Mineral
Iron
Iron requires 18 mg daily for adult women and 8 mg for men. The tolerable upper intake level is 45 mg. It has 2 severe interactions, notably with Calcium citrate and Iron bisglycinate.
What Iron does
Carries oxygen in haemoglobin and supports mitochondrial electron transport.
Heme iron absorbs far better than non-heme. RDA is 27 mg during pregnancy.
How much you need
| Measure | Adult male | Adult female |
|---|---|---|
| Recommended intake | 8 mg | 18 mg |
| Upper intake level | 45 mg | |
| Typical supplement dose | 18-27 mg elemental · 100 g | |
Interactions involving Iron
14 sourced rules| Pair | Severity | Mechanism | Action |
|---|---|---|---|
| Calcium citrate × Iron bisglycinateseparate 2h | Severe | Calcium and non-heme iron compete for the same divalent metal transporter (DMT1) in the small intestine. Calcium also inhibits iron absorption directly, and the effect is proportional to dose. | Separate calcium and iron by at least 2 hours. Take iron on an empty stomach with vitamin C, and calcium with a meal later in the day.Source |
| Iron bisglycinate × Levothyroxineseparate 4h | Severe | Iron forms insoluble chelates with levothyroxine in the gut, sharply reducing how much thyroid hormone is absorbed and destabilising TSH. | Take levothyroxine first thing on an empty stomach, then wait at least 4 hours before iron.Source |
| Zinc picolinate × Iron bisglycinateseparate 2h | Moderate | Zinc and iron are both absorbed through DMT1 and compete directly, which is why each can blunt the other when taken together. | Separate zinc and iron by at least 2 hours. If you need both at high doses, take iron in the morning and zinc in the evening.Source |
| Iron bisglycinate × Coffeeseparate 1h | Moderate | Polyphenols in coffee, chiefly chlorogenic acid, bind non-heme iron in the gut and can reduce its absorption by 40-60% when consumed within an hour. | Wait at least one hour after iron before coffee — ideally longer. Take iron with vitamin C instead.Source |
| Iron bisglycinate × Black teaseparate 1h | Moderate | Tannins in black tea form insoluble complexes with non-heme iron, cutting absorption by up to 60-70% at the same meal. | Leave at least 1 hour between iron and tea. Drink tea between meals rather than with them.Source |
| Iron bisglycinate × Dairy (milk, yoghurt)separate 2h | Moderate | The calcium in dairy blocks non-heme iron absorption at the same meal, and casein and whey proteins may also inhibit it. | Take iron away from dairy; use a calcium-free meal or an empty stomach as the iron window.Source |
| Zinc picolinate × Fortified cerealseparate 2h | Moderate | Phytates in grains and fortified cereals chelate zinc and inhibit its absorption dose-dependently. | Take zinc between meals, or choose a chelated form such as zinc picolinate which resists phytate binding.Source |
| Iron bisglycinate × Proton pump inhibitor | Moderate | Iron needs gastric acid to convert to its absorbable ferrous form; proton pump inhibitors reduce that conversion substantially. | Take iron with vitamin C to compensate, or discuss with your prescriber if ferritin is not responding.Source |
| Green tea extract (EGCG) × Iron bisglycinateseparate 1h | Moderate | Polyphenols in green tea, including EGCG, chelate iron and inhibit its absorption. | Separate green tea extract from iron by at least 1 hour, or take iron with vitamin C instead.Source |
| Iron bisglycinate × Fluoroquinolone antibioticseparate 3h | Moderate | Iron forms insoluble complexes with fluoroquinolones, lowering antibiotic absorption. | Take the antibiotic 2 hours before or 6 hours after iron.Source |
| Iron bisglycinate × Manganeseseparate 2h | Mild | Iron and manganese share the DMT1 transporter and can mutually reduce absorption. | Keep manganese in a multivitamin rather than a standalone high dose, and take it at a different meal from iron.Source |
| Iron bisglycinate × Red meat | Synergy | Heme iron from meat is absorbed by a separate pathway and also enhances absorption of non-heme iron from plants eaten at the same meal. | Take plant iron sources with a small serving of meat, poultry or fish to lift absorption.Source |
| Iron bisglycinate × Vitamin C | Synergy | Ascorbic acid reduces ferric iron to the ferrous form and chelates it, which can multiply non-heme iron absorption several-fold. | Take 100-500 mg vitamin C with your iron dose. This is the single most effective pairing for iron.Source |
| Iron bisglycinate × Red meat | Synergy | Heme iron from meat is absorbed intact and also enhances uptake of non-heme iron eaten at the same meal. | Combine plant iron sources with a small serving of meat, poultry or fish.Source |