Thyroid levels normal, still exhausted
Why “within the normal range” is a statistical statement and not a statement about you. About the reference range, the individual set point, fT3, fT4, reverse T3 and antibodies.
“Your levels are fine” is a sentence about a table. It is not a sentence about you. A reference range describes what occurs frequently in a large group. It does not describe where your own metabolism runs well.
I would like to tell you something right at the beginning that many people never hear: if your lab work is unremarkable and you still feel exhausted, you are not a difficult case. You are an ordinary case. Because between “statistically unremarkable” and “optimal for this person” there is a space that a single number cannot map.
This article explains why that is. It explains what TSH does well and what it cannot do. And it names just as clearly where the science ends today and where my clinical experience begins. Keeping those two apart matters more to me than giving a smooth answer.
What this article covers
- How a reference range comes about and what it is not
- The individual set point and why it is largely innate
- What TSH measures and what it does not measure
- fT4, fT3 and the question of conversion
- Reverse T3: what is documented and what is not
- Antibodies and their link with the symptom burden
- Iron, selenium, iodine and vitamin D as building blocks of the system
- Why some people stay symptomatic on hormone therapy
- What besides the thyroid can be behind exhaustion
- Three concrete levers for your next medical appointment
How I label the evidence
Clinical study Randomised trials or meta-analyses in humans. The strongest informative value.
Human observation Cohorts, cross-sectional studies, registry data. They show associations, not causes.
Animal model In vivo data from animal studies. Biologically plausible, not automatically transferable to humans.
Cell level In vitro data. They explain mechanisms, they do not prove a clinical effect.
Three times “everything is normal” and you stop trusting yourself
The sentence “everything is normal” and what it can set off
I know this pattern very well. It is not a single story but an account that reaches me again and again in different variations. It usually sounds roughly like this.
There is a tiredness that has been there for months. Not dramatic, more of a functioning tiredness. The day can be managed, but the engine idles. Often added to that: a different feel to hair and skin, being constantly colder than everyone else in the room, and a head that needs longer for sentences that used to simply be there.
Blood is drawn. The report comes back: everything normal. Sometimes this repeats in a second and a third practice. And at some point what this sentence sets off internally begins to change. Disappointment turns into shame.
What I describe here is explicitly only a temporal and experienced connection, as it is often reported to me. I cannot derive causality from it, and I cannot derive any statement about you from it either. It is an observation from conversations, not a finding and not a study result.
I also write this without any reproach towards anyone. Physicians who reassure after an unremarkable TSH are acting correctly from a professional point of view. A TSH within the reference range is a reassuring finding, and screening with TSH is well founded. What can easily get lost in that short sentence, though, is a distinction that is medically relevant: the difference between the range of a population and the point of a single person.
I am not claiming that the thyroid is the explanation in your case. I am only saying: “normal” is information about a distribution and not about your experience. And your experience is information that does not have to be argued away.
What happens biologically in that moment is, by the way, not nothing. Repeated experiences of “I am not being believed” put a strain on the nervous system and can change the stress course over weeks. People who do not feel taken seriously go back later, describe less, ask fewer questions. A diagnostic gap turns into a relationship gap. And that can genuinely get in the way of diagnostics.
You are not oversensitive because you are not satisfied with “everything is normal”. You have asked a legitimate question that a single laboratory value simply cannot answer completely.
The better question is not: “Is my value normal?” It is: “Is my value normal for me, and what is still missing from the picture?”
And now you know why that sentence can feel so empty, even though it is meant kindly.
How a reference range comes about and what it really says
Imagine a sports hall with a thousand people. Blood is drawn from everyone. Everyone says of themselves that they are healthy. The results are sorted by size. Then the lowest 2.5 percent are cut off at the bottom and the highest 2.5 percent at the top. What remains is the reference range. That is essentially how it comes about.
That is a clever procedure. It makes laboratories comparable and protects against overdiagnosis. But it has two built-in properties worth knowing. First: the range describes the group, not the individual. Second: it is as wide as the group scatters, and the scatter between people is large for thyroid values.
Human observation A research group around Stig Andersen in Denmark drew blood from 16 healthy men every month for twelve months and measured TSH, T4 and T3 each time.
What they observed: each man oscillated around his own, very narrow mean. The individual span was roughly half as wide as the span of the group. The authors call this personal mean the set point.
What this means for you: a result within the laboratory limits is not automatically normal for you. It can be clearly shifted for your own set point without ever touching a limit.
Andersen S, Pedersen KM, Bruun NH, Laurberg P. J Clin Endocrinol Metab. 2002;87(3):1068-72. DOI: 10.1210/jcem.87.3.8165Human observation A Danish twin study compared almost 700 twin pairs from the national twin register and looked at how similar identical and fraternal pairs are in their thyroid values.
Result: about 64 percent of the variation in TSH and around 65 percent of the variation in fT4 and fT3 could be traced back to genetic factors.
What this means for you: your personal set point is largely innate. It is a characteristic of yours, like your shoe size. And it does not become your value simply because it lies within the range of everyone else.
