Deep fatigue
Normal, and Exhausted
Your bloods came back fine. You sleep eight hours. You are still tired. There are five or six mechanisms behind that sentence, and one of them was hiding inside a reference range built for someone else.
Tiredness is a touchy subject for me.
For years, for most of my life, I have been tired. Really tired. Even at ten years old, I was tired. You could ask how that is possible for a child, and you would be the first person to ask it, apart from me and my parents.
Every doctor's appointment ended with more question marks than answers. I do not know whether they did not care, or whether it went over their heads, or whether they were simply bored. But no matter how long I slept, no matter what I ate or did or how I moved, I could not shake the feeling. By then it had set in as something heavier than tiredness, and it turned into a real depression on the far side of it.
I am not kidding. I wish I were. I wish I were writing this only for the sake of a blog post. The reality is that every kind of care I was denied as a child, and later as an adult, shaped my life.
But I am not someone who sits and slumbers. So I went out and did something. I started to become my own physician. There is beauty in knowing your own biology as well as I have come to know mine, though that belongs in a different post.
What I want to say here is that I was often ashamed of my fatigue. Every time I had to run in gym class and simply could not. Every morning I biked to school and arrived late, because I could not keep up and got off to walk instead, while swarms of other children cycled past me from the station. I took the bus, or I walked, alone.
And at some point, I do not know exactly when, I started to apologise for it.
Even before I knew what was going on, I knew I was not crazy. I knew there was a logical explanation, and that nobody with the right kind of power wanted to hear it. So I apologised. And then I became rebellious.
This post is the rebellious version. Because fatigue is the symptom people apologise for.
Not pain, which gets taken seriously. Not bleeding, which gets investigated. Tiredness, which arrives at the appointment already half-retracted, because you have heard how it sounds.
Everyone is tired. That is the sentence waiting for you.
Women mention fatigue to a doctor about three times as often as men do.[1] The usual reading of that is that women complain more. The other reading is that something is happening in more women, and it is worth finding out what.
So this post exists to give you the mechanisms. Six of them, each with a different signature, a different blood test, and a different answer. And one of them has a story attached that took twenty-four years to correct.
What kind of tired
Tiredness reads as one thing from outside and as several from inside. The version where you cannot get up a flight of stairs is not the version where you are wired at eleven at night. Those are different mechanisms wearing the same word.
Six kinds below. Most women recognise two.
The Tired Taxonomy
Six kinds of tired that get called the same thing. Tap whichever you recognise.
Why this lands on women
Before the mechanisms, the arithmetic, because it explains why fatigue arrives at a doctor three times more often from women.
You lose iron when you bleed. A period costs you somewhere in the region of a milligram of iron a day averaged across a cycle, and a heavy one costs considerably more. Absorption from food runs at a few milligrams a day at best, and less than that from plants without something acidic alongside. So the margin between what leaves and what arrives is thin, and it stays thin for about forty years.
Add a pregnancy and the account goes further into deficit, because you build another person's blood supply out of your own stores. Add breastfeeding after it. Add a coil that makes your bleeding heavier, or the flooding that arrives in perimenopause, or the long unpredictable bleeds of PMOS.
And the part that keeps this invisible: most women have no idea whether their periods are heavy. You have only ever had your own. The comparison is unavailable, so a bleed that would send a man to a haematologist gets filed under ordinary.
The one that took twenty-four years
Start with iron, because the story of it explains something about all the others.
Your body keeps iron in two places. Some of it is circulating in your red blood cells, and that is what a haemoglobin measurement reads. The rest is stored, and that is what ferritin reads.
You spend the stores first. So there is a stretch, and it can run for years, where your ferritin has emptied out and your haemoglobin has not moved yet. You are iron deficient without being anaemic. Your full blood count comes back clean.
In 2003 a team led by François Verdon at the University of Lausanne ran a double blind placebo controlled trial in 144 women aged 18 to 55, all of them tired, none of them anaemic. Half got oral iron for four weeks, half got placebo. Fatigue dropped 29% in the iron group against 13% on placebo.[2]
And a detail that matters more than the headline. When they broke the results down, only the women with ferritin at or below 50 improved.[2]
Nine years later Paul Vaucher and colleagues, working across 44 primary care practices in France, ran it longer. Twelve weeks, 198 women, same design. Fatigue fell by about 48% on iron against 29% on placebo, and their conclusion named a number: consider iron for women with unexplained fatigue whose ferritin sits below 50.[1]
Their depression and anxiety scores did not shift.[1] So the thing that lifted was tiredness, and only tiredness.
