbeat, palpitations;
- constipation.
Serum magnesium range: 0.7–1.1 mmol/L. However, serum levels reflect total body magnesium poorly — most magnesium is inside cells, not in the blood. Normal lab results don't rule out deficiency. Clinical symptoms matter more here.
Food sources of magnesium: nuts (especially almonds and cashews), pumpkin seeds, dark chocolate, legumes, leafy greens. Among supplements, magnesium citrate, glycinate, and malate absorb better than magnesium oxide.
How to properly check for deficiencies (tests and reference values)
A basic panel for assessing the main deficiencies:
- 25(OH)D — vitamin D; normal 30–100 ng/mL; optimal 40–60 ng/mL;
- Ferritin — iron stores; at least 50–70 µg/L for good wellbeing;
- Complete blood count with reticulocytes — anaemia;
- Vitamin B12 — normal 200–900 pg/mL;
- Serum magnesium — normal 0.7–1.1 mmol/L (note its limited reliability);
- Serum zinc — normal 11–18 µmol/L (for frequent infections, skin problems);
- Folate — especially important during pregnancy and when taking methotrexate.
Timing: ferritin, serum iron, and CBC can be taken at any time. Vitamin D and B12 also have no special requirements. Serum magnesium is best taken in the morning, fasting.
Not sure where to start? Try describing your symptoms to the assistant — it will help identify which tests to prioritise and which doctor to see.
Frequently asked questions
Can I take all vitamins at once without testing?
Multivitamins at preventive doses are relatively safe, but they're often not enough to correct a real deficiency — therapeutic doses are higher. Fat-soluble vitamins (A, D, E, K) accumulate in the body and can be toxic with prolonged high-dose use. Testing first is the better approach.
How long before vitamin D supplementation improves how I feel?
With significant deficiency, most people notice improvement in energy and mood within 4–8 weeks of regular supplementation. Recheck vitamin D levels after 2–3 months to evaluate the result and adjust the dose.
Can B12 deficiency be corrected through diet alone?
With mild reduction — yes, by resuming animal food intake. With significant deficiency, especially when neurological symptoms are present, supplements are needed — oral tablets or injections. Injections are used when intestinal absorption is impaired.
My tests are normal, but I'm still tired. Why?
Laboratory reference ranges reflect population averages and may not align with your personal optimum. Also, not all deficiencies show up in standard tests. If baseline markers are normal, consider other causes: sleep disorders, hormonal imbalance, or psychological factors.
Should I take vitamin D in summer too?
If you regularly spend time in direct sun between 10 am and 3 pm (at least 15–30 minutes a day with arms and legs exposed), summer sun may be enough. But most city-dwellers produce less vitamin D than they assume. The practical approach: test at the end of summer and decide based on the result.
Symptomatica is an informational reference service. Not a medical service; does not diagnose or prescribe treatment. For any symptoms, please consult a doctor.