Functional hypothyroidism, when normal values are not enough
For the woman who hears "your thyroid is fine" and still feels that something is off. And for everyone who wants to know what happens between the lab sheet and everyday life.
"Your thyroid is fine", and still something is off.
Sometimes it is not a drama.
No sudden collapse. No clear diagnosis. Rather something quiet. You get up in the morning and you are already tired. Your body feels heavy, although you slept enough. You feel cold faster than you used to. Your head runs slower, the drive is missing. Weight changes, not abruptly, rather creeping. Somewhere in the back of your mind there is this feeling: this is not how I usually know myself.
Then comes the doctor's appointment. Blood draw. A few days later the result. And the sentence so many people hear: "Your thyroid is fine. The TSH is within the normal range."
Objectively reassuring. Subjectively often confusing.
Because inwardly you feel something different. Your metabolism feels braked. Your energy is just enough for daily life. Your body acts as if someone had turned the dial down a notch. Not sick enough to actually be sick. But also not healthy enough to feel alive.
You are not imagining things. You are not being dramatic. What you experience often has a biological basis. And in a surprisingly large share of cases this basis has to do with a thyroid axis that, by classical reading, still works "normally", but is already running on the lowest flame.
This article is for you, if for months you have been trying to understand why something is missing that you cannot name. It is also for you, if you already have a Hashimoto diagnosis and ask yourself why you do not blossom under levothyroxine the way you wish. And it is for you, if you know the classical view of the thyroid and want to add what modern endocrinology, stress physiology and lifestyle medicine know in addition today.
We will go through this calmly. Without jargon. But with real depth.
What TSH, T4 and T3 mean, in everyday language.
To understand this dilemma, an image helps. Imagine your thyroid as a heating plant. It determines how much energy your body produces, how warm you feel, how fast your cells work, how active digestion, muscles and nervous system run.
For this plant to work, there are three central signals.
TSH, the thermostat from the brain.
TSH is not made in the thyroid. It comes from the pituitary, a small gland at the base of the brain. It is the thermostat of your metabolism. When the brain registers that thyroid effect in the body is dropping, TSH rises. It is a request to the thyroid to work more. If the demand falls, TSH is dialed down.
The decisive thing here: TSH does not measure the performance of the thyroid directly, it measures the regulatory pressure under which the thyroid stands. A higher TSH often means that the body has to pull harder to obtain sufficient effect.
T4, the storage hormone.
T4, or thyroxine, is the hormone that your thyroid mostly produces. You can imagine it like a raw material that still has to be activated. T4 itself only acts weakly. It is built to be converted in the body into the actual active form.
T3, the actual hormone.
T3, or triiodothyronine, is the truly active thyroid hormone. It acts directly in the cells and decides how fast energy is produced, how warm your body is, how awake your brain works, how active muscles, heart and digestion are.
And now it gets interesting. The major part of T3 does not arise in the thyroid, but through conversion from T4. This conversion happens above all in liver, gut, muscles and brain, through specific enzymes called deiodinases. These enzymes need selenium to work. And they are inhibited by stress hormones, chronic inflammation, sleep deprivation, and severe nutrient deficits.
This is exactly where the functional problem often begins.
The thyroid is not an isolated organ that either "runs" or "does not run". It is part of a regulatory chain that depends on brain, liver, gut, muscle and nervous system. When energy gets tight somewhere in this chain, your body lowers performance early. Not from defect, but from protection. The lab often sees this only late.
Three words that confuse everything: TSH, normal range, optimum.
Before we go deeper, let us sort out three terms. Because almost every frustration you experience with your thyroid values rests on a misunderstanding between these three words.
The TSH reference range is not a medical truth.
A reference range describes where about 95 percent of values lie in a studied population. Nothing more. It does not say where your individual metabolism functions best. It says what occurs in the majority of cases. Those are two very different things.
Typical TSH range in German labs: about 0.4 to 4.0 milli-units per liter. A value of 3.6 is "normal" by this measure. Your doctor nods, you nod, nobody asks the question whether your body still functions well in this zone or is already burning reserves to hold the value.
Taylor and colleagues published a comprehensive clinical review in 2013 in the Journal of Clinical Endocrinology and Metabolism on the consequences of small variations in thyroid function within the normal range.
Core finding: even fluctuations in the upper normal range can be associated with cardiovascular endpoints, metabolic changes, cognitive function and bone metabolism. The authors propose that the reference range be understood not as a biological truth, but as a statistical tool.
Taylor PN, Razvi S, Pearce SH, Dayan CM. A review of the clinical consequences of variation in thyroid function within the reference range. J Clin Endocrinol Metab. 2013;98(9):3562–3571. DOI: 10.1210/jc.2013-1315Why two people with the same TSH can feel completely different.
There are indications that every person has an individual set point, a kind of personal comfort zone for TSH. In a longitudinal study in which 16 healthy men were measured monthly for twelve months, the individual range of variation was about half as wide as the range of the whole group. If your personal set point were at about 1.2, then a TSH of 3.5 would not be neutral for your biology. For your neighbor, whose set point lies naturally at 3.0, the same value would be unremarkable. How far this concept can carry treatment decisions is still under professional discussion. You will find the study below in the sources.
