The Minerals

TL;DR. Vitamins are organic molecules; minerals are single elements, and unlike vitamins they cannot be destroyed by cooking, only leached into the water. The deficiencies that matter globally are iron (the most common nutritional deficiency in the world, affecting roughly a quarter of humanity), iodine (whose deficiency was the leading preventable cause of intellectual disability until salt iodisation), and zinc. The excesses that matter are sodium, which raises blood pressure across whole populations, and supplemental iron and calcium, both of which can do harm when taken without need.

Key takeaways

• Iron deficiency affects about 2 billion people and is the world's most common nutritional deficiency. Absorption differs fivefold between animal (haem) and plant (non-haem) sources.
• Vitamin C dramatically increases plant iron absorption; tea, coffee, and calcium dramatically reduce it. The timing of a cup of tea genuinely matters.
• Salt iodisation is one of the highest-impact public health measures ever implemented, and iodine deficiency is quietly returning in some countries as people switch to non-iodised specialty salts and plant milks.
• Sodium reduction lowers blood pressure at population scale, and roughly 70 to 80 percent of intake comes from processed food rather than the salt cellar.
• Potassium is the mineral almost everyone under-consumes, and raising it lowers blood pressure roughly as effectively as cutting sodium.

The minerals that matter

Major minerals are needed in amounts above 100 mg a day; trace minerals below that. The distinction is about quantity, not importance: you need 1 gram of calcium a day and 150 micrograms of iodine, and running out of either is serious.

Iron: the world's commonest deficiency

In short: Two forms with very different absorption, tight regulation of uptake and no route for excretion, and a set of dietary interactions that matter more than the raw amount in the food.

Why the body is so careful with it. Iron is essential (haemoglobin, myoglobin, and dozens of enzymes) and dangerous (free iron catalyses reactions that generate damaging radicals, and bacteria need it to grow). So iron is always bound to a carrier protein, and critically the body has no mechanism for excreting excess iron. Regulation happens entirely at absorption, via the hormone hepcidin, which shuts down intestinal iron uptake when stores are high or when inflammation is present.

The two forms:

That difference is why iron intake and iron status can diverge so much between diets.

What increases non-haem absorption:

• Vitamin C. The single strongest enhancer: 50 mg with a meal can increase non-haem iron absorption by three- to sixfold, by reducing ferric iron to the absorbable ferrous form. Practically: a glass of orange juice, tomatoes, or peppers with a lentil dish.
• The "meat factor." Meat, fish, and poultry enhance absorption of non-haem iron eaten alongside them, by a mechanism still not fully explained.
• Cooking in cast iron, particularly acidic foods, genuinely adds absorbable iron.
• Fermentation, soaking, and sprouting, which degrade phytate.

What decreases it:

• Phytate in whole grains, pulses, nuts, and seeds. The strongest inhibitor. Soaking, sprouting, fermenting, and leavening bread with real sourdough all reduce it substantially.
• Polyphenols in tea, coffee, cocoa, and red wine. A cup of tea with a meal can reduce non-haem iron absorption by 60 percent or more. This is one of the most actionable facts in this chapter: if you are iron deficient, drink tea and coffee between meals, not with them.
• Calcium, which interferes with both forms. Do not take a calcium supplement with your iron supplement.
• Antacids and proton pump inhibitors, because stomach acid is needed to solubilise iron.

Deficiency is the most common nutritional deficiency worldwide. It progresses in stages: depleted stores (low ferritin, no symptoms) → iron-deficient erythropoiesis → iron deficiency anaemia (fatigue, pallor, breathlessness on exertion, poor concentration, cold intolerance, brittle nails, and sometimes pica, a craving for non-food substances such as ice, clay, or starch, which is a genuinely distinctive clinical clue).

Who is at risk: menstruating women (particularly with heavy periods), pregnant women, infants and toddlers, adolescents in growth spurts, endurance athletes (through foot-strike haemolysis and gut losses), blood donors, vegetarians and vegans, and anyone with gastrointestinal blood loss. That last one matters most: iron deficiency anaemia in a man or a postmenopausal woman requires investigation for a gastrointestinal source, because colorectal cancer presents this way. It is not something to self-treat with supplements.