Hansen PS, Brix TH, Sørensen TIA, Kyvik KO, Hegedüs L. J Clin Endocrinol Metab. 2004;89(3):1181-7. DOI: 10.1210/jc.2003-031641Two people can have the same TSH. For one of them it is their usual point. For the other it is a doubling of their own baseline that still never crosses a laboratory limit.
On top of that comes a practical level that is rarely mentioned: TSH fluctuates over the course of the day. A very large analysis of more than 465,000 measurements showed that the upper limit of TSH moves depending on time of day, age and sex, among other things because of the nocturnal TSH rise. Someone measured early in the morning while fasting tends to get a different value than in the late morning.
Human observation Joel Ehrenkranz and colleagues analysed 465,593 TSH measurements and almost 113,000 fT4 measurements from people without known thyroid disease.
Observation: the lower limit of TSH stayed stable across the day, the upper limit rose with age from 6.45 to 7.55 mIU/l, mainly through an increasing nocturnal TSH peak. Sex and origin also influenced the values measurably.
What this means for you: the time of your blood draw can be part of the picture. For follow-up checks it can make sense to always measure at the same time of day.
Ehrenkranz J, Bach PR, Snow GL et al. Thyroid. 2015;25(8):954-61. DOI: 10.1089/thy.2014.0589From “everyone has a set point” it does not follow that “everyone needs hormones”. That is exactly the false conclusion I want to warn about. The set point explains why a normal value can be shifted for you. It does not prove that it is, and in a single person without earlier measurements it cannot be reconstructed.
That is why the practically most valuable sentence of this section may be this one: a value is a snapshot. Two values weeks apart are a line. And a line often says more than any limit.
And now you know why “normal” is a group term and not a personal statement.
What TSH does well and what it cannot see
TSH is not a thyroid hormone. That surprises many people. TSH is the command from above. The pituitary gland looks at how much hormone arrives in the blood and calls louder or more quietly accordingly. Little hormone, louder call, high TSH. A lot of hormone, quieter call, low TSH.
An image for it: TSH is the accelerator pedal, not the speed. It tells you how hard the foot is pressing. It does not tell you whether the car is actually moving, whether there is fuel in the tank and whether the wheels have contact with the road.
The hypothalamus sends TRH
The hypothalamus in the brain gives the superordinate signal. With a strong energy deficit, long illness or persistent stress, this signal can be dampened.
The pituitary gland answers with TSH
It reacts extremely sensitively. Even small changes in the amount of hormone in the blood lead to a logarithmically amplified TSH response. That makes TSH a good screening value.
The thyroid produces mainly T4
Around 80 percent of the production is T4, the storage hormone. It needs iodine as raw material and thyroid peroxidase as a tool. This enzyme is a heme enzyme and needs iron.
The tissue converts T4 into T3
Only T3 docks at the cell nucleus and steers energy production, warmth, heart rate and metabolism. The deiodinases responsible for this are selenium enzymes. This is where it is decided what actually arrives.
The decisive place is therefore further down, in the tissue. And that is exactly where TSH does not look. It is an excellent sensor for the control loop between brain and gland. It is not a sensor for the conversion in the muscle cell, in the liver or in the nervous system.
What TSH does well
- Very sensitive for over- and underactivity of the gland
- Established first screening value, broadly standardised
- Good control parameter for dose finding under hormone therapy
- Inexpensive, available everywhere, easily comparable
What TSH does not show
- How much T4 is actually converted into active T3
- Whether an autoimmune reaction against the thyroid is running
- Whether iodine, iron and selenium are available as building blocks
- Whether your personal set point is shifted
- Whether there is a disturbance above the gland, that is, a central one
TSH is not a bad value. It is precise for exactly one question. The problem only arises when the answer to one question is turned into the answer to all questions.
Put differently: a normal TSH rules out a relevant underactive thyroid very reliably. It does not rule out that something else in your metabolism is stuck.
And now you know why a single value from above cannot say what arrives below.
fT4, fT3 and reverse T3: the picture gets bigger
If symptoms persist, it is worth looking at the hormones themselves. fT4 is the free storage hormone. fT3 is the free active hormone. And then there is a third variant that is much debated: reverse T3.
With T4, the body has a switch point. It can turn it into the active T3. Or it can turn it into rT3, a kind of mirror image that fits the same receptor but does not switch it on. In images: a key that goes into the lock and does not turn. This switch point is not a malfunction. It is an energy-saving mode.
Human observation Greet Van den Berghe from Leuven summarised the data on non-thyroidal illness syndrome, that is, on the thyroid values of severely ill people in intensive care units.
Observation: typical are a low T3, a low to low-normal T4 and an elevated reverse T3, without the TSH rising. Among the reasons are shifted activities of the type 1 and type 3 deiodinases. Part of this shift is explicitly interpreted as a sensible adaptation to food restriction, not as a defect.
What this means for you: a low T3 with a high rT3 can be an energy-saving mode of the body and not the cause of your symptoms. The right question is then: what is the body currently saving on?
