How Much Iron Adults Need
The NIH Office of Dietary Supplements lists these RDAs [1]:
| Group | RDA |
|---|---|
| Men 19+ | 8 mg |
| Premenopausal women (19–50) | 18 mg |
| Postmenopausal women (51+) | 8 mg |
The large difference reflects iron lost through menstruation. Pregnancy raises needs further.
Who Is Prone to Deficiency
NIH notes higher deficiency risk for pregnant women, infants and young children, women with heavy menstrual bleeding, and frequent blood donors, as well as people with certain cancers, GI disorders, or heart failure [1]. Iron shortfall is the world's most common nutritional deficiency and can cause fatigue and reduced exercise capacity.
Why 'More' Is Risky
Iron is a case where the gap between 'enough' and 'too much' is narrow. The UL is 45 mg/day [1] (see Upper Intake Levels). Risks of excess include:
- GI side effects — constipation, nausea, and stomach pain are common even at supplement doses.
- Iron overload — people with hemochromatosis (a genetic condition) accumulate iron and can be harmed by supplements.
- Accidental poisoning in children — NIH warns that accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6 [1]. Keep iron supplements out of reach.
Don't Supplement Iron 'Just in Case'
Because the body has no easy way to excrete excess iron, you shouldn't take iron supplements without a reason. Fatigue has many causes — confirm low iron with a blood test before supplementing, ideally with a clinician's guidance.