Is it better not to take iron and calcium together?

Calcium does inhibit the absorption of non-haem iron in the gut, and this has been demonstrated in multiple human studies. Non-haem iron is found in plant-based foods and most supplements. This is a real short-term effect: when you take calcium and non-haem iron at the same time, the gut absorbs less iron than when you take them separately.

In practice, however, this matters little for healthy people. Long-term research shows that people who consistently take higher amounts of calcium still maintain normal iron levels in the blood. Blood markers such as haemoglobin and ferritin do not deteriorate. The gut appears to compensate over time. Strictly separating calcium and iron is therefore probably not necessary for healthy people.

Haem iron, from meat, fish and poultry, is largely unaffected by calcium. It is well absorbed regardless and is barely inhibited by most nutrients. Vitamin C does the opposite: it strongly improves the absorption of non-haem iron and can even cancel out the inhibiting effect of calcium. A glass of orange juice with an iron-rich plant-based meal is therefore more useful than worrying about when to take your calcium supplement.

There are two situations in which the combination is clinically relevant. Do you use thyroid medication (levothyroxine)? Both calcium and iron bind the medication in the gut, meaning you absorb noticeably less of it. Take those supplements at least four hours apart. The same applies to certain antibiotics, such as ciprofloxacin: iron and calcium supplements reduce the absorption of this antibiotic. Discuss the timing with your pharmacist or doctor if you use this type of medication.