Chapter 14 — Key Takeaways
One page. The ferritin section alone is worth the chapter.
Why Minerals Differ from Vitamins
They're elements — they can't be destroyed, only leached. Which means:
- Absorption is where the action is, and it's tightly regulated
- Minerals compete with each other — zinc/copper, calcium/iron, iron/zinc
- The deficiency-to-toxicity window is narrower
- "It'll just be excreted" is much less true
Iron — the big one
| Heme | Non-heme | |
|---|---|---|
| Sources | Meat, poultry, fish | Plants, eggs, dairy, fortified, supplements |
| Absorbed | 15–35% | 2–20% |
| Modified by other foods | Little | Substantially |
Enhancers: vitamin C · meat/fish · acidity · soaking, sprouting, fermenting Inhibitors: phytate · tea and coffee polyphenols (large effect) · calcium · some fibers
Hepcidin regulates absorption; ⚠️ there is no excretion route. Inflammation raises hepcidin → suppressed absorption (and hard training does this for hours).
📊 The staircase
Stores full → ferritin falls (months–years, hemoglobin still normal) → hemoglobin drifts down → anemia.
Hemoglobin is a floor sensor, not an early warning system. It tells you that you've already descended three steps. Only ferritin tells you which step you're on.
Thresholds: WHO ~15 ng/mL depleted; many clinicians use <30; athletes sometimes higher. Devi was 11 with a hemoglobin of 12.6.
⚠️ Ferritin is an acute phase reactant — normal or high doesn't exclude deficiency in the inflamed. Measure CRP alongside.
⚠️ Unexplained iron deficiency in a man or post-menopausal woman = investigate for bleeding. Iron deficiency is a finding, not a diagnosis.
At risk: menstruating women · endurance athletes (especially female) · vegetarians/vegans (~1.8× requirement) · pregnancy · infants · frequent donors · GI blood loss.
The Rest, Briefly
| Mineral | The point |
|---|---|
| Calcium | Blood calcium is defended by PTH pulling from bone, so serum tells you nothing about nutrition. Supplements move density slightly, fractures barely. Protein + resistance training do more. |
| Magnesium | ⚠️ Serum is a poor marker (~1% is in blood). Real intake shortfalls vs RDA; modest BP effect; cramps generally null. Cheap, low-risk, oversold. |
| Zinc | UL ~40 mg. ⚠️ Chronic excess → copper deficiency: anemia, neutropenia, potentially irreversible neurological damage. (Walt: 50 mg, indefinitely.) ⚠️ Never intranasal. |
| Selenium | Requirement ~55 µg, UL ~400 µg — one of the narrowest windows of any nutrient. ⚠️ Brazil nuts are extremely and variably high — a daily handful is genuinely inadvisable. |
| Iodine | See below — the victory and the returning problem. |
| Potassium | AI ~2,600–3,400 mg; most people get half to two-thirds. Lowers BP. ⚠️ Supplements and potassium salt substitutes are dangerous in kidney disease or on ACE inhibitors/ARBs. |
| Sodium | See below — the most contested number in nutrition. |
Iodine: victory, and erosion
The victory: salt iodization, from the 1920s. Endemic goitre largely eliminated; cretinism became rare. The world's leading preventable cause of intellectual disability, largely solved, at almost no cost, with no behaviour change required.
The erosion — four trends, no decision: 1. Specialty salts (sea, pink, kosher, Celtic) are generally not iodized 2. ~70–75% of dietary salt is in processed food, made with non-iodized salt 3. Dairy consumption fell — and dairy is a major iodine source 4. Plant milks are frequently not fortified with iodine (though they are with calcium, D and B12)
Result: mild-to-moderate insufficiency re-emerging, concentrated in women of childbearing age — i.e. the health-conscious profile of pink salt + oat milk + plant-forward eating.
⚠️ If pregnant or planning: check the prenatal contains iodine. Not all do.
