Opening the Case

You’ve done everything right. You eat the spinach and the lentils. You’ve had the steak your doctor suggested. You’ve swallowed the iron pills, put up with the stomach upset, and waited. And still your blood work comes back with iron flagged low. Meanwhile, the tiredness hasn’t lifted, and you’re losing words mid-sentence in meetings.

So you do what most of us do. You try harder. More iron-rich food. A stronger supplement. Maybe you start wondering whether you’re doing something wrong.

Here’s what most people don’t know: two people can eat the exact same meal and absorb very different amounts of iron. Some of that difference is written in your genes. And sometimes, the “low iron” on your lab report isn’t really about iron at all.

This isn’t about blame. It’s about understanding what’s really happening behind the scenes, so the effort you’re already putting in actually lands.

This is Part 1 of a three-part series. Here, we’re following the iron trail: the gatekeeper that controls it, the genes that tip it too low or too high, and why anemia is a clue your brain cares about too.

Clue #1 — Meet the Gatekeeper

When iron comes back low, the usual advice is simple: eat more red meat, take an iron pill. For many people, that works. For others, it does almost nothing, and they can go years cycling through supplements and the same flagged result.

The missing piece is a hormone called hepcidin. Think of it as the gatekeeper for iron. Your liver makes it, and it decides how much iron gets let in from your gut and how much gets released from storage. When hepcidin is high, the gate closes. When it’s low, the gate opens.

Here’s where genes come in. A gene called TMPRSS6 makes a protein whose job is to keep hepcidin in check. Certain common variations in this gene mean that brake doesn’t work quite as well, so hepcidin runs higher than it should and the gate stays partly closed. A stable iron isotope study in women found that those carrying one common TMPRSS6 variant had lower blood iron and absorbed less iron from their supplements. Same food, same pill, less iron getting through.

At the far end of the spectrum, rare and more serious TMPRSS6 mutations cause a condition called iron-refractory iron deficiency anemia, where oral iron produces little or no improvement and people need iron by infusion instead. Most people with common variants aren’t in that category. But it shows how much one gene can matter.

There’s a second version of this story too. Sometimes your serum iron reads low, but your ferritin (your iron storage marker) is normal or even high. Chronic infection and inflammation also push hepcidin up, so the iron is in your body but locked away in storage, unable to get where it’s needed. This has a name: anemia of inflammation, sometimes called anemia of chronic disease. In that case, more iron isn’t the answer, and iron supplements are generally avoided during active infection or inflammation. Calming the source is.

And sometimes the gate isn’t the problem at all. The door to the gut is. Your stomach needs enough acid to get iron into a form your small intestine can absorb. Low stomach acid, or long-term use of acid-blocking medications like PPIs and antacids, can quietly cut how much iron gets in. Celiac disease and inflammatory bowel conditions do the same.

So when someone tells you “you’re just low in iron,” the better question is: low because of what? Not enough coming in? Not getting through the gut? Not getting through the gate? Locked in storage? Each answer leads somewhere different.

Clue #2 — When the Gate Won’t Close

Genes can push iron the other way too. Variations in the HFE gene are behind hereditary hemochromatosis, where the body absorbs too much iron and stores it in the liver, heart, pancreas and joints. According to the Canadian Hemochromatosis Society, it’s the most common genetic disorder in Canada, with an estimated 80,000 Canadians carrying two copies of the gene.

This matters more as life changes. Monthly cycles act as a natural release valve for iron. Once they stop, iron can start building up quietly. The early signs, like fatigue, achy joints and brain fog, are easy to write off as stress, a demanding job, or “just getting older.”

Notice something? Those are the same complaints that send people looking for an iron supplement. Taking iron “just in case” is the last thing this body needs. That’s why testing comes before supplementing, every time.

Clue #3 — Anemia, Memory and the Brain

“Anemia” gets used as if it means “low iron.” It doesn’t. Anemia simply means you have fewer red blood cells, or less hemoglobin, than you need to carry oxygen around your body. It’s a sign that something is off, not the full diagnosis.

Iron deficiency is the most common cause. But two other nutrients matter just as much: vitamin B12 and folate. Your body needs both to build healthy red blood cells. Without them, it makes fewer cells that are oversized and poorly formed. That’s why a basic blood count is so useful. Small, pale red blood cells point toward iron. Large ones point toward B12 or folate.

This is where the brain enters the case.

Your brain is one of the hungriest organs you have, and it depends on a steady oxygen supply. In an 11-year study of more than 2,500 older adults, those with anemia at the start had a higher risk of developing dementia, even after accounting for other health conditions and the APOE4 gene. The researchers were careful to say this shows a link, not proof that anemia causes dementia. Anemia may also be a marker of other things going on in the body. Still, it’s a clue worth taking seriously.

Vitamin B12 is the stronger thread. B12 is needed to build myelin, the protective coating around your nerves, and to keep a compound called homocysteine in check. When B12 runs low for a long time, the damage can go beyond tiredness: numbness and tingling, balance problems, mood changes and memory loss that can look a lot like early dementia. A review on vitamin B12 and cognitive impairment found that low B12 is associated with cognitive decline. The catch: nerve damage from a long-standing deficiency isn’t always fully reversible, which is why catching it early matters so much.

Your body stores B12 in the liver for years, so a deficiency builds slowly and quietly. It often runs low because of pernicious anemia, an autoimmune condition that blocks B12 absorption. Low stomach acid and long-term medications like metformin and acid blockers can do the same. So can a plant-based diet without a reliable B12 source, and gut conditions like celiac disease or Crohn’s.

