Why iron needs vary so widely
Iron is one of the few nutrients where the recommended intake varies by a factor of three-plus across normal adult demographics. A 25-year-old menstruating woman needs more than twice as much iron as her 30-year-old male partner. A pregnant woman needs roughly three times as much. Post-menopause, women’s needs drop back to the male baseline.
Heme vs non-heme iron
Animal foods (meat, poultry, fish) contain heme iron, which the body absorbs efficiently (15–35%). Plant foods (lentils, spinach, fortified cereals) contain non-heme iron, which the body absorbs much less efficiently (5–12%). Vitamin C eaten in the same meal can roughly double non-heme iron absorption; tea and coffee in the same meal can cut it nearly in half.
For vegetarians and vegans, the IOM’s standard adjustment is to multiply the RDA by 1.8. So an 18 mg female RDA becomes ~32 mg/day in a vegan diet, and an 8 mg male RDA becomes ~14 mg/day.
Why this isn’t a supplement recommendation
Iron deficiency anaemia is real, common, and worth investigating. But starting an over-the-counter iron supplement based on tiredness, web searches, or a calculator result is genuinely risky. Iron overload (hemochromatosis) is one of the most common inherited conditions in Canadians of Northern European descent, affecting roughly 1 in 250. People who have it absorb iron more aggressively than average and accumulate it in the liver, heart and pancreas over decades — and unnecessary supplementation can accelerate the damage.
The right path is: a routine ferritin + transferrin saturation + haemoglobin blood panel through your doctor. If you’re iron-deficient by lab values, your physician will recommend a specific dose and re-test you. If you’re not, you don’t need a supplement.