Van den Berghe G. Thyroid. 2014;24(10):1456-65. DOI: 10.1089/thy.2014.0201In outpatient practice I see reverse T3 as a piece of the puzzle, not as proof. The good evidence on it comes predominantly from intensive care medicine and from situations with severe illness or pronounced energy deficit. For everyday life with mild exhaustion there are no robust studies showing that an rT3-guided approach produces better outcomes. The professional societies accordingly do not recommend rT3 as a routine value.
I write this explicitly because I would rather be honest than impressive. When I do look at rT3, I look at it as one of several observations, in connection with nutrition, sleep, inflammation and strain. Not as a switch to be turned.
Why fT3 is a question in its own right
The conversion of T4 into T3 is apparently not equally effective in everyone. This can be seen most clearly in people who no longer have a thyroid of their own and therefore receive T4 exclusively as a tablet.
Human observation Damiano Gullo and colleagues from Catania compared 1,811 people without a thyroid of their own on pure T4 therapy with a normal TSH against 3,875 comparison persons with their own thyroid.
Observation: despite a normal TSH, the fT4 values of those treated were significantly higher on average and the fT3 values significantly lower. More than 20 percent were outside the range of the comparison group with fT3 or fT4. The ratio of fT3 to fT4 scattered strongly between individuals.
What this means for you: the ability to make active T3 out of T4 differs greatly between individuals. A normal TSH does not prove that the supply in the tissue looks the same as in someone with a healthy gland.
Gullo D, Latina A, Frasca F, Le Moli R, Pellegriti G, Vigneri R. PLoS One. 2011;6(8):e22552. DOI: 10.1371/journal.pone.0022552Many people think of the gland when they think of the thyroid. The more interesting place, though, is the cell. The gland mainly produces a raw material. What becomes of it is decided in the liver, muscle, fatty tissue and brain.
That is why, in my view, the thyroid is not an organ question but a metabolic question. And metabolism depends on building blocks, sleep, inflammatory status and energy balance.
And now you know why a second and third value sometimes brings more contour into the picture.
Antibodies: when the immune system is already involved
TPO antibodies are directed against thyroid peroxidase, that is, against exactly the enzyme your body needs for hormone production. Detecting them does not automatically mean disease. It means: the immune system is occupied with this organ.
Human observation The US population survey NHANES III measured TSH, T4 and thyroid antibodies in 17,353 people aged 12 and over.
Observation: TPO antibodies were detectable in about 11.3 percent, thyroglobulin antibodies in 10.4 percent. Both were more frequent in women and increased with age. A mild underactivity was found in 4.3 percent of the population, an overt one in 0.3 percent.
What this means for you: positive antibodies are common and, taken by themselves, not a verdict. They are, however, a sign that the course can change over the years and that check-ups can make sense.
Hollowell JG, Staehling NW, Flanders WD et al. J Clin Endocrinol Metab. 2002;87(2):489-99. DOI: 10.1210/jcem.87.2.8182Human observation Johannes Ott and colleagues from Vienna examined 426 women with normal thyroid function before thyroid surgery and compared antibody levels with a symptom questionnaire and quality of life.
Observation: women with TPO antibodies above the calculated threshold reported 6.7 symptoms on average, the comparison group 4.1. TSH practically did not differ between the groups. More frequently named were persistent tiredness, dry hair, inner restlessness and irritability.
What this means for you: symptom burden and hormone levels do not appear to measure the same thing. The authors conclude that an underactive thyroid is only one partial factor in the symptoms. That is an observation and not proof of a cause, but it matches much of what I hear.
Ott J, Promberger R, Kober F et al. Thyroid. 2011;21(2):161-7. DOI: 10.1089/thy.2010.0191Clinical study Tim Korevaar and colleagues jointly analysed three Dutch birth cohorts with a total of 11,212 pregnant women and investigated from which antibody level effects become measurable.
Observation: a dose-dependent association appeared between TPO antibody level, TSH, fT4 and the risk of preterm birth. Even women with antibody values below the manufacturer's cut-off already had an increased risk. The authors consider the usual cut-offs to be set too high.
What this means for you: with antibodies too, the cut-off is a statistical construct. A result just below the limit does not necessarily mean “no issue”, especially not when trying to conceive or during pregnancy.
Korevaar TIM, Pop VJ, Chaker L et al. J Clin Endocrinol Metab. 2018;103(2):778-789. DOI: 10.1210/jc.2017-01560“A cut-off is an agreement, not a constant of nature. It can help us with decisions. It does not describe the biology of an individual person.”
Shukri Jarmoukli, ViveCura BerlinAnd now you know why, with persistent symptoms, I like to know whether the immune system is playing a part.
The building blocks behind the values: iron, selenium, iodine, vitamin D
Now comes the part that interests me most clinically. Because the thyroid is a small factory. And a factory without raw materials and without tools produces less, no matter how loudly the management floor calls.