Now hold that number, 50, against what a laboratory calls normal.
Reference ranges vary between laboratories, and they have sat well below 50 for decades. Which produces the situation this whole post is about. A woman whose ferritin would have improved in both of those trials gets a result printed inside the normal range, and a clinician who has no reason to look twice.
Move the slider and watch where you land.
What "Normal" Covers
Ferritin in micrograms per litre. Laboratory ranges differ, so treat the bands as the shape of the problem rather than your local cut-off.
In 2001, three researchers published a question in the BMJ. They asked why women should have lower reference limits for haemoglobin and ferritin than men.[3]
The logic they were querying runs like this. Reference ranges get built from a sample of the population. Take a sample of women, and a large share of them are quietly iron deficient. Average that in, and the bottom of your normal range settles lower than it should. The deficiency becomes the standard, and then the standard makes the deficiency invisible.
That question sat there. The trials arrived in 2003 and 2012 and pointed at the same threshold from a different direction.
And in July 2025, a Canadian team led by Michelle Sholzberg published guidance in CMAJ on iron deficiency in females, noting that the lower limit of normal for ferritin has recently been raised, which will identify more people who would benefit from treatment.[4]
Twenty-four years from the question to the correction. If you were told your bloods were normal at any point in that window, the result may have been accurate and the range may have been wrong.
Tiredness that immune cells make
A second mechanism, and this one explains the specific quality women describe as heaviness.
When your immune system activates, the cytokines it releases do not stay in your tissues. They signal to your brain, and your brain responds with a coordinated set of changes that researchers named sickness behaviour: withdrawal, loss of appetite, more sleep, and fatigue. Robert Dantzer and colleagues mapped this out at the University of Illinois, and the essential point is that the tiredness is manufactured centrally rather than being a shortage of anything.[5]
It is a design feature. When you are fighting something, energy gets pulled away from everything else, and you feel it as exhaustion.
The trouble arrives when the immune activation runs low and long instead of high and brief. The signalling continues at a lower volume, and so does the fatigue, without ever announcing itself as illness. Dantzer's group also traced how prolonged immune signalling to the brain shifts tryptophan metabolism away from serotonin, which is part of why this state and low mood are so hard to separate.[5]
I have written about low-grade inflammation at length elsewhere, so I will point rather than repeat.
The other four
Thyroid. Cold, slow, dry, constipated, gaining weight without a change in what you eat. Thyroid conditions run several times more common in women than men. TSH is the first test and is not the whole picture.
Cortisol and the stress axis. The signature is the mismatch: flattened at three in the afternoon, alert at eleven at night. Wired and tired describes a rhythm that has come out of phase rather than a hormone sitting high or low.
Sleep that looks adequate. Eight hours in bed and you wake wrecked. Sleep-disordered breathing presents differently in women than the textbook picture built on men, showing up as fatigue and low mood rather than obvious daytime sleepiness, and it gets attributed to hormones for years.
The cyclical one. If your tiredness arrives on a schedule, that is information. The luteal phase brings progesterone and its sedative metabolites, then withdraws them. In perimenopause the whole system stops being predictable, and the fatigue that comes with it has a different quality again.
Each of these has its own post on this site, and the taxonomy above links to them.
Normal does not mean no
One habit is worth building, and it is the through line of everything I write here.
A normal test result answers one question. It rarely answers the question you walked in with. Below, the six results most apt to end an investigation early, and what each one leaves open.
What That Result Does Not Rule Out
Six sentences you may have been told, and what each one leaves unanswered. Tap any.
What I would do with all of this
Take the number, not the word. If someone tells you your iron is fine, ask what your ferritin was. The figure is on the report. Both trials pointed at 50 as the level below which tired women improved, and a great many laboratories will print anything above their own lower limit without comment.
Bring a pattern rather than a feeling. Two weeks of notes: what time it hits, whether it tracks your cycle, whether sleep touches it, whether stairs have become a decision. A pattern survives a ten minute appointment. I am tired all the time does not.
Notice which kind you have. The six above want different investigations, and a woman who says I think this is the iron one, and here is why gets a different consultation than a woman who says she is exhausted.