Supplementation notes. Ferrous sulphate is the standard and cheapest form. Absorption is better on an empty stomach and better with vitamin C, and worse with food, tea, and calcium. Constipation and dark stools are extremely common; the dark colour is harmless. Recent evidence supports alternate-day dosing as at least as effective as daily dosing and better tolerated, because a large dose raises hepcidin and blocks absorption the following day.

Excess iron is a real danger. Haemochromatosis, a common genetic condition particularly in people of northern European ancestry (roughly 1 in 200 homozygous for the main HFE variant), causes excessive absorption and progressive damage to liver, pancreas, heart, and joints. Treatment is repeated blood removal, which is elegantly simple. And iron tablets are a leading cause of fatal poisoning in young children, because they look like sweets and the lethal dose is small. Keep them out of reach; this is a genuine and repeated paediatric emergency.

Calcium and bone

In short: 99 percent of your calcium is in bone, which also functions as the buffer that keeps blood calcium constant; dietary calcium matters, and less than the dairy marketing suggests.

Blood calcium is held in an extremely narrow range because it controls nerve and muscle function, and the body will dissolve bone to maintain it. Bone is therefore both a structure and a reservoir.

Absorption is about 25 to 35 percent of intake and requires vitamin D. It is higher when intake is low and during growth and pregnancy, and lower with age.

Non-dairy sources, since this is the common question:

Spinach is the instructive case. It is high in calcium and also high in oxalate, which binds calcium into an insoluble compound. Its calcium is almost entirely unavailable, which is why spinach's reputation as a calcium source is wrong, and why low-oxalate greens (kale, bok choy, broccoli, collards) are far better sources despite lower raw numbers.

Supplements are not the same as dietary calcium. Several analyses have associated calcium supplements, particularly at high doses without vitamin D, with a small increase in cardiovascular events, an association not seen with dietary calcium. The current position of most bodies is to meet calcium needs from food where possible and to supplement only for a documented shortfall. Supplemental calcium also raises kidney stone risk, while dietary calcium lowers it, because calcium in the gut binds oxalate and stops it being absorbed. That inversion catches people out: low-calcium diets are a risk factor for calcium oxalate stones.

Bone health is not mostly about calcium. Weight-bearing and resistance exercise, adequate protein, vitamin D, not smoking, and moderate alcohol all matter substantially. Calcium is necessary and not sufficient.

Iodine: the quiet success and the quiet backslide

In short: Needed only for thyroid hormones, deficiency in pregnancy permanently impairs brain development, and salt iodisation nearly solved it before specialty salts and plant milks started reopening the gap.

Iodine has exactly one job: it is a structural component of thyroid hormones T3 and T4, which regulate metabolic rate throughout the body and, critically, brain development in the fetus and infant.

Deficiency causes goitre (the thyroid enlarging as it strains to capture more iodine), hypothyroidism, and, in pregnancy, cretinism: irreversible intellectual disability, deaf mutism, and stunting. Milder maternal deficiency is associated with measurable reductions in child IQ, and this is the reason iodine deficiency was described by the WHO as the leading preventable cause of intellectual disability worldwide.

Salt iodisation, begun in Switzerland and the United States in the 1920s and expanded globally from the 1990s, is among the cheapest and most effective public health interventions ever undertaken. The number of iodine-deficient countries has fallen dramatically.

The backslide is worth flagging because it is current and largely unnoticed:

• Specialty salts (Himalayan pink, sea salt, kosher salt) are usually not iodised. Switching from table salt to sea salt for perceived health reasons removes an iodine source while delivering the same sodium.
• Plant milks are often not fortified with iodine, whereas dairy milk is a major iodine source in countries like the UK (via iodophor teat disinfectants and fortified cattle feed). People switching from cow's milk to almond or oat milk can lose a substantial share of their iodine intake without realising it.
• Reduced salt intake for cardiovascular reasons reduces iodine intake where salt is the vehicle.