The lab cannot see this. Your body can.
Álvarez-Pedrerol and colleagues studied 342 healthy four-year-old children from two Spanish birth cohorts in a cross-sectional study in 2007. All children had thyroid values within the normal range.
Core finding: children in the top TSH quartile of the normal range performed worse on cognitive tests and showed more attention symptoms. No association was found with T3, and a higher T4 was even linked to fewer attention symptoms. For context: this is a cross-sectional observation in four-year-olds. It shows an association, not a cause, and it cannot simply be transferred to adult women with exhaustion. The authors suggest re-examining the upper limit of the TSH reference range.
Álvarez-Pedrerol M, Ribas-Fitó N, Torrent M, et al. TSH concentration within the normal range is associated with cognitive function and ADHD symptoms in healthy preschoolers. Clin Endocrinol (Oxf). 2007;66(6):890–898. DOI: 10.1111/j.1365-2265.2007.02871.x"Within the normal range" does not automatically mean "optimal for you". It means: you are in the statistical majority. Whether your body still works well in this zone is a different question. And that question is not asked by your lab. You have to ask it.
A pattern I often encounter
People come with exhaustion, feeling cold, and a TSH in the upper normal range. In extended diagnostics several construction sites then often show up side by side, for example a low ferritin, a low vitamin D and positive TPO antibodies.
Whether ordering these construction sites changes the course cannot be proven in the individual case. It is the approach I consider sensible before hormone therapy is discussed. This is my clinical observation, not a body of evidence. And it is explicitly not a promise that things will go this way for you.
What functional hypothyroidism refers to.
The term describes a state in which your body suffers tangibly under a braked thyroid effect, while the classical lab values still lie within the reference range. Medicine sees: still normal. The person experiences: no longer properly supplied.
Technically, endocrinology distinguishes three stages. The manifest hypothyroidism with clearly elevated TSH and low fT4. The subclinical hypothyroidism with elevated TSH and still normal fT4. And the functional variant, which many people experience and which does not appear in the classical categories: a constellation in which all values lie "within the normal range", but the effect in the tissue, the well-being, the cell energy are no longer right.
According to the available surveys, women are affected more often than men. How large the difference is exactly varies considerably by region, age and definition, which is why I deliberately do not give a fixed ratio here.
Who is especially at risk
- Women in the postpartum period. After a birth a transient or lasting thyroid change can occur, especially with pre-existing TPO antibodies. How frequent this is is reported very differently depending on the survey.
- Women in perimenopause. Hormonal shifts, sleep loss and stress strain the thyroid axis especially strongly.
- People with Hashimoto in the family. Autoimmune diseases are partly hereditary, even if the triggers lie in lifestyle.
- People with chronic stress. A permanently elevated cortisol can inhibit the conversion of T4 to T3 and dampen the TSH response. This is well described above all in severe illness. Whether mild everyday stress does the same is not yet clarified.
- People with celiac disease or non-celiac gluten sensitivity. The association with Hashimoto is well documented.
- People with selenium, iodine, iron or vitamin D deficiency. Without raw materials, no stable production and no efficient conversion.
- People with a long-lasting calorie-deficit phase. Strict diets lower T3 conversion as a protective mechanism.
- Smokers, people with high pollutant burdens, people on certain medications. Various environmental factors can influence the axis.
A functional hypothyroidism is not a defect. It is often an early warning letter from your body that too many construction sites are open at the same time. Whoever takes this letter seriously can often regulate a great deal, before a manifest illness develops.
How a functional hypothyroidism can feel.
The symptoms are unspecific. No single sign proves anything. But if you find several of them in yourself, it is time to look more closely.
Energy and head.
"I am tired even though I slept." The exhaustion is not like after a strenuous week. It is structural. It feels as if the output of your inner motor was turned down. With it often a foggy head, slower thinking, less wit, less joy in things that used to be fun.
Biologically: in the cells, mitochondria and enzyme systems work with less T3 than they need to deliver full performance. You are producing energy, but at higher cost.
Body and metabolism.
Cold hands, cold feet, getting cold quickly. Slow digestion, constipation. Dry skin, brittle nails, diffuse hair loss. Creeping weight gain or difficulty losing weight despite stable nutrition. Muscles that no longer respond as they used to.
Mood and nervous system.
Inner coolness that feels like emotional distance. Irritability without clear cause. Increased anxiety or low mood that is not explained by the life situation. Reduced resilience under stress.
Hormone system and cycle.
Cycle irregularities. Stronger or longer periods. PMS that was not there before. Breast tenderness. Loss of libido. A wish for children that gets delayed without other graspable causes.
Many of these symptoms are dismissed as stress, overload or life phase. That is sometimes correct. But it is also often incomplete. Because stress and thyroid influence each other, and because one sometimes hides the other.
The invisible chapter: T4 to T3 and why conversion is so often the bottleneck.
Now comes a part for which there is rarely time in the ten-minute rhythm of a busy practice, but which is often important for functional complaints.
Your thyroid mainly produces T4. T4 is the raw material. The truly active substance that does the work in your cells is