And treat iron with respect rather than enthusiasm. Supplementing without knowing your ferritin is a poor idea, because too much iron carries its own problems and the excess has nowhere to go. Measure first. That is the whole point of this piece.
The thing underneath
Twenty-four years is the part I cannot put down.
The question was asked in 2001, in a major journal, by people who had done the work. The randomised trials followed. And the correction to the reference range arrived in 2025, which means an entire generation of women were handed an accurate result from a range that was set too low, and told there was nothing to find.
None of them were lying about being tired. The instrument was calibrated on a population that was already depleted, and it reported back that the depletion was ordinary.
Which is the same shape as almost everything else I write about here. The measurement was not neutral. Somebody decided what counted as normal, using a sample and a set of assumptions, and then the decision hardened into a number on a printout that nobody thought to question.
You are allowed to question it. Ask what the number was. Ask what the range was built from. Ask what the result rules out and what it leaves standing.
Everyone is tired is not a finding. It is the end of a conversation, and you are allowed to keep it going.
For the women reading
If you have been tired for months and were told your bloods were normal, ask for the ferritin figure. Not whether it was fine. The number. Both randomised trials in non-anaemic tired women found improvement below 50, and laboratory lower limits have historically sat a long way underneath that.
Work out which kind of tired you have before the appointment. Six mechanisms, six different tests, and the one thing that will not help is walking in with the word on its own.
None of this is medical advice, and no article knows your history. Do not start iron without measuring first. Fatigue also has causes this post does not cover, so anything sudden, severe, or accompanied by symptoms that frighten you belongs in front of a doctor rather than a blog.
Sources
- Vaucher, P., Druais, P.-L., Waldvogel, S., & Favrat, B. (2012). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ, 184(11), 1247–1254. https://doi.org/10.1503/cmaj.110950
- Verdon, F., Burnand, B., Fallab Stubi, C.-L., et al. (2003). Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ, 326(7399), 1124. https://doi.org/10.1136/bmj.326.7399.1124
- Rushton, D. H., Dover, R., Sainsbury, A. W., Norris, M. J., Gilkes, J. J. H., & Ramsay, I. D. (2001). Why should women have lower reference limits for haemoglobin and ferritin concentrations than men? BMJ, 322(7298), 1355–1357. https://doi.org/10.1136/bmj.322.7298.1355
- Sholzberg, M., Hillis, C., Crowther, M., & Selby, R. (2025). Diagnosis and management of iron deficiency in females. CMAJ, 197(24), E680–E687. https://doi.org/10.1503/cmaj.240570
- Dantzer, R., O'Connor, J. C., Freund, G. G., Johnson, R. W., & Kelley, K. W. (2008). From inflammation to sickness and depression: when the immune system subjugates the brain. Nature Reviews Neuroscience, 9(1), 46–56. https://doi.org/10.1038/nrn2297
Normal, and Exhausted
Your bloods came back fine. You sleep eight hours. You are still tired. There are five or six mechanisms behind that sentence, and one of them was hiding inside a reference range built for someone else.
Fatigue is the symptom people apologise for.
Not pain, which gets taken seriously. Not bleeding, which gets investigated. Tiredness, which arrives at the appointment already half-retracted, because you have heard how it sounds.
Everyone is tired. That is the sentence waiting for you.
Women mention fatigue to a doctor about three times as often as men do.[1] The usual reading of that is that women complain more. The other reading is that something is happening in more women, and it is worth finding out what.
So this post exists to give you the mechanisms. Six of them, each with a different signature, a different blood test, and a different answer. And one of them has a story attached that took twenty-four years to correct.
What kind of tired
Tiredness reads as one thing from outside and as several from inside. The version where you cannot get up a flight of stairs is not the version where you are wired at eleven at night. Those are different mechanisms wearing the same word.
Six kinds below. Most women recognise two.
The Tired Taxonomy
Six kinds of tired that get called the same thing. Tap whichever you recognise.
Why this lands on women
Before the mechanisms, the arithmetic, because it explains why fatigue arrives at a doctor three times more often from women.
You lose iron when you bleed. A period costs you somewhere in the region of a milligram of iron a day averaged across a cycle, and a heavy one costs considerably more. Absorption from food runs at a few milligrams a day at best, and less than that from plants without something acidic alongside. So the margin between what leaves and what arrives is thin, and it stays thin for about forty years.