Lens metabolism
Iodine is the raw material. Iron is the tool: thyroid peroxidase is a heme enzyme and needs iron to work at all. If iron is missing, hormone production can be slowed at the cell level long before an anaemia becomes visible.
Lens immune system
Hydrogen peroxide, an aggressive molecule, is created during hormone production. Selenium-dependent glutathione peroxidases defuse it. If selenium is missing, oxidative stress in the tissue can rise, which plays a role in the discussion about autoimmunity.
Lens hormonal system
The deiodinases that convert T4 into T3 are also selenium enzymes. So the conversion depends on the same trace element as the protection against oxidative stress. Two tasks, one resource.
Lens nervous system
T3 steers energy production in the mitochondria, in the brain as well. Chronic stress can dampen the thyroid axis via the superordinate signals. Exhaustion and thyroid are therefore rarely cleanly separable.
Human observation Margaret Rayman from the University of Surrey summarised the data on iodine, iron and selenium in autoimmune thyroid disease.
Observation: iron deficiency can impair thyroid metabolism, because thyroid peroxidase only becomes active after binding heme. People with autoimmune thyroiditis more often have iron deficiency, among other reasons through autoimmune gastritis and coeliac disease as accompanying conditions. It is also described that in two thirds of women with persistent symptoms despite a suitable hormone dose, raising ferritin above 100 micrograms per litre went along with an improvement in symptoms.
What this means for you: if you are tired and your values are fine, the ferritin level can be a very worthwhile second look. That is a value that can simply be measured.
Rayman MP. Proc Nutr Soc. 2019;78(1):34-44. DOI: 10.1017/S0029665118001192Animal model A Chinese research group examined in pregnant rats what happens when iron deficiency is present without anaemia.
Observation: both forms of iron deficiency led to lowered thyroid hormone levels from the middle of pregnancy onwards. The activity of thyroid peroxidase fell measurably, and it did so before the iron in the liver dropped.
What this means for you: the mechanism is well documented in the animal model. In humans it is biologically plausible and supported by observations, but not proven with the same certainty. I therefore deliberately formulate it as a hypothesis with a good foundation.
Hu X, Teng X, Zheng H et al. Nutr Res. 2014;34(7):604-12. DOI: 10.1016/j.nutres.2014.06.007Clinical study A Danish research group around Johanna Wichman summarised 16 controlled studies on selenium in chronic autoimmune thyroiditis in a meta-analysis.
Observation: in people on hormone therapy, TPO antibodies fell clearly after three months and stayed lower after six and twelve months. In newly diagnosed, untreated individuals the effect appeared after three months, after that not consistently. The quality of the evidence was rated as low overall, and side effects occurred more frequently in the selenium group.
What this means for you: selenium can lower antibody titres. Whether that translates into feeling better is explicitly still open. And more is not better: selenium has a narrow therapeutic window.
Wichman J, Winther KH, Bonnema SJ, Hegedüs L. Thyroid. 2016;26(12):1681-1692. DOI: 10.1089/thy.2016.0256Clinical study Hui Jiang and colleagues summarised six randomised studies with a total of 258 people with Hashimoto's thyroiditis on vitamin D supplementation.
Observation: TPO antibodies fell significantly in the vitamin D group. TSH, fT3 and fT4, by contrast, did not change measurably.
What this means for you: vitamin D appears to play a role on the immunological level rather than on the hormonal one. From a lowered antibody value it does not automatically follow that you feel better. That is a difference I consider important.
Jiang H, Chen X, Qian X, Shao S. J Clin Pharm Ther. 2022;47(6):767-775. DOI: 10.1111/jcpt.13605And now you know why, with “normal values”, I like to also look at the raw materials.
When treatment is given and the symptoms remain
There is one group that has a particularly hard time: people with a confirmed underactive thyroid, a well-adjusted TSH and nevertheless persistent symptoms. This is not a marginal phenomenon. It is a recognised topic in the specialist literature.
Clinical study An American group around Mohamed Shakir carried out a randomised, double-blind cross-over study with 75 people with an underactive thyroid. Each of them went through T4 alone, T4 plus T3 and desiccated thyroid extract in sequence, 22 weeks each.
Observation: looking at the whole group, there were no differences in symptoms, quality of life, memory tests and mood. In the subgroup of the most burdened third, by contrast, a clear preference for the combinations with T3 appeared, with better values in several questionnaires.
What this means for you: for most people, T4 alone is entirely sufficient. For a subgroup it could be different. This question belongs in a careful medical conversation, not in self-medication.
Shakir MKM, Brooks DI, McAninch EA et al. J Clin Endocrinol Metab. 2021;106(11):e4400-e4413. DOI: 10.1210/clinem/dgab478Human observation Heleen Jansen and colleagues from Amsterdam compiled in a review how difficult it is to attribute symptoms in thyroid disease.
Observation: in a large population survey, people with a mildly elevated TSH reported a similar number of thyroid-typical complaints as people with a healthy thyroid, and the TSH level had no influence on the symptom score. At the same time the authors describe that in about a third of treated individuals an attempt to stop the medication succeeded without an underactive thyroid appearing.
