Iron, periods and why deficiency is more common in women

Iron deficiency is the most common nutritional deficiency in Australia, and it is not evenly distributed: menstruating women carry several times the risk of men — for reasons that are entirely mechanical.

The arithmetic of iron loss

The body has no way to excrete excess iron, so it runs a tight budget: small daily losses, matched by absorption from food. Menstruation adds a regular withdrawal to that budget — blood is where the body's iron lives, so blood loss is iron loss, every cycle, for decades.

For many women the budget still balances. But the margin is thin, and three things routinely tip it: heavier periods, which multiply the withdrawal; pregnancy and breastfeeding, which are enormous iron investments; and lower dietary intake — iron from plant sources is absorbed less readily, so vegetarian and vegan diets need deliberate attention to the balance.

Why it goes unnoticed

Iron deficiency arrives gradually, and its early symptoms — tiredness, reduced exercise tolerance, poor concentration — are easy to attribute to life. Many women normalise both the fatigue and the heavy periods driving it, because both have always been there. This is a deficiency people carry for years, functioning below par without a name for it.

What testing shows, in sequence

Ferritin — the storage marker — falls first, often long before anything else changes. This is the stage worth catching: stores low, function still holding, fix straightforward. Left to run, serum iron falls, transferrin rises to compensate, and eventually haemoglobin drops — iron deficiency anaemia, the late chapter of a long story. A full iron studies panel reads the stage, not just the headline, and a normal full blood count does not rule out depleted stores.

Two things that matter beyond the test

Heavy bleeding is itself worth raising. If periods are heavy enough to drive deficiency, the bleeding deserves its own assessment — causes range from the entirely benign to the treatable, and a GP can sort them. Treating the iron without asking about the tap leaves the tap running.

Don't self-supplement blind. Iron supplements are not harmless — they commonly cause gut side effects, they can mask the pattern a doctor needs to see, and in people with undiagnosed iron-overload conditions they do genuine harm. Test first, supplement on advice, retest to confirm stores rebuilt — which takes months, not weeks.

What this won't tell you

• Fatigue has many causes. Iron is a common one in menstruating women, not the default explanation — testing distinguishes rather than assumes.
• Ferritin has a blind spot. It rises with inflammation, so recent illness can mask low stores; context and sometimes repeat testing resolve it.
• The fix isn't always dietary. Where losses outpace absorption, food alone may not close the gap — that judgement is a doctor's.

The bottom line

Menstruation makes iron a budget under standing pressure, and ferritin is the early-warning gauge. For any menstruating woman with unexplained flatness — and for anyone with heavy periods regardless — iron studies are among the highest-yield tests on the menu, and the earlier the stage, the easier the fix.