Add a pregnancy and the account goes further into deficit, because you build another person's blood supply out of your own stores. Add breastfeeding after it. Add a coil that makes your bleeding heavier, or the flooding that arrives in perimenopause, or the long unpredictable bleeds of PMOS.
And the part that keeps this invisible: most women have no idea whether their periods are heavy. You have only ever had your own. The comparison is unavailable, so a bleed that would send a man to a haematologist gets filed under ordinary.
The one that took twenty-four years
Start with iron, because the story of it explains something about all the others.
Your body keeps iron in two places. Some of it is circulating in your red blood cells, and that is what a haemoglobin measurement reads. The rest is stored, and that is what ferritin reads.
You spend the stores first. So there is a stretch, and it can run for years, where your ferritin has emptied out and your haemoglobin has not moved yet. You are iron deficient without being anaemic. Your full blood count comes back clean.
In 2003 a team led by François Verdon at the University of Lausanne ran a double blind placebo controlled trial in 144 women aged 18 to 55, all of them tired, none of them anaemic. Half got oral iron for four weeks, half got placebo. Fatigue dropped 29% in the iron group against 13% on placebo.[2]
And a detail that matters more than the headline. When they broke the results down, only the women with ferritin at or below 50 improved.[2]
Nine years later Paul Vaucher and colleagues, working across 44 primary care practices in France, ran it longer. Twelve weeks, 198 women, same design. Fatigue fell by about 48% on iron against 29% on placebo, and their conclusion named a number: consider iron for women with unexplained fatigue whose ferritin sits below 50.[1]
Their depression and anxiety scores did not shift.[1] So the thing that lifted was tiredness, and only tiredness.
Now hold that number, 50, against what a laboratory calls normal.
Reference ranges vary between laboratories, and they have sat well below 50 for decades. Which produces the situation this whole post is about. A woman whose ferritin would have improved in both of those trials gets a result printed inside the normal range, and a clinician who has no reason to look twice.
Move the slider and watch where you land.
What "Normal" Covers
Ferritin in micrograms per litre. Laboratory ranges differ, so treat the bands as the shape of the problem rather than your local cut-off.
In 2001, three researchers published a question in the BMJ. They asked why women should have lower reference limits for haemoglobin and ferritin than men.[3]
The logic they were querying runs like this. Reference ranges get built from a sample of the population. Take a sample of women, and a large share of them are quietly iron deficient. Average that in, and the bottom of your normal range settles lower than it should. The deficiency becomes the standard, and then the standard makes the deficiency invisible.
That question sat there. The trials arrived in 2003 and 2012 and pointed at the same threshold from a different direction.
And in July 2025, a Canadian team led by Michelle Sholzberg published guidance in CMAJ on iron deficiency in females, noting that the lower limit of normal for ferritin has recently been raised, which will identify more people who would benefit from treatment.[4]
Twenty-four years from the question to the correction. If you were told your bloods were normal at any point in that window, the result may have been accurate and the range may have been wrong.
Tiredness that immune cells make
A second mechanism, and this one explains the specific quality women describe as heaviness.
When your immune system activates, the cytokines it releases do not stay in your tissues. They signal to your brain, and your brain responds with a coordinated set of changes that researchers named sickness behaviour: withdrawal, loss of appetite, more sleep, and fatigue. Robert Dantzer and colleagues mapped this out at the University of Illinois, and the essential point is that the tiredness is manufactured centrally rather than being a shortage of anything.[5]
It is a design feature. When you are fighting something, energy gets pulled away from everything else, and you feel it as exhaustion.
The trouble arrives when the immune activation runs low and long instead of high and brief. The signalling continues at a lower volume, and so does the fatigue, without ever announcing itself as illness. Dantzer's group also traced how prolonged immune signalling to the brain shifts tryptophan metabolism away from serotonin, which is part of why this state and low mood are so hard to separate.[5]
I have written about low-grade inflammation at length elsewhere, so I will point rather than repeat.
The other four
Thyroid. Cold, slow, dry, constipated, gaining weight without a change in what you eat. Thyroid conditions run several times more common in women than men. TSH is the first test and is not the whole picture.
Cortisol and the stress axis. The signature is the mismatch: flattened at three in the afternoon, alert at eleven at night. Wired and tired describes a rhythm that has come out of phase rather than a hormone sitting high or low.