What this means for you: a mildly elevated TSH does not reliably explain symptoms statistically. And a therapy once started is not necessarily lifelong in every case. Both argue for care in both directions.
Jansen HI, Boelen A, Heijboer AC, Bruinstroop E, Fliers E. Front Endocrinol. 2023;14:1130661. DOI: 10.3389/fendo.2023.1130661Human observation Bernadette Biondi, Anne Cappola and David Cooper summarised the state of knowledge on mild underactivity in JAMA.
Observation: up to 10 percent of adults are affected. TSH rises with age even without thyroid disease, which leads to the frequency in people over 70 being overestimated. Treatment can make sense from a TSH of 10 mIU/l upwards, as well as in younger and middle-aged people with matching symptoms. For people aged 65 and over there is no documented benefit.
What this means for you: age changes the interpretation of the same value. What is conspicuous at 35 can be age-appropriate at 75.
Biondi B, Cappola AR, Cooper DS. JAMA. 2019;322(2):153-160. DOI: 10.1001/jama.2019.9052The functional view does not lead to treating more. It leads to looking more closely before treating. And to allowing the possibility that the thyroid is not the explanation.
More diagnostics is not automatically better medicine. But more targeted diagnostics can prevent someone going home for years with “everything is normal”, even though the decisive question was never asked.
And now you know why I say “it depends” so often on this topic.
What else besides the thyroid can be behind it
Now comes the most honest section of this article. Because it would be convenient to put everything down to the thyroid. Convenient, but wrong. Exhaustion is an unspecific signal. It has many possible senders.
What I always keep in mind with persistent exhaustion
- Iron deficiency without anaemia, recognisable only through ferritin and transferrin saturation, not through the blood count
- Vitamin D deficiency, particularly common at our latitudes from October to March
- Sleep quality, especially non-restorative sleep and sleep apnoea, which often goes unnoticed for years
- The cortisol curve across the day, which can flatten under persistent strain
- Blood sugar swings and a beginning insulin resistance
- Silent inflammation, for example with gut topics, dental foci or chronic infections
- Depressive episodes and anxiety disorders, which can show up physically first
- Coeliac disease and other autoimmune conditions, which occur together more often than by chance
- Environmental burdens, for example mould exposure or heavy metals
- Medications that can influence the absorption or conversion of thyroid hormones
And there is one more direction that is rarely considered: a value can carry meaning at the upper end as well. In the Rotterdam Study it appeared that higher fT4 values, even within the normal range, went along with a higher cardiovascular risk.
Human observation Layal Chaker and colleagues followed 9,233 participants of the Rotterdam Study over a median of 8.8 years and calculated the ten-year risk of cardiovascular mortality along the percentiles of TSH and fT4.
Observation: fT4 values above the 90th percentile went along with a calculated ten-year risk above 7.5 percent. In men above the 97th percentile it was 10.8 percent. The authors suggest defining optimal ranges in future according to disease risk and not only according to distribution.
What this means for you: the idea that “somewhere in the range” is equally good cannot be maintained. Within the same reference range there can be more favourable and less favourable zones. The authors explicitly emphasise that the results need to be replicated.
Chaker L, Korevaar TIM, Rizopoulos D et al. J Clin Endocrinol Metab. 2017;102(8):2853-2861. DOI: 10.1210/jc.2017-00410Energy is not a luxury. Energy is the material that relationships, work and joy are made of. Someone without energy does not lose a symptom. They lose room to move in their own life.
That is why I think it is wrong to dismiss chronic tiredness as a mere sensitivity. And I think it is just as wrong to assign it a single cause, only so that there finally is one. Both routes shorten the same person.
And now you know why I prefer to think broadly rather than assign quickly.
Three levers you can use from tomorrow
I am not giving you recipes here. Therapy emerges after a medical history and not after a blog article. What I can give you are three tools that can change your next medical appointment.
Ask for your numbers, not only for the assessment
You have a right to your findings. Ask for the concrete values with units and the laboratory's corresponding reference ranges, not only for the sentence “it was fine”. File them in a simple table, with the date and time of the blood draw. After two or three measurements you see a line instead of a point. That line is the closest you can get to your personal set point.
Keep a simple symptom log for two weeks
Note down daily, in thirty seconds: energy from 1 to 10, feeling cold yes or no, digestion, sleep quality, mood. That sounds banal and it is not. It turns a diffuse “I feel bad” into a pattern that can be discussed. Physicians can work with patterns far better than with snapshots, and you get your own perception back as a data point.
Ask a more precise question
Instead of “Is my thyroid all right?” you can ask: “My TSH is normal. In my situation, would fT4, fT3, TPO antibodies and ferritin additionally make sense, and if not, why not?” This question is respectful, concrete and answerable. It opens a conversation instead of ending it. And it shows that you are not looking for a diagnosis but for an explanation.
The most important step is not the next laboratory value. It is the moment in which you stop mistrusting yourself. Your body is reporting something. That report is information, not a character flaw.