The UK, in particular, has documented mild iodine deficiency in teenage girls and pregnant women, which matters given the pregnancy stakes.

Excess iodine is also harmful, causing thyroid dysfunction in both directions. The main route is seaweed: kelp (kombu) is extraordinarily high in iodine, and regular consumption or kelp supplements can deliver many times the upper limit. Nori is far lower and fine.

Sodium and potassium: the pair

In short: They work as opposing partners, most people eat too much sodium and too little potassium, and the ratio may matter more than either number.

Sodium

Essential in small amounts, and the physiological requirement is roughly 500 mg a day. Actual intakes average 3,000 to 5,000 mg in most countries, against WHO advice of under 2,000 mg (about 5 g of salt).

Sodium and blood pressure is one of the better-evidenced relationships in nutrition. The DASH-Sodium trial, which fed participants controlled diets at three sodium levels, showed a clear dose-response reduction in blood pressure. Meta-analyses of trials show reducing sodium lowers blood pressure, more in people who are hypertensive and salt-sensitive. Population studies of countries that reduced salt supply, notably Finland's decades-long programme, show corresponding falls in stroke and heart disease.

The nuance, since it is often used to dismiss the whole thing: some cohort studies find a J-shaped curve where very low sodium is also associated with higher mortality. Interpretation is contested, with reverse causation (sick people are advised to cut salt) and measurement error from single spot urine samples as the main critiques. The mainstream position, that most populations eat far more sodium than they need and reducing it lowers blood pressure, survives this challenge.

Where the salt actually is: roughly 70 to 80 percent of sodium intake in industrialised countries comes from processed and restaurant food, not from the salt cellar. Bread is frequently the single largest contributor, not because it is very salty but because of how much is eaten. So the effective interventions are reformulation by manufacturers and cooking from raw ingredients, not moving the salt shaker off the table.

Salt substitutes, replacing part of the sodium chloride with potassium chloride, tackle both sides at once. The large SSaSS trial in rural China found a substituted salt reduced stroke, cardiovascular events, and total mortality. That is a strong result for a very cheap intervention. The caution is that people with advanced kidney disease or on potassium-sparing drugs must not use them, because they cannot excrete the potassium load.

Potassium

Almost everyone eats too little. Recommended intakes are 3,500 to 4,700 mg a day; typical intakes are well under 3,000 mg. It is the mineral most reliably associated with lower blood pressure across trials, and raising potassium intake appears roughly as effective as cutting sodium.

Best sources are not bananas, which are famous and only moderate. Per typical serving: potatoes with skin, beans and lentils, dried apricots, spinach and other greens, avocado, tomato and tomato products, yoghurt, and salmon all deliver more.

The sodium-to-potassium ratio predicts cardiovascular outcomes better than either alone in several analyses, which conveniently points at the same advice from two directions: less processed food, more vegetables and pulses.

Zinc, selenium, magnesium, and the rest

Zinc. A cofactor in hundreds of enzymes and in the zinc-finger proteins that regulate gene expression. Deficiency causes impaired immunity, poor wound healing, hair loss, skin lesions, growth failure in children, and loss of taste and smell. It is common in low-income settings and in diets high in phytate, which binds zinc as it does iron. Zinc supplementation reduces the duration and severity of childhood diarrhoea substantially and is a WHO-recommended treatment. Zinc lozenges for colds have modest evidence for shortening duration, at high doses started within 24 hours, with an unpleasant taste and nausea as common costs. Chronic high-dose zinc causes copper deficiency, which can produce anaemia and neurological problems, so long-term supplementation above the upper limit of 40 mg is a bad idea. Intranasal zinc products caused permanent loss of smell in some users and were withdrawn.