Sleep that looks adequate. Eight hours in bed and you wake wrecked. Sleep-disordered breathing presents differently in women than the textbook picture built on men, showing up as fatigue and low mood rather than obvious daytime sleepiness, and it gets attributed to hormones for years.
The cyclical one. If your tiredness arrives on a schedule, that is information. The luteal phase brings progesterone and its sedative metabolites, then withdraws them. In perimenopause the whole system stops being predictable, and the fatigue that comes with it has a different quality again.
Each of these has its own post on this site, and the taxonomy above links to them.
Normal does not mean no
One habit is worth building, and it is the through line of everything I write here.
A normal test result answers one question. It rarely answers the question you walked in with. Below, the six results most apt to end an investigation early, and what each one leaves open.
What That Result Does Not Rule Out
Six sentences you may have been told, and what each one leaves unanswered. Tap any.
What I would do with all of this
Take the number, not the word. If someone tells you your iron is fine, ask what your ferritin was. The figure is on the report. Both trials pointed at 50 as the level below which tired women improved, and a great many laboratories will print anything above their own lower limit without comment.
Bring a pattern rather than a feeling. Two weeks of notes: what time it hits, whether it tracks your cycle, whether sleep touches it, whether stairs have become a decision. A pattern survives a ten minute appointment. I am tired all the time does not.
Notice which kind you have. The six above want different investigations, and a woman who says I think this is the iron one, and here is why gets a different consultation than a woman who says she is exhausted.
And treat iron with respect rather than enthusiasm. Supplementing without knowing your ferritin is a poor idea, because too much iron carries its own problems and the excess has nowhere to go. Measure first. That is the whole point of this piece.
The thing underneath
Twenty-four years is the part I cannot put down.
The question was asked in 2001, in a major journal, by people who had done the work. The randomised trials followed. And the correction to the reference range arrived in 2025, which means an entire generation of women were handed an accurate result from a range that was set too low, and told there was nothing to find.
None of them were lying about being tired. The instrument was calibrated on a population that was already depleted, and it reported back that the depletion was ordinary.
Which is the same shape as almost everything else I write about here. The measurement was not neutral. Somebody decided what counted as normal, using a sample and a set of assumptions, and then the decision hardened into a number on a printout that nobody thought to question.
You are allowed to question it. Ask what the number was. Ask what the range was built from. Ask what the result rules out and what it leaves standing.
Everyone is tired is not a finding. It is the end of a conversation, and you are allowed to keep it going.
For the women reading
If you have been tired for months and were told your bloods were normal, ask for the ferritin figure. Not whether it was fine. The number. Both randomised trials in non-anaemic tired women found improvement below 50, and laboratory lower limits have historically sat a long way underneath that.
Work out which kind of tired you have before the appointment. Six mechanisms, six different tests, and the one thing that will not help is walking in with the word on its own.
None of this is medical advice, and no article knows your history. Do not start iron without measuring first. Fatigue also has causes this post does not cover, so anything sudden, severe, or accompanied by symptoms that frighten you belongs in front of a doctor rather than a blog.
Sources
- Vaucher, P., Druais, P.-L., Waldvogel, S., & Favrat, B. (2012). Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ, 184(11), 1247–1254. https://doi.org/10.1503/cmaj.110950
- Verdon, F., Burnand, B., Fallab Stubi, C.-L., et al. (2003). Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial. BMJ, 326(7399), 1124. https://doi.org/10.1136/bmj.326.7399.1124
- Rushton, D. H., Dover, R., Sainsbury, A. W., Norris, M. J., Gilkes, J. J. H., & Ramsay, I. D. (2001). Why should women have lower reference limits for haemoglobin and ferritin concentrations than men? BMJ, 322(7298), 1355–1357. https://doi.org/10.1136/bmj.322.7298.1355
- Sholzberg, M., Hillis, C., Crowther, M., & Selby, R. (2025). Diagnosis and management of iron deficiency in females. CMAJ, 197(24), E680–E687. https://doi.org/10.1503/cmaj.240570
- Dantzer, R., O'Connor, J. C., Freund, G. G., Johnson, R. W., & Kelley, K. W. (2008). From inflammation to sickness and depression: when the immune system subjugates the brain. Nature Reviews Neuroscience, 9(1), 46–56. https://doi.org/10.1038/nrn2297