Fatigue is the symptom most likely to be waved away, by doctors and by the women carrying it. It is also one of the most informative, because the things that cause it in women are specific, measurable, and frequently missed.
Why fatigue in women rarely has a single cause
Unlike the fatigue of one bad night or one heavy week, fatigue that settles in over months usually combines several factors that feed each other: degraded sleep worsens stress, stress disturbs the cycle, a disturbed cycle affects sleep. It is that loop, rather than any single link in it, that makes chronic fatigue so resistant to one isolated fix.
The most common causes in women
Low iron, even without frank anaemia, is one of the best-documented causes of fatigue in women of reproductive age, tied to menstrual losses — and one of the few where a randomised trial has shown supplementation helps. An underactive thyroid is another classic, often alongside feeling cold and weight gain. Chronic stress sustains a fatigue that rest alone does not resolve. And hormonal shifts — the premenstrual phase, perimenopause — have a direct and documented effect on how much energy you have.
Where to start
Rather than hunting for one cause, it is more useful to look at the whole: real sleep, both duration and quality; stress load; diet; and where you are in your cycle. Measuring some biology — ferritin above all, alongside a full blood count and TSH — can confirm or rule out a lead, provided it is read within the whole picture rather than as an isolated number.
- Look at your actual sleep first — duration and quality — it is the most commonly skipped lever.
- Note whether the fatigue moves with your cycle. A clear pattern narrows things down considerably.
- Do not skip the iron question — it is a frequent and under-diagnosed cause in menstruating women.
- See someone if the fatigue persists for weeks despite enough sleep.
Reviewed by the OVEA medical committee