It may be that in the end the thyroid is not the answer at all. Even then you have lost nothing. You have then carefully ruled out one cause and stand at the beginning of the next question, instead of in the fog.
And now you know why I believe that good diagnostics starts with a better question and not with more blood tubes.
Frequently asked questions
What does it mean if my TSH is normal but I still feel exhausted?
A normal TSH first of all means only this: your value lies within the span measured in 95 percent of a reference population. That is a statistical statement, not a statement about your well-being.
Studies on the variation of thyroid values show that every person has a very narrow range of their own, the so-called set point. The range of a single person is roughly half as wide as the range of the group. A result can therefore lie within the laboratory limits and still be shifted for that one person.
At the same time: exhaustion is unspecific and can have many other causes. Taking both seriously is more useful than settling prematurely on one explanation.
Is TSH alone enough to assess the thyroid?
For a first screening, TSH is a very good and very sensitive value. The pituitary gland responds to even small changes in the amount of hormone with an amplified answer.
As a single value it has limits, though. It describes the control from above, not the supply in the tissue. It says nothing about how much T4 is actually converted into the active T3, whether an autoimmune reaction is running or whether the building blocks for hormone production are available.
With persistent symptoms it can therefore make sense to also look at fT4, fT3 and the antibodies. Whether that is indicated in your case is decided in a medical conversation.
What is the difference between a reference range and an individual optimum?
The reference range is a statistical construct. A large group of apparently healthy people is measured, then 2.5 percent are cut off at the top and 2.5 percent at the bottom. What remains is called normal.
The individual optimum is something else: the point at which your own metabolism runs well. Twin studies show that the regulation of the thyroid axis is roughly two thirds genetically determined. Your optimum is therefore largely innate and lies somewhere within that wide group span.
That is why the same number can be completely relaxed for one person and already a clear shift for another. From a single measurement, however, the personal set point cannot be reconstructed. That requires a course over time.
Which thyroid values make sense when the TSH is normal?
If symptoms persist, a wider picture can help: fT4 as the storage hormone, fT3 as the active hormone, TPO antibodies and thyroglobulin antibodies as a sign of autoimmune involvement, and depending on the situation reverse T3.
In my view the building blocks of the system belong to that as well: ferritin, selenium, zinc, vitamin D and iodine status. An ultrasound examination can show structural changes that do not appear in the blood.
Which of these examinations make sense in an individual case belongs in a medical conversation and not in a blanket list. More diagnostics is not automatically better diagnostics.
What does reverse T3 tell us?
Reverse T3 is an inactive variant of the thyroid hormone. The body can convert T4 either into the active T3 or into this inactive rT3. In images, rT3 is a key that fits the lock and does not turn.
In severe illness, in intensive care and under pronounced energy deficit, the ratio shifts measurably towards rT3, with a low T3 at the same time. The technical term is non-thyroidal illness syndrome. Part of this shift is today understood as a sensible energy-saving mode of the body, not as a defect.
In outpatient symptoms the informative value of rT3 is contested and it is not recommended as a routine value by the professional societies. I see it as one piece of the puzzle among many, not as proof and not as a switch to be turned.
What do TPO antibodies mean when the thyroid values are normal?
TPO antibodies indicate that the immune system is occupied with the thyroid. They are directed against exactly the enzyme the body needs for hormone production.
In the large US population survey NHANES III they were detectable in about 11 percent of those examined, clearly more often in women and increasing with age. So they are common and, taken by themselves, not a verdict.
An Austrian study of more than 400 women found: women with high TPO antibodies reported considerably more symptoms on average and a lower quality of life, at practically the same TSH as the comparison group. That is an observation and not proof of a cause. It can, however, be a reason why check-ups over time can be worthwhile.
Which nutrients does the thyroid need?
Three building blocks are particularly well studied. Iodine is the raw material of the hormone. Iron is needed because the key enzyme of hormone production, thyroid peroxidase, is a heme enzyme and cannot work without iron. Selenium is a component of the enzymes that convert T4 into T3 and that defuse the hydrogen peroxide created during hormone production.
A review on nutrition and the thyroid describes that in two thirds of women with persistent symptoms despite a suitable hormone dose, raising ferritin above 100 micrograms per litre went along with an improvement in symptoms.
Self-treatment on suspicion can do harm, especially with iodine and selenium. Too much iodine can set off an autoimmune reaction, selenium has a narrow therapeutic window. Measuring before taking is the better order.
Why do some people stay symptomatic on levothyroxine even though the TSH is right?
A large Italian analysis of more than 1,800 people without a thyroid of their own showed: on pure T4 and with a normal TSH, the fT4 values were higher on average and the fT3 values lower than in comparison persons with their own thyroid. More than 20 percent were outside the range of the comparison group with fT3 or fT4.
The ability to convert T4 into T3 is apparently distributed very differently. In a randomised comparison study there was no difference for the group as a whole between T4 alone, T4 plus T3 and desiccated thyroid extract. In the most burdened third, however, there was a clear preference for the combination.
