Every mineral in your body — every atom of zinc, selenium, iodine, or the raw materials your liver uses to make choline — started somewhere in the ground. Plants can't manufacture minerals the way they photosynthesise sugar from sunlight; they can only draw up whatever is already present in the soil around their roots. Animals then eat those plants (or eat other animals that ate those plants), and we eat both. If the soil is depleted, the plant is depleted, the animal is depleted, and so are we.
In America, soil is often casually called "dirt" — something to be washed off, swept away, kept outside. That word choice reveals a real disconnect: we are, quite literally, built from the minerals found in the earth. Every bone, hormone, enzyme, and thyroid cell in your body depends on minerals that started as soil, taken up by a plant, and passed along the food chain until it reached your plate. Treat that soil as depleted, sterile "dirt," and the food grown in it comes up short too — and so, eventually, do we. Without those minerals, the result isn't abstract: it's measurable deficiency, and the health issues that follow from it.
It's worth pausing on this, because it's often dismissed with a shrug. But soil isn't an inert backdrop to farming; it's a living, mineral-rich foundation that quite literally built every nutrient in the food on your plate. Decades of intensive farming, monocropping, and reduced crop rotation have measurably lowered the mineral density of soil in many parts of the world — which is part of why two of the minerals below (selenium and iodine) are now recognised as commonly low in Irish diets specifically, regardless of how "healthy" someone's food choices look on paper.
Let's go through four minerals that matter enormously and are easy to under-consume: choline, zinc, selenium, and iodine.
Choline — for your brain
Choline is the raw material your body uses to build acetylcholine, a neurotransmitter central to memory, focus, and muscle control. It's also a structural component of the phospholipids that make up your cell membranes — including in the brain — and it plays a critical role in fetal brain development during pregnancy.
Food sources: egg yolks, liver, beef, chicken, salmon, soybeans, wheat germ, quinoa, broccoli and Brussels sprouts.
Reference intake: the UK/Ireland RNI system doesn't set a formal RNI for choline, but the European Food Safety Authority (EFSA) sets an Adequate Intake of 400mg/day for adults, rising to 480mg in pregnancy and 520mg during breastfeeding.
What that looks like in food: three whole eggs (roughly 440mg) covers the entire day's target on their own. A 100g portion of beef liver (around 356mg) gets you almost all the way there too.
Low intake has been linked to: poor memory and concentration ("brain fog"), and — because the liver relies on choline to export fat properly — a build-up of fat in the liver over time.
Zinc — for fertility and immunity
Zinc is involved in over 300 enzyme reactions in the body, but two areas stand out: immune defence and reproductive health. It's essential for sperm production and testosterone synthesis in men, and plays a role in ovulation and egg quality in women. It's also required for the immune cells that fight off everyday infections.
Food sources: oysters and other shellfish, red meat, pumpkin seeds, cashews, chickpeas, lentils, eggs, dairy.
Reference intake (UK RNI): 9.5mg/day for men, 7mg/day for women.
What that looks like in food: a 100g beef steak (around 5mg) plus a small handful of pumpkin seeds (30g, around 2mg) gets you close to the full target for women and most of the way for men. Oysters are in a different league entirely — six oysters provide roughly 32mg, several times the daily target in one go.
Low intake has been linked to: frequent colds and infections, slow wound healing, and reduced fertility in both sexes.
Selenium — for immunity (and your thyroid)
Selenium is a powerful antioxidant mineral and a key cofactor for the enzymes that convert inactive thyroid hormone (T4) into its active form (T3) — so a selenium shortfall doesn't just affect immunity, it can compound an existing thyroid problem.
Food sources: Brazil nuts (by far the richest source), seafood, organ meats, eggs, sunflower seeds.
Reference intake (UK RNI): 75µg/day for men, 60µg/day for women.
What that looks like in food: just one to two Brazil nuts (roughly 68–95µg each) covers the entire day's requirement on their own — a 100g portion of tinned tuna (around 92µg) does the same job.
Worth noting for anyone in Ireland specifically: Irish soil is naturally low in selenium, so even a varied, "good" diet here can fall short unless selenium-rich foods are deliberately included.
Low intake has been linked to: weakened immune response, muscle weakness and fatigue, and reduced conversion of thyroid hormone into its active form.
Iodine — for your thyroid
Iodine is the mineral your thyroid gland uses to manufacture thyroid hormone itself — without enough of it, the thyroid physically cannot produce what your metabolism needs, regardless of how well everything else is functioning.
Food sources: fish, dairy, eggs, iodised salt (note: most salt sold in Ireland and the UK is not iodised, unlike in the US).
Reference intake (UK RNI): 140µg/day for adults.
What that looks like in food: a 100g portion of cod (around 120µg) plus a glass of milk (200ml, around 70µg) comfortably clears the daily target. A quick caution on seaweed: while it's often recommended as an iodine source, its content varies enormously by type and origin — some kelp can contain many times a safe daily amount in a single serving — so it's not a reliable way to estimate intake without knowing the specific product's iodine content.
Also worth noting: like selenium, Irish soil is naturally low in iodine, and Ireland doesn't have mandatory salt iodisation — so intake here tends to run lower than in countries where it does.
Low intake has been linked to: an enlarged thyroid gland (goitre), fatigue, weight gain, feeling the cold, and — critically — impaired neurological development in babies when a mother is deficient during pregnancy.
Why a diet high in refined food can't get you there
Refining food strips away exactly the parts of a plant where minerals are concentrated. When wheat is milled into white flour, the bran and germ — where most of the zinc, selenium, and other minerals live — are removed, leaving mostly starch behind. The same is true of white rice versus brown, or a sugary snack versus the whole food it was made from. What's left behind is calorie-dense and mineral-poor: enough energy to feel "full," but a fraction of the nutrient content.
This is the core problem with a diet built mainly around processed and refined foods — it's not usually short of calories, it's short of the minerals that came from soil, and no amount of quantity fixes that. You can eat plenty and still be running low on choline, zinc, selenium, and iodine, because the whole foods that carry them — shellfish, organ meats, nuts, seeds, whole grains, eggs — are exactly what gets left out.
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