Iron: the deficiency that hides as bad training

Up to 60 percent of female athletes, depending on discipline, training load and menstrual status. The most prevalent nutritional deficiency in female sport, and the one that is hardest to see because it looks like everything else.

Flat in training. Tired in a way sleep does not fix. Sessions that used to feel routine feel heavy.

Every one of those points at half a dozen things, and iron is the one nobody checks.

Why it compounds instead of just adding

What makes iron different from a straightforward shortfall.

Iron deficiency anaemia reduces appetite. A fighter who is already eating less than she needs now wants food less, which deepens the energy deficit that may have caused the problem.

It also affects thyroid function and metabolic efficiency, both of which sit downstream of energy availability too.

What supplementation does, when it is indicated

A systematic review published in 2025 in the Journal of Sport and Health Science examined iron deficiency, supplementation and performance in female athletes.

High-level female athletes with iron deficiency showed impaired endurance performance. That impairment improved with supplementation of approximately 100 mg of elemental iron per day, or on alternate days.

Alternate-day dosing appears in the recent literature because of how iron absorption is regulated. A dose raises hepcidin, the hormone that controls iron uptake, which blunts absorption of the doses that follow. Leaving a day between them works around that.

This is a live area and worth discussing with whoever prescribes it rather than deciding alone.

The part where I stop giving advice

Everything else on this site you can act on yourself. Not this.

Iron requires a blood test, including ferritin. Three reasons, and each is sufficient on its own.

• Excess iron is harmful. Unlike a vitamin where extra is simply wasted, iron accumulates.
• The symptoms are non-specific. Fatigue, poor training, low mood and breathlessness all look identical whether the cause is iron, energy availability, sleep, thyroid, or simply a hard block.
• You cannot know without measuring. There is no way to feel the difference between low ferritin and a fatiguing camp.

So: test before supplementing, and test again afterwards to see whether it worked. A physician orders it, reads it in context, and decides the dose.

That is the whole recommendation and I would not soften it.

What you can do without a prescription

Food, and it is not trivial. The absorption differences are large enough to matter.

Vitamin C in the same meal improves non-haem absorption. Peppers, citrus, tomatoes alongside the beans or the greens.

Tea and coffee with a meal reduce it. Polyphenols bind iron. Moving your coffee an hour either side of the meal costs nothing and it is one of the easiest wins available.

That last point matters more in this sport than most, because fighters drink a lot of coffee and often with food.

Why fighters specifically

Three things stack in this sport, and none of them is mysterious.

Restriction. A camp is an extended period of reduced intake, and red meat is often among the first things reduced because of its energy density.

That removes the best-absorbed form of iron at exactly the point demand is highest.

Menstrual losses. Ongoing, and larger in some women than others.

Training load. High-volume training raises iron demand through pathways that deliver oxygen to working muscle.

None of that is unique to combat sports, but the combination of an 8-week deficit with a hard training load and monthly losses is a fairly specific pressure.

What I would put in a plan

Test at the start of camp, not when something goes wrong. A baseline ferritin taken when you feel fine is worth far more than one taken in week six, because then you have two numbers instead of one.

Protect haem iron sources through the camp. If red meat is being cut for energy reasons, leaner cuts keep the iron and lose the fat. That is a better trade than removing it.

Separate coffee from meals. Free, and it works.

Never supplement on a hunch. Including the low-dose supermarket product, which is still iron.

If a doctor prescribes it, take it as prescribed and retest. Iron is slow. Weeks, not days, and stopping when you start feeling better is how people end up back where they started.

The sentence I would want a coach to hear

When a female athlete's training quality drops and stays down, the assumption in most gyms is that she needs to work harder or that she is not committed. The same assumption gets made about male fighters, where the prevalence is lower but a restricted phase removes the thing protecting them.

Up to 60 percent prevalence makes the alternative explanation an ordinary one, and checking it takes a blood test that costs less than a week of a camp spent going backwards.