For most people, T4 alone is therefore entirely sufficient. For a subgroup it could be different. This is a conversation that belongs in the hands of the treating physician, not a question for self-medication.
From what point is an elevated TSH considered in need of treatment?
The current specialist literature is relatively clear here: from a TSH of 10 mIU/l upwards, the benefit of treatment outweighs the risks according to today's data.
Between the upper reference value and 10, the decision is made individually, among other things according to age, antibody status, wish to have children, cardiovascular risk and symptoms. In people over 65, restraint is advisable, because TSH rises physiologically with age and over-treatment carries risks of its own.
In mild forms, waiting and monitoring often comes first, because some of the values settle again on their own. This overview does not replace a medical decision, it only describes the frame.
Can the time of the blood draw influence my TSH?
Yes, and this is rarely mentioned. TSH follows a daily rhythm with a nocturnal peak and lower values over the course of the morning.
In an analysis of more than 465,000 measurements, the lower limit of the reference range stayed stable across the day, while the upper limit moved between 6.45 and 7.55 mIU/l depending on age. The main reason was the nocturnal TSH rise increasing with age.
In practical terms this means: for follow-up checks it can make sense to always measure at roughly the same time of day. Otherwise you may end up comparing apples with pears.
What else besides the thyroid can be behind the exhaustion?
A great deal, and honesty requires saying so. Iron deficiency without anaemia, vitamin D deficiency, a dysregulated cortisol curve, sleep apnoea, non-restorative sleep, chronic inflammation, blood sugar swings, depressive episodes, long COVID, silent infections and environmental burdens.
A review on attributing symptoms in thyroid disease explicitly emphasises that the complaints with a mildly elevated TSH are statistically hard to distinguish from those of people with a healthy thyroid.
The thyroid is one possible factor. It is rarely the only one. A good work-up therefore looks broadly and not only at one organ.
Is the functional view a contradiction to standard endocrinology?
No, and I would like to emphasise that explicitly. The endocrinological guidelines and cut-offs have been carefully developed and protect many people from unnecessary treatment. TSH screening is one of the most efficient examinations we have.
What a functional or integrative view adds is the question about the conditions behind it: building blocks, conversion, immune system, sleep, strain. That does not replace classical diagnostics, it widens it by further perspectives.
I consider it important not to build up fronts here. Colleagues who work according to guidelines are acting correctly. I see my task as asking additional questions when the guideline does not explain the symptoms.
Read on in the thyroid guide
- Functional hypothyroidism: when normal values are not enough
- Understanding Hashimoto's thyroiditis: why the immune system attacks the thyroid
- The thyroid and female hormones: the underestimated interplay
- Iron deficiency and the thyroid as sleep thieves
- Heavy metals and Hashimoto: the thyroid connection
Where this topic touches other areas
The thyroid never stands alone. If you recognised yourself in this article, it is often worth looking at the neighbouring systems as well.
Ferritin level: what is really normal?
The same reference range question, applied to a value that is often decisive with exhaustion.
IronIron deficiency, tiredness and exhaustion
Why iron deficiency can cost energy long before an anaemia appears.
StressCortisol and the HPA axis in burnout
How the stress axis can dampen the superordinate signals of the thyroid.
HormonesHormonal imbalance in women
Thyroid, cycle and adrenal gland are a networked system, not a side-by-side arrangement.
NutrientsVitamin D deficiency: why the sun is not enough in winter
The nutrient with the strongest immunological connection to the thyroid.
ExhaustionChronic fatigue: when your body pulls the plug
When exhaustion remains even though every single value is unremarkable.
GutLeaky gut, intestinal permeability and zonulin
The gut barrier as one of the places where autoimmunity is discussed.
ContextAdrenal fatigue: myth and facts
An example of how I handle concepts that are popular but weakly supported.
Sources
All references were checked via PubMed and linked with a DOI. The study type is given in square brackets so that you can judge the informative value yourself.