And yes, genetics plays a part here too. A genome-wide study in Nature Genetics found that common variants in a gene called FUT2 are linked to differences in blood B12 levels. Genes in the methylation pathway, like MTHFR, also affect how well your body puts folate to work. Two people eating the same diet can end up with very different B12 and folate status.

Too Much Iron and the Brain

Iron balance matters for the brain in both directions. Research using specialized MRI scans has found that higher iron in certain brain regions was linked with faster cognitive decline in people who already showed the early protein changes of Alzheimer’s disease. This is still an emerging area, and it isn’t about the iron on your plate. But it’s one more reason the answer to “low energy, foggy brain” is never simply “take more iron.”

Smart Pairings

Plant iron + vitamin C: Lentils with peppers, spinach with a squeeze of lemon, oatmeal with strawberries. Vitamin C helps convert plant (non-heme) iron into a form your gut absorbs more easily.

Plant iron + a little meat or fish: Adding even a small amount of meat, poultry or fish to a bean or grain dish improves how much plant iron you absorb.

Cook in cast iron: Simmering acidic foods like tomato sauce in a cast iron pan adds a little extra iron to the meal.

Keep apart: Tea, coffee and calcium-rich foods or supplements can block iron absorption. Leave about two hours between your iron-rich meal (or iron supplement) and your coffee, tea or calcium.

Nutritional Support

Food comes first. Supplements are best chosen with a practitioner who has seen your blood work, because the right choice for one genetic profile can be the wrong one for another.

Iron Support (After Testing, Never “Just in Case”)

Food first: Heme iron from beef, lamb, sardines, mussels and dark-meat poultry is absorbed more easily and is less affected by what else is on your plate. Plant sources include lentils, chickpeas, pumpkin seeds, tofu and blackstrap molasses, paired with vitamin C.

Supplement forms: Iron bisglycinate is gentler on the stomach and well absorbed. Heme iron polypeptide is an option for people who don’t tolerate other forms. Alternate-day dosing may improve absorption, especially if hepcidin runs high.

Supporting nutrients: Vitamin C improves plant iron absorption. Vitamin A helps release iron from storage (more on vitamin A in Part 2). Copper is needed to move iron into circulation. Low vitamin D has also been linked with lower iron status. Take iron away from zinc, calcium and vitamin E supplements, which compete with it.

If inflammation is the story: Focus on omega-3 rich foods, colourful vegetables and fibre to calm the source, rather than adding more iron to a locked system.

B12 and Folate Support (Test B12 First)

Food first: B12 is found only in animal foods: clams, mussels, sardines, salmon, beef, eggs and dairy. Folate comes from leafy greens, asparagus, lentils, chickpeas and avocado. Folate is fragile, so lightly steamed or raw greens hold more of it than long-cooked ones.

Supplement forms: Methylcobalamin and adenosylcobalamin are the active forms of B12 your body uses directly, a step ahead of cyanocobalamin. Sublingual B12 can help when absorption is a concern, but pernicious anemia often needs B12 injections through your doctor. For folate, methylfolate (5-MTHF) or folinic acid are better choices than synthetic folic acid, especially with MTHFR variants.

Supporting nutrients: Vitamin B6 works alongside B12 and folate to keep homocysteine in check, which matters for both your heart and your brain.

Gut Support

Every nutrient in this article depends on your gut to get in. Steady fibre from vegetables, legumes and oats keeps elimination regular, and healthy stomach acid matters for both iron and B12. If you’ve been on acid blockers for years, ask your doctor whether you still need them, and don’t stop them on your own.

Red Flags: When to Investigate Further

Talk to your doctor and ask for testing if you notice:

Iron concerns: Ongoing fatigue, breathlessness on stairs, restless legs, hair shedding, brittle or spoon-shaped nails, or cold hands that don’t improve with iron. Ask for a CBC and a full iron panel: ferritin, serum iron, total iron-binding capacity (TIBC), transferrin saturation, plus CRP to check for inflammation. A ferritin result alone can be misleading.

Possible iron overload: Unexplained fatigue, joint pain (especially in the knuckles of the index and middle fingers), abdominal discomfort, darkening skin, or a family history of hemochromatosis. A transferrin saturation and ferritin test is the first step, and HFE genetic testing through your doctor confirms the diagnosis. Don’t take iron supplements until this is ruled out.

B12 or folate concerns: Numbness or tingling in your hands or feet, balance problems, memory or mood changes, a sore red tongue or cracks at the corners of your mouth. Ask for a CBC with MCV (red blood cell size), serum B12 and folate, and if B12 is borderline, methylmalonic acid (MMA) and homocysteine. If pernicious anemia is suspected, intrinsic factor antibodies help confirm it. If you take metformin or an acid blocker long term, ask about checking B12 regularly.

Memory changes: New forgetfulness, trouble concentrating or word-finding difficulties always deserve a proper medical assessment. Blood work for anemia, B12, folate and thyroid is part of ruling out treatable causes, not a replacement for that assessment.

Closing the Case

Low iron on a good diet doesn’t mean you’ve been doing it wrong. It may mean your gatekeeper runs strict, your iron is locked in storage, or the real culprit is B12 or folate. Or, for some, it means iron is the last thing the body needs.

That’s why the question is never just “how low?” It’s “low because of what?” Your genes hold part of the answer. Your blood work holds the rest.

In Part 2, we follow the same trail into two nutrients your body has to convert before it can use them: vitamin A and omega-3. That’s where all the carrots in the world, and a spoonful of seeds, come in.

Next in the series: Part 2 — Carrots, Flax and Your Genes: The Conversion Clues →