Vitamins and Minerals Reference
The most important micronutrients: what they do, deficiency symptoms, and the best food sources.
TL;DR
- 01Fat-soluble vitamins (A, D, E, K) are stored in the body; water-soluble vitamins (B-complex, C) require regular dietary intake.
- 02Vitamin D, B12, iron, and magnesium are the most commonly deficient nutrients in modern diets.
- 03Whole foods provide micronutrients in bioavailable forms alongside co-factors that enhance absorption — supplements are second-best.
Tips
- 01Cooking vegetables in oil (roasting, sautéing) boosts absorption of fat-soluble nutrients like beta-carotene (pro-vitamin A) and vitamin K compared to eating them raw.
- 02A general multivitamin fills small gaps but delivers nutrients in forms and amounts that aren't always ideal. Targeted single-nutrient supplements address confirmed deficiencies more precisely.
Warnings
- 01Vitamin B12 from plant foods is largely inactive. Anyone following a vegan or strict vegetarian diet should supplement with at least 250 mcg of cyanocobalamin daily or 1,000 mcg every other day.
Fat-Soluble vs Water-Soluble Vitamins
The 13 essential vitamins divide into two groups based on how the body stores and uses them.
| Property | Fat-soluble (A, D, E, K) | Water-soluble (B1–B12, C) |
|---|---|---|
| Storage | Liver and adipose tissue; stored for weeks–months | Minimal storage; excreted in urine daily |
| Toxicity risk | Higher — excess accumulates | Lower — excess excreted (exception: B6 at mega-doses) |
| Dietary frequency needed | Regular but not necessarily daily | Daily intake recommended |
| Absorption requirement | Requires dietary fat for absorption | Absorbed directly from gut |
| Common deficiency risk | Vitamin D (widespread), A (developing world) | B12 (vegans, elderly), folate (pregnancy), B1 (alcohol use) |
Eating fat-soluble vitamins with a source of fat — even a small amount like a drizzle of olive oil — significantly improves absorption. Vitamin D absorption from supplements improves when taken with the largest meal of the day.
Key Vitamins: D, B12, C, and Folate
These four vitamins account for the majority of deficiencies seen in developed countries, making them priority targets for dietary attention.
| Vitamin | RDA / AI | Key functions | Best food sources | Deficiency signs |
|---|---|---|---|---|
| Vitamin D | 600–800 IU (15–20 mcg) | Calcium absorption, immune function, bone mineralisation | Fatty fish (600–1,000 IU/100g), egg yolks, fortified milk | Bone pain, fatigue, increased infection rate |
| Vitamin B12 | 2.4 mcg/day | Red blood cell formation, nerve myelin, DNA synthesis | Beef liver (71 mcg/100g), salmon, dairy, eggs | Megaloblastic anaemia, peripheral neuropathy, memory decline |
| Vitamin C | 75–90 mg/day | Collagen synthesis, antioxidant, iron absorption enhancer | Red bell pepper (190 mg/100g), kiwi, broccoli, citrus | Scurvy (rare): bleeding gums, poor wound healing |
| Folate (B9) | 400 mcg DFE/day (600 in pregnancy) | DNA synthesis, cell division, neural tube development | Lentils (180 mcg/100g cooked), spinach, asparagus, fortified grains | Neural tube defects (fetal), megaloblastic anaemia |
Essential Minerals: Iron, Calcium, Magnesium, Zinc
Minerals are inorganic elements required for structural (bone, teeth) and functional (enzymes, electrical signals) roles. These four are the most clinically significant for the general population.
| Mineral | RDA | Key role | Best sources | Absorption note |
|---|---|---|---|---|
| Iron | 8 mg (men); 18 mg (women 19–50); 27 mg (pregnancy) | Haemoglobin synthesis, oxygen transport | Beef (2.7 mg/100g), lentils (3.3 mg/100g cooked), fortified cereals | Heme iron (meat) 15–35% absorbed; non-heme (plant) 2–20%. Vitamin C doubles non-heme absorption |
| Calcium | 1,000–1,200 mg/day | Bone and teeth structure, muscle contraction, nerve signals | Milk 300 mg/cup, canned sardines 325 mg/100g, kale 150 mg/100g | Absorption drops above 500 mg in one dose — split across meals |
| Magnesium | 310–420 mg/day | 300+ enzyme reactions, muscle relaxation, blood glucose control | Pumpkin seeds 168 mg/28g, dark chocolate 64 mg/28g, almonds 80 mg/28g | Absorption decreases with high calcium or zinc intake |
| Zinc | 8–11 mg/day | Immune function, wound healing, protein synthesis, taste/smell | Oysters 74 mg/100g, beef 4.8 mg/100g, hemp seeds 10 mg/100g | Phytates in grains/legumes reduce absorption; soaking and sprouting helps |
Deficiency Warning Signs
Subclinical micronutrient deficiencies are widespread and often produce vague symptoms — fatigue, brain fog, and poor immunity — before reaching clinical thresholds on blood tests. Recognising patterns can prompt earlier dietary changes.
