Why does the iron figure differ for men and women?

Iron requirements are not the same for everyone. They differ clearly by sex and life stage, and that is the part people most often do not know.

How different are the recommended intakes?

The recommended intakes set by the US National Academies' Food and Nutrition Board, as published by the NIH Office of Dietary Supplements, are 8 mg a day for adult men and 18 mg a day for women aged 19 to 50, roughly double.

From age 51, the figure for women is 8 mg, the same as for men. During pregnancy it rises to 27 mg a day.

Why the difference?

The main reason is the blood lost over the monthly cycle, which carries iron with it in an amount the body then has to replace. This is normal physiology, not a problem, and it is why the reference figures were set differently in the first place.

Once menstruation ends, that loss stops and the recommended intake drops. The reference values are set by age band rather than as one figure for a whole lifetime.

Is food alone enough?

For many people, a varied diet that includes both animal and plant sources is sufficient, particularly when vitamin C is in the same meal as plant-source iron.

For people eating vegetarian or vegan diets, all dietary iron is non-haem and absorbed less efficiently. Oxalate in spinach and phytate in beans and grains limit it further, and soaking or fermenting reduces phytate.

Is there an upper limit?

Yes. The tolerable upper intake level for adults is 45 mg a day from all sources combined. Iron is a mineral the body has no easy route for clearing, so a high-dose supplement is something to discuss with a doctor or pharmacist first.

What can you do day to day?

Keep an iron source in meals regularly, put a vitamin C-rich vegetable or fruit in the same meal as plant-source iron, and move tea and coffee to between meals.

Dietary supplements are not intended to prevent, treat or cure any disease.