Iodine: The Underrated Trace Element — and Its Sharp Edge

Iodine was a German success story: iodised salt made goitre rare. But recent surveys show the reversal — intake is falling again, partly because processed foods and bakeries use iodised salt less often, and fish and milk consumption has dropped. The institutes' conclusion: Germany again counts as a region at risk of mild iodine deficiency. Particularly affected: people who eat little or no animal produce — sea fish and dairy are the main natural sources — and everyone whose home and shopping consistently ends up with non-iodised salt.

The good news: for most people the fix is banal. Iodised salt in your own shaker, at the bakery and in products ("with iodised salt" in the ingredients), plus one or two portions of sea fish per week or regular dairy — that reaches the requirement (adults: about 200 µg/day per the DACH reference values) without any capsule. Total salt stays low — iodised salt means better salt, not more salt (see the blood pressure dossier).

Iodine is the rare example of a nutrient documented to harm in both directions: too little causes goitre and underactivity — too much can also derail the thyroid, in either direction. The review by Leung and Braverman documents the mechanisms: sudden iodine excess can trigger overactivity (especially in people with undetected hot nodules) and, in susceptible individuals, underactivity and inflammatory flares. Especially relevant for anyone with autoimmune thyroid disease: high-dose iodine is suspected of fuelling autoimmune activity — for this group the rule is: normal iodised-salt eating yes, high-dose preparations only on explicit medical instruction, and any irregularity (racing heart, weight swings, exhaustion) belongs in the practice.

The main source of uncontrolled excess is algae and kelp products: dried brown algae can contain multiples of the daily intake per gram, with enormous batch-to-batch variation. The European safety ceiling (tolerable upper intake: 600 µg/day for adults per the EFSA framework) is unproblematic with a sushi dinner — but quickly torn several times over with daily kelp capsules or algae "detox" cures. A 2026 dose-response meta-analysis confirms the pattern with a clear U-curve: both deficiency and excess raise the risk of thyroid nodules — precisely this sharp edge is what sets iodine apart from most nutrients.

• Most adults: iodised salt + normal mixed diet — no capsule. The capsule's effect with covered supply would be: none.
• Vegan and largely dairy-free eaters: a legitimate risk group (no fish, no dairy). First choice remains iodised salt consistently everywhere; a low-dose supplement (in the range of the daily requirement, NOT kelp) can be sensible — ideally after consultation, especially when B12 and co. are being managed as well.
• Planning pregnancy, pregnant, breastfeeding: increased need, official supplement recommendation — dose and supervision via the gynaecologist. A 2026 meta-analysis in pregnant women found that 200–300 µg of iodine per day lowered TSH and thyroglobulin — a study finding, not a dosing recommendation of our own; the actual dose is set exclusively by the treating practice.
• People with thyroid conditions (over-/underactivity, nodules, autoimmune disease): clarify iodine questions medically as a rule — neither fear of the iodised salt in food nor self-experiments with preparations. Both are common, both are the wrong way round.
• Athletes: no special need beyond normal supply — heavy sweating raises losses in theory; in practice consistent iodised salt covers that too.

And the diagnostic reminder from the other dossiers applies here as well: persistent exhaustion, weight and mood changes are a case for blood work (incl. TSH, iron, B12) — not for the self-diagnosis "must be iodine deficiency".