- Andersen S, Pedersen KM, Bruun NH, Laurberg P. Narrow individual variations in serum T4 and T3 in normal subjects: a clue to the understanding of subclinical thyroid disease. J Clin Endocrinol Metab. 2002;87(3):1068-72. DOI: 10.1210/jcem.87.3.8165 [Real-world longitudinal study, n=16, 12 months]
- Hollowell JG, Staehling NW, Flanders WD, Hannon WH, Gunter EW, Spencer CA, Braverman LE. Serum TSH, T4, and thyroid antibodies in the United States population (1988 to 1994): NHANES III. J Clin Endocrinol Metab. 2002;87(2):489-99. DOI: 10.1210/jcem.87.2.8182 [Real-world population study, n=17,353]
- Hansen PS, Brix TH, Sørensen TIA, Kyvik KO, Hegedüs L. Major genetic influence on the regulation of the pituitary-thyroid axis: a study of healthy Danish twins. J Clin Endocrinol Metab. 2004;89(3):1181-7. DOI: 10.1210/jc.2003-031641 [Real-world twin study, n=690 pairs]
- Ehrenkranz J, Bach PR, Snow GL, Schneider A, Lee JL, Ilstrup S, Bennett ST, Benvenga S. Circadian and circannual rhythms in thyroid hormones: determining the TSH and free T4 reference intervals based upon time of day, age, and sex. Thyroid. 2015;25(8):954-61. DOI: 10.1089/thy.2014.0589 [Real-world analysis, n=465,593 measurements]
- Biondi B, Cappola AR, Cooper DS. Subclinical hypothyroidism: a review. JAMA. 2019;322(2):153-160. DOI: 10.1001/jama.2019.9052 [Review, JAMA]
- Jansen HI, Boelen A, Heijboer AC, Bruinstroop E, Fliers E. Hypothyroidism: the difficulty in attributing symptoms to their underlying cause. Front Endocrinol (Lausanne). 2023;14:1130661. DOI: 10.3389/fendo.2023.1130661 [Review]
- Ott J, Promberger R, Kober F, Neuhold N, Tea M, Huber JC, Hermann M. Hashimoto's thyroiditis affects symptom load and quality of life unrelated to hypothyroidism: a prospective case-control study in women undergoing thyroidectomy for benign goiter. Thyroid. 2011;21(2):161-7. DOI: 10.1089/thy.2010.0191 [Real-world case-control study, n=426]
- Korevaar TIM, Pop VJ, Chaker L, Goddijn M, de Rijke YB, Bisschop PH, Broeren MA, Jaddoe VWV, Medici M, Visser TJ, Steegers EAP, Vrijkotte TG, Peeters RP. Dose dependency and a functional cutoff for TPO-antibody positivity during pregnancy. J Clin Endocrinol Metab. 2018;103(2):778-789. DOI: 10.1210/jc.2017-01560 [Meta-analysis of individual data, n=11,212]
- Gullo D, Latina A, Frasca F, Le Moli R, Pellegriti G, Vigneri R. Levothyroxine monotherapy cannot guarantee euthyroidism in all athyreotic patients. PLoS One. 2011;6(8):e22552. DOI: 10.1371/journal.pone.0022552 [Real-world cohort, n=1,811 vs. 3,875]
- Shakir MKM, Brooks DI, McAninch EA, Fonseca TL, Mai VQ, Bianco AC, Hoang TD. Comparative effectiveness of levothyroxine, desiccated thyroid extract, and levothyroxine plus liothyronine in hypothyroidism. J Clin Endocrinol Metab. 2021;106(11):e4400-e4413. DOI: 10.1210/clinem/dgab478 [RCT, double-blind, crossover, n=75]
- Van den Berghe G. Non-thyroidal illness in the ICU: a syndrome with different faces. Thyroid. 2014;24(10):1456-65. DOI: 10.1089/thy.2014.0201 [Mechanism review]
- Rayman MP. Multiple nutritional factors and thyroid disease, with particular reference to autoimmune thyroid disease. Proc Nutr Soc. 2019;78(1):34-44. DOI: 10.1017/S0029665118001192 [Review, nutrition]
- Hu X, Teng X, Zheng H, Shan Z, Li J, Jin T, Xiong C, Zhang H, Fan C, Teng W. Iron deficiency without anemia causes maternal hypothyroxinemia in pregnant rats. Nutr Res. 2014;34(7):604-12. DOI: 10.1016/j.nutres.2014.06.007 [In vivo, rat]
- Wichman J, Winther KH, Bonnema SJ, Hegedüs L. Selenium supplementation significantly reduces thyroid autoantibody levels in patients with chronic autoimmune thyroiditis: a systematic review and meta-analysis. Thyroid. 2016;26(12):1681-1692. DOI: 10.1089/thy.2016.0256 [Meta-analysis, k=16 studies]
- Zuo Y, Li Y, Gu X, Lei Z. The correlation between selenium levels and autoimmune thyroid disease: a systematic review and meta-analysis. Ann Palliat Med. 2021;10(4):4398-4408. DOI: 10.21037/apm-21-449 [Meta-analysis, k=17, n=1,911]
- Jiang H, Chen X, Qian X, Shao S. Effects of vitamin D treatment on thyroid function and autoimmunity markers in patients with Hashimoto's thyroiditis: a meta-analysis of randomized controlled trials. J Clin Pharm Ther. 2022;47(6):767-775. DOI: 10.1111/jcpt.13605 [Meta-analysis, k=6 RCTs, n=258]
- Chaker L, Korevaar TIM, Rizopoulos D, Collet TH, Völzke H, Hofman A, Rodondi N, Cappola AR, Peeters RP, Franco OH. Defining optimal health range for thyroid function based on the risk of cardiovascular disease. J Clin Endocrinol Metab. 2017;102(8):2853-2861. DOI: 10.1210/jc.2017-00410 [Real-world cohort, n=9,233]
- Calissendorff J, Falhammar H. To treat or not to treat subclinical hypothyroidism, what is the evidence? Medicina (Kaunas). 2020;56(1):40. DOI: 10.3390/medicina56010040 [Review]