The Healthspan Map · Nutrient

Iron

Linked to getting too little

Where a shortfall of Iron is linked — 16 sources.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Nutrient or lever	Direction	Strength	Evidence type	What was found	Source
Iron	Eat enough of	Strong	Established clinical	Iron deficiency is the leading cause of anemia worldwide.	WHO — Anaemia fact sheet (opens in a new tab)
Iron	Eat enough of	Strong	Established clinical	Iron deficiency is the leading cause of anemia worldwide.	NIH Office of Dietary Supplements — Iron (opens in a new tab)
Iron	Eat enough of	Emerging	RCT / trial	Genetically lower iron status raises anxiety-disorder risk; iron-deficiency anemia relates to more anxiety.	Iron-status MR 2024; Trace-minerals & anxiety review 2023 (opens in a new tab)
Iron	Eat enough of	Emerging	Cohort / observational	Genetically lower iron status raises anxiety-disorder risk; iron-deficiency anemia relates to more anxiety.	"The causal effect of iron status on risk of anxiety disorders: a two-sample Mendelian randomization study", PLoS One 2024 (opens in a new tab)
Iron	Eat enough of	Moderate	Established clinical	Deficiency causes difficulty concentrating and poor memory; in infants/children it can cause lasting cognitive and developmental impairment.	NIH ODS / NHLBI – Iron (opens in a new tab)
Iron	Eat enough of	Moderate	Established clinical	Deficiency causes difficulty concentrating and poor memory; in infants/children it can cause lasting cognitive and developmental impairment.	NIH Office of Dietary Supplements — Iron (opens in a new tab)
Iron	Eat enough of	Strong	RCT / meta-analysis	Iron deficiency even without anaemia is a well-supported cause of fatigue (clearest in low-ferritin menstruating women and athletes); repletion improves it.	Iron-deficiency-without-anaemia & fatigue meta-analysis (Br J Nutr) (opens in a new tab)
Iron	Eat enough of	Moderate	Cohort / observational	Iron deficiency is linked to low mood, anxiety and anhedonia and is sometimes misdiagnosed as depression; symptoms improve with repletion.	Psychiatric-IDA review (PMC10595923) (opens in a new tab)
Iron	Eat enough of	Moderate	Systematic review	Iron deficiency causes restless legs syndrome and fragmented sleep; low iron is linked to short sleep and disrupted dopaminergic sleep-wake control.	Micronutrient-sleep review (opens in a new tab)
Iron	Eat enough of	Moderate	Review / narrative	Iron carries oxygen in haemoglobin and myoglobin; deficiency reduces muscle energy production, causing fatigue and weakness.	Iron & muscle function (opens in a new tab)
Iron	Eat enough of	Moderate	Cohort / observational	Higher iron intake from plants and supplements was part of the "fertility diet" linked to markedly lower ovulatory-disorder infertility.	Diet & ovulatory-disorder infertility (Chavarro, NHS-II) (opens in a new tab)
Iron	Eat enough of	Moderate	Review / narrative	Iron deficiency impairs respiratory burst, bacterial killing, NK activity and T-cell responses needed for airway defence.	Nutritional supplements & viral respiratory infections (ScienceDirect 2024) (opens in a new tab)
Iron	Eat enough of	Moderate	Review / narrative	Iron deficiency (low ferritin) is the most common nutritional cause of hair loss, plus brittle nails and dry skin.	Iron/ferritin & hair loss (opens in a new tab)
Iron	Eat enough of	Moderate	Review / narrative	Thyroid peroxidase is heme-dependent; iron deficiency is strongly associated with hypothyroid status and impairs hormone synthesis.	Minerals & autoimmune hypothyroidism review (PMC7574993) (opens in a new tab)
Iron	Eat enough of	Emerging	Cohort / observational	Lower iron intake was associated with higher tinnitus incidence, though the direction of iron effects is mixed.	Iron & tinnitus incidence (opens in a new tab)
Iron	Eat enough of	Moderate	Review / narrative	Iron is required for lymphocyte proliferation and macrophage pathogen-killing; deficiency impairs immunity.	Iron & immune cells (opens in a new tab)

Linked to getting too much

Where an excess of Iron is linked — 9 sources.In the order the Map holds them: strongest evidence first. That is a statement about the evidence, not about what matters most.
Nutrient or lever	Direction	Strength	Evidence type	What was found	Source
Iron	Don't overdo	Moderate	Established clinical	Iron overload (hemochromatosis) commonly presents with fatigue — the both-sides flip of the iron story.	Iron overload / hemochromatosis symptoms (opens in a new tab)
Iron	Don't overdo	Moderate	Established clinical	Iron overload (hemochromatosis) commonly presents with fatigue — the both-sides flip of the iron story.	NIH Office of Dietary Supplements — Iron (opens in a new tab)
Iron	Don't overdo	Moderate	RCT / trial	Oral iron commonly causes nausea (~22%), constipation (~24%) and heartburn.	Oral iron GI side effects (opens in a new tab)
Iron	Don't overdo	Emerging	Review / narrative	Excess iron generates oxidative stress in seminal plasma that can damage sperm; iron overload is unfavourable to reproductive cells.	Diet & male infertility (PMC7291266) (opens in a new tab)
Iron	Don't overdo	Moderate	Review / narrative	Iron overload/indiscriminate supplementation increases susceptibility to infection, since pathogens exploit available iron ("nutritional immunity").	Nutritional supplements & viral respiratory infections (ScienceDirect 2024) (opens in a new tab)
Iron	Don't overdo	Emerging	Review / narrative	Excess iron promotes bacterial growth and oxidative stress ("nutritional immunity"), a risk when over-supplemented.	Iron overload & infection (opens in a new tab)
Iron	Don't overdo	Strong	Established clinical	Chronic iron overload (hemochromatosis or excess intake) deposits in the liver, progressing from fibrosis to cirrhosis and cancer.	Iron overload & toxicity (StatPearls NBK526131) (opens in a new tab)
Iron	Don't overdo	Moderate	Established clinical	Iron deposition in the heart causes cardiomyopathy and arrhythmias.	NIH ODS – Iron (hemochromatosis) (opens in a new tab)
Iron	Don't overdo	Emerging	Mechanistic	High-dose iron competitively decreases zinc absorption.	NIH ODS – Iron (opens in a new tab)