Sodium: what's disputed and what isn't
Not disputed: sodium raises blood pressure; reducing it lowers blood pressure (DASH-Sodium, dose-dependent); blood pressure causes cardiovascular disease; most people eat far more than they need (~3,000–4,000 mg; Theo 4,100), and ~70–75% comes from processed and restaurant food, not the shaker.
Disputed: whether population-level reduction reduces events, and whether there's a lower bound. PURE and similar report J-shaped associations — but rest substantially on spot urine estimation (contested method) and face reverse causation (sick people eat less), structurally identical to Chapter 12's sick-quitter bias.
Defensible position: ✅ reduce if you have hypertension or elevated blood pressure. For normotensive people the population targets are more confident than the trial evidence supports — and raising potassium may matter as much as lowering sodium.
Verdict Summary
| Claim | Verdict | Why |
|---|---|---|
| Iron supplementation helps the iron-deficient, including without anemia | ✅ Well supported | RCTs in non-anemic deficient women (fatigue) and athletes (performance). ⚠️ Test ferritin — don't guess. |
| Iodine adequacy in pregnancy matters for neurodevelopment | ✅ Well supported | Unambiguous for severe deficiency; requirement genuinely elevated (~220 vs 150 µg); harm irreversible |
| Calcium supplements prevent fractures in healthy adults | 🟠 Probably false | Density moves, fractures mostly don't. 🟢 in frail/institutionalized with vitamin D, or genuinely low intake |
| Almost everyone is magnesium deficient; supplements fix sleep, anxiety, cramps | 🟡 Unclear | Modest BP effect; cramps null; poor biomarker makes it hard to disprove |
| Zinc lozenges shorten colds | 🟡 Unclear | Modest duration effect, formulation-dependent; nothing for prevention; ⚠️ never intranasal |
| Everyone should reduce sodium below 2,300 mg | 🟡 Unclear | A live scientific disagreement, not a data shortage |
| Soil depletion means you need mineral supplements | 🟠 Probably false | Plants can't grow without minerals they need. Real only for selenium and iodine — which plants don't require, which is why iodized salt exists |
Absorption and Competition
| High intake of… | Impairs |
|---|---|
| Zinc | Copper — the Walt problem |
| Calcium | Iron and zinc, in the same meal |
| Iron | Zinc, at supplemental doses |
| Phytate | Iron, zinc, calcium — reduced by soaking, sprouting, fermenting, leavening |
| Tea/coffee polyphenols | Non-heme iron — large effect |
Timing matters for mineral supplements in a way it rarely does for vitamins. And the competition problem is almost entirely a supplement problem — whole foods deliver minerals in proportions that don't trigger it.
What to Actually Do
- ⚠️ Menstruating woman, endurance athlete, or vegetarian — especially two or three? Get ferritin checked. Not hemoglobin. The highest-yield action in this chapter.
- Fix absorption for free: vitamin C with iron meals · tea and coffee between meals, not with them · soak legumes.
- ⚠️ Don't take iron without testing.
- Calcium from food — and remember protein + resistance training do more for fractures.
- ⚠️ Check your salt is iodized, or that your prenatal contains iodine.
- Eat more potassium — potatoes, beans, greens, yogurt.
- Reduce sodium if you have high blood pressure. Cooking your own food does more than the shaker.
- ⚠️ Don't megadose single minerals. Zinc above the UL is the clearest supplement harm in Part III.
Worth Testing
Ferritin (with CRP) — the highest-yield mineral test by a wide margin · FBC alongside, not instead · serum magnesium rarely useful · zinc/selenium/copper only with clinical suspicion · urinary iodine is a population measure · ❌ "mineral hair analysis" is not validated — avoid.
One Thing to Remember
Devi was told three times that her bloods were normal. They were.
Her hemoglobin ran 13.1 → 12.8 → 12.6 across two years — every value inside the reference range, each read in isolation, the trend never assembled. The normal test was the wrong test, and a ferritin measurement costing almost nothing was the finding that changed her career.