Iron: what to pair and what to space apart

Iron pairs synergistically with Vitamin C, the simplest and best-evidenced absorption enhancer. Lactoferrin and a small amount of meat protein (the 'meat factor') also enhance non-heme iron absorption. Iron antagonises calcium, zinc, copper, magnesium, and manganese at the same dose, space mineral supplements by at least 2 hours. Iron also reduces absorption of levothyroxine, levodopa, methyldopa, bisphosphonates, fluoroquinolone and tetracycline antibiotics, mycophenolate, and penicillamine, space these by 2 to 4 hours. Coffee, black tea, green tea, red wine, cocoa, and high-fibre cereal all reduce iron absorption when consumed at the same meal. PPIs and H2 blockers reduce iron absorption modestly over months; people on long-term acid suppression should monitor ferritin.

The most common iron mistakes are taking it with coffee, tea, or breakfast cereal (which blocks most of the dose), taking it daily when alternate-day dosing absorbs more, choosing high-dose ferrous sulfate when ferrous bisglycinate is far gentler, and self-supplementing without measuring ferritin. Another frequent error is stopping at the first sign of normal haemoglobin without rebuilding ferritin stores, which takes 3 to 6 months. Constipation is common; bisglycinate, alternate-day dosing, and a magnesium citrate buffer in the evening usually resolve it. Finally, taking iron with calcium-rich antacids or a calcium supplement at the same time can block more than half the iron dose.

When something has to be spaced apart, two slots are almost always enough. Put one group with your first meal and the other with your evening meal, roughly 8 to 12 hours apart, which comfortably clears the 2-hour intervals absorption conflicts require. Iron goes in the earlier slot, and anything it competes with goes in the other. Trying to run three or four slots is where routines break down, most people can hold two.

Absorption conflicts are dose-dependent, not absolute. Trace amounts in food, a splash of milk in coffee or the calcium in a slice of bread, are not the same as a 500mg supplement, and are not worth restructuring your day around. The interactions worth respecting are between two supplements at supplemental doses taken in the same swallow. If you are only taking Iron and nothing else, spacing is a non-issue, keep it in a fixed slot and move on.

• Iron and Calcium
• Iron and Zinc
• Iron and Vitamin C
• Iron and Magnesium Glycinate

• Calcium (blocks up to 60%)
• Coffee/tea (tannins)
• Zinc
• Dairy
• Whole grains

• Do I need to take iron with Vitamin C?+

  It significantly helps. Vitamin C reduces ferric iron to the more absorbable ferrous form and can boost non-heme iron absorption by up to 67 percent. A glass of orange juice, a kiwi, or 250 mg of ascorbic acid alongside the iron dose is the simplest version. Heme iron from animal sources does not need this boost.
• Can I take Iron in the same handful as everything else?+

  Not quite. Iron has documented conflicts with Calcium (blocks up to 60%) and Coffee/tea (tannins), which is what the spacing table above is for. Everything else can go in the same slot.
• Is spacing measured from swallowing or from digestion?+

  From swallowing. The intervals in the table are conventional practical margins that allow the first dose to clear the absorption window in the upper small intestine before the second arrives. There is no need to be precise to the minute, being roughly two hours apart is the point.

• Hallberg L, et al. Am J Clin Nutr. 1991
• Stoffel NU, et al. Lancet Haematol. 2020