Chapter 14 — Further Reading

Real sources only. Where I'm unsure of exact details, I describe the source rather than inventing a citation.

Start here

NIH Office of Dietary Supplements fact sheets — ods.od.nih.gov. There is one for every mineral in this chapter, free, updated, in consumer and professional versions, with ULs and drug interactions stated plainly.

The iron and iodine sheets are the two to read, and the zinc sheet is worth it for the copper interaction if anyone you know takes an "immune" formulation.

USDA FoodData Central — fdc.nal.usda.gov. Mineral content of any food, including the ones that surprise people (a baked potato has roughly twice the potassium of a banana).

On iron — the most important section

On iron deficiency without anemia: search PubMed for "iron deficiency non-anemic fatigue randomized" and "iron supplementation endurance performance ferritin." The trials in non-anemic women with fatigue and in iron-deficient athletes are the evidence behind §14.2's ✅, and reading two or three shows you how the ferritin thresholds vary between studies — which is the honest uncertainty.

On hepcidin: search for reviews on hepcidin and exercise, and on hepcidin regulation of iron absorption. The finding that hard training suppresses absorption for hours afterward is genuinely practical for athletes and is rarely taught.

On dosing: there is a live and interesting literature on alternate-day versus daily oral iron, on the basis that daily dosing itself raises hepcidin and reduces fractional absorption. Search "alternate day iron supplementation absorption." Practice has been shifting.

On hemochromatosis: the NIDDK (niddk.nih.gov) and national haemochromatosis societies have good patient-facing material. ⚠️ Worth reading before anyone in your family starts iron supplements casually.

Clinical guidance: the British Society of Gastroenterology and equivalent bodies publish guidelines on investigating iron deficiency anemia — which is where §14.2's "a finding, not a diagnosis" comes from. Essential if you're clinically trained.

On iodine

The Iodine Global Network (ign.org) — the main international body tracking iodine status. Country profiles, current data, and a clear account of what universal salt iodization achieved.

On the re-emergence: search for national iodine status surveys — the UK, US (NHANES), Australia and several European countries all have published data, often with specific analysis of women of childbearing age. Reading your own country's is more useful than any summary.

On the history: the story of iodization in Switzerland and the US in the 1920s, and the subsequent global effort, is genuinely remarkable and almost entirely unknown. Search for accounts of the goitre belt and its disappearance.

On pregnancy: guidance from your national obstetric or public health body on iodine in pregnancy. ⚠️ Check whether your prenatal contains it — this is the single most actionable line in the chapter.

On calcium and bone

The Women's Health Initiative calcium and vitamin D arm, and subsequent meta-analyses of calcium supplementation and fracture risk. Read one meta-analysis and one critique — the field has genuinely moved and the disagreement about cardiovascular safety of supplements is unresolved.

And read Chapter 8's sources alongside, because the honest comparison is: protein intake and resistance training have better fracture evidence than calcium supplements do, and that comparison is almost never made explicitly.

Bone-health organizations — the International Osteoporosis Foundation, and national equivalents — publish current positions that reflect the shift toward food-first.

On magnesium

Search PubMed for "magnesium supplementation blood pressure meta-analysis" (modest, real) and "magnesium muscle cramps randomized" (generally null, including in pregnancy and older adults).

The contrast between those two literatures is instructive: the effect people buy it for has the weakest evidence, and the effect it actually has is one almost nobody buys it for.

On sodium — read both sides properly

DASH and DASH-Sodium (NEJM) — the controlled feeding trials establishing the blood pressure effect. Not seriously contested.

PURE sodium analyses (The Lancet and elsewhere) — the J-curve findings.

Then the methodological dispute, which is where the real argument is: search for the exchange over spot urine estimation of sodium intake versus 24-hour urine collection, including the Kawasaki and INTERSALT-based equations and their critics. This is unusually accessible for a methodological fight and it genuinely determines the answer.

WHO sodium guidance (who.int) for the population-target position.

For: anyone who has been told this is settled — in either direction.

On potassium

⚠️ Before anything else: if you have kidney disease or take ACE inhibitors, ARBs, or potassium-sparing diuretics, read the guidance from your national kidney organization on potassium before changing intake or using a salt substitute. Potassium-based "low sodium" salts are a genuine hazard in these groups.

Otherwise: the DASH literature covers potassium's role in blood pressure well, and food composition data is more useful than any supplement discussion.

On the soil depletion claim

Find the historical food composition comparisons that the claim rests on — then find the methodological critiques concerning changes in analytical methods, cultivars, sampling and table construction over the period.

Then read anything on plant mineral physiology, which is the decisive point: plants cannot grow without the minerals they themselves require. Selenium and iodine are the exceptions precisely because plants don't need them — and that asymmetry is the whole answer.

A note on what to be careful with

The mineral aisle has a specific failure mode that differs from the vitamin aisle: the harms are real.

Excess water-soluble vitamins are mostly wasted money. Excess zinc causes copper deficiency. Excess iron in someone with hemochromatosis causes organ damage. Excess selenium causes selenosis. Potassium supplements in the wrong patient cause arrhythmias. Minerals compete, accumulate, and have narrower windows.

So the asymmetry that made "it can't hurt" a reasonable-if-wrong heuristic for vitamins does not transfer here.

The test that works: does the source distinguish between correcting a measured deficiency and supplementing a population? Iron with a ferritin result behind it is medicine. Iron because you're tired is a gamble with no upside if you're replete, and a real downside if you're one of the people who shouldn't have it.