Selenium. Part of the glutathione peroxidase enzymes and of the enzymes that activate thyroid hormone. Soil selenium varies enormously by region, so intake follows geography: Keshan disease, a cardiomyopathy, occurred in selenium-poor regions of China. The window between adequate and excessive is narrower than for most minerals. Brazil nuts are extraordinarily selenium-dense, with a single nut potentially supplying an entire day's requirement or more, and eating a handful daily can cause selenosis: hair loss, brittle nails, garlic breath, and neurological symptoms. One or two Brazil nuts a day is a sensible supplement; ten is not.

Magnesium. Involved in over 300 enzyme systems, in ATP function (ATP is biologically active as a magnesium complex), and in muscle and nerve function. Intakes are commonly below recommendations, particularly on diets low in whole grains, nuts, and greens. Deficiency associations with hypertension, type 2 diabetes, and arrhythmia are consistent observationally; supplement trials show small blood pressure reductions. The popular use for leg cramps has weak evidence. Different salts differ in absorption and in laxative effect: magnesium oxide is poorly absorbed and mostly a laxative; citrate, glycinate, and malate are better absorbed.

Fluoride. Incorporates into tooth enamel as fluorapatite, which is more acid-resistant. Water fluoridation and fluoride toothpaste both reduce dental caries substantially, and the topical effect from toothpaste is now understood to be the more important mechanism. Excess during tooth development causes dental fluorosis, usually mild white flecking, which is why children should use a smear rather than a strip of toothpaste. Very high chronic intakes, as occur naturally in parts of India and East Africa, cause skeletal fluorosis. The safety debate about community water fluoridation at standard concentrations has been extensively reviewed; recent attention to possible neurodevelopmental effects concerns concentrations well above those used in fluoridated supplies, and the interpretation is contested.

Copper, manganese, chromium, molybdenum. Deficiencies are rare in ordinary diets. Chromium supplements are widely sold for blood sugar control and the evidence is weak and inconsistent.

The bottom line

• Minerals are elements: indestructible by cooking, only leached into water. Use the cooking liquid where you can.
• Iron is the world's commonest deficiency. Plant iron absorption swings by several-fold depending on what you drink and eat with it, and vitamin C up, tea and coffee down, are the two biggest levers.
• Unexplained iron deficiency in men and postmenopausal women needs investigating rather than supplementing.
• Calcium from low-oxalate greens and fortified foods is as usable as dairy calcium; spinach calcium is not. Supplements are a weaker option than food.
• Iodine is a solved problem quietly reopening, via non-iodised specialty salts and unfortified plant milks. It matters most in pregnancy.
• Most people eat too much sodium and too little potassium, and most of the sodium is already in the food when they buy it.

Sources and notes

Requirements and upper limits follow the same DRI, EFSA, and SACN sources as Chapter 15. Iron absorption enhancers and inhibitors, including the tea and polyphenol effect, follow Hallberg's and Hurrell's work; alternate-day iron dosing follows Stoffel et al., The Lancet Haematology, 2017. Hepcidin regulation follows Ganz's reviews. Calcium absorption fractions by food follow Weaver and Heaney's measurements. Calcium supplements and cardiovascular risk follow Bolland et al., BMJ, 2010, and its contested replies. Iodine deficiency as a preventable cause of intellectual disability follows WHO and Iodine Global Network reporting; UK iodine insufficiency in adolescents follows Vanderpump et al., The Lancet, 2011. Sodium and blood pressure follows DASH-Sodium (Sacks et al., NEJM, 2001) and the Cochrane reviews; the salt substitute trial is SSaSS, Neal et al., NEJM, 2021. The J-curve controversy follows PURE (Mente et al.) and its methodological critiques. Selenium geography and selenosis follow Rayman's reviews. Zinc for colds follows Cochrane reviews and Hemila's analyses. Fluoride follows the Cochrane water fluoridation review and Public Health England assessments.

Open questions. The sodium J-curve is genuinely contested and turns almost entirely on whether spot urine estimation is adequate, which is a methodological argument rather than a biological one. Recent attention to fluoride and neurodevelopment concerns concentrations above those used in fluoridated supplies, and its interpretation is disputed.

👉 Next: the phytochemicals, where the gap between what plants contain and what the marketing claims is at its widest.