| Symptom or sign | Potential micronutrient deficiency |
|---|---|
| Fatigue, pallor, shortness of breath | Iron, B12, folate |
| Bone pain, muscle weakness | Vitamin D, calcium |
| Numbness or tingling in hands/feet | Vitamin B12, B6 |
| Cracked lips, sores at mouth corners | Riboflavin (B2), B6, iron |
| Hair loss, brittle nails | Iron, zinc, biotin |
| Frequent infections, slow healing | Vitamin C, zinc, vitamin D |
| Night blindness, dry eyes | Vitamin A |
| Muscle cramps, poor sleep | Magnesium, potassium |
These signs are suggestive, not diagnostic. A serum blood panel is required to confirm deficiency. Work with your doctor before high-dose supplementing, as excess iron and fat-soluble vitamins can cause toxicity.
When to Consider Supplements
Supplements are useful to address specific gaps — not as an insurance policy against a poor diet. Research consistently shows that isolated supplements rarely replicate the health benefits of whole foods, which deliver nutrients alongside fibre, polyphenols, and other co-factors.
- Vitamin D: Consider 1,000–2,000 IU daily if you live above 37° latitude, work indoors, or have darker skin. Blood level target: 50–100 nmol/L (20–40 ng/mL).
- B12: Recommended for all vegans and vegetarians; also for adults over 50 (stomach acid declines, reducing absorption from food).
- Iron: Only supplement if blood work confirms deficiency — excess iron is harmful and masks other causes of anaemia.
- Folate/Folic acid: 400 mcg/day recommended for all people of childbearing age who could become pregnant, ideally started one month before conception.
- Omega-3 (EPA/DHA): Algae-based supplements provide the same EPA/DHA as fish oil — the best option for vegans.
| Supplement | Who needs it | Typical dose |
|---|---|---|
| Vitamin D3 | Most people in northern climates | 1,000–2,000 IU/day |
| Vitamin B12 | Vegans, over-50s, metformin users | 250–1,000 mcg/day |
| Folate | Pre-conception and pregnancy | 400–600 mcg/day |
| Iodine | People avoiding dairy and iodised salt | 150 mcg/day |
FAQ
Vitamins A, D, E, and K are absorbed in the small intestine alongside dietary fat — without it, a significant portion passes through unabsorbed. Even a small amount of fat, like olive oil on a salad or an egg alongside vegetables, is enough to meaningfully boost uptake.
Fat-soluble vitamins (A, D, E, K) accumulate in the liver and adipose tissue, so excess intake — typically from high-dose supplements, not food — can reach toxic levels over time. Water-soluble vitamins are largely excreted in urine, though high-dose vitamin B6 (pyridoxine) is a notable exception that can cause nerve damage with prolonged megadosing.
Plant foods do not provide bioavailable B12, so vegans must rely on fortified foods (plant milks, nutritional yeast, fortified cereals) or a direct B12 supplement. A daily supplement of 25–100 mcg cyanocobalamin, or a weekly higher-dose option, is the most reliable strategy.
Plant foods contain non-heme iron, which is less bioavailable than heme iron from meat. Consuming vitamin C-rich foods (like red bell pepper or citrus) in the same meal significantly enhances non-heme iron absorption, while tea, coffee, and calcium-rich foods consumed simultaneously can inhibit it.
Vitamin D is difficult to obtain from food alone, and synthesis from sun exposure is limited by latitude, skin tone, clothing, and season. Most adults — particularly those in northern climates, with limited outdoor exposure, or with darker skin — benefit from a daily supplement of 1,000–2,000 IU, especially through autumn and winter.