Iron Supplementation Forms: What the Absorption Research Reports (Ferrous Sulfate, Fumarate, Bisglycinate)

Iron deficiency is the most prevalent micronutrient deficiency both globally and in the UK. The National Diet and Nutrition Survey (NDNS) — the UK's rolling survey of dietary intake and nutritional biomarkers — provides the most detailed population-level data. Key findings from the NDNS consistently show that substantial proportions of the UK population have low iron intakes relative to the Reference Nutrient Intake (RNI), with certain subgroups at substantially elevated risk. Among UK women of reproductive age (16–49), NDNS data show that approximately 48% have dietary iron intakes below the RNI of 14.8 mg/day, and approximately 25% have low serum ferritin (below 15 µg/L, indicating depleted stores). Iron-deficiency anaemia — defined by low haemoglobin in conjunction with low ferritin — affects an estimated 14–18% of UK pre-menopausal women, with higher rates in those with heavy menstrual loss (clinically significant menorrhagia). Vegetarians and vegans are at elevated risk because plant-based foods contain only non-haem iron — the less bioavailable iron form. Haem iron (from meat) is absorbed at rates of 15–35%, while non-haem iron from plant foods is absorbed at only 2–20%, depending strongly on dietary co-factors. A systematic review of iron status in vegetarian populations found mean serum ferritin approximately 30% lower in vegetarians compared to omnivores, with depleted stores (ferritin below 15 µg/L) documented in 40–50% of female vegetarians across multiple European cohorts (PMID: 21412952). Endurance athletes represent another at-risk group. Mechanisms include foot-strike haemolysis (in long-distance runners), increased iron losses via sweat and the gastrointestinal tract, and elevated iron demand from increased erythropoiesis and myoglobin turnover. A meta-analysis published in the British Journal of Nutrition (2019) found iron deficiency without anaemia in approximately 35% of female endurance athletes studied across 11 studies (PMID: 30688192). The NHS guidance on iron is unambiguous: 'do not take iron supplements unless your GP has said you have iron deficiency or iron deficiency anaemia'. This caution reflects the unique characteristic of iron metabolism — the body lacks active excretion mechanisms, so surplus iron accumulates and can cause oxidative tissue damage. Haemochromatosis (the HFE gene variant causing iron overabsorption) affects approximately 1 in 200 UK individuals of Northern European ancestry and can lead to organ damage if iron loading continues unchecked. BS (British Society of Haematology) and BSG (British Society of Gastroenterology) guidance recommends investigating the underlying cause of iron deficiency — particularly in post-menopausal women and adult men, where gastrointestinal malignancy must be excluded — before initiating supplementation (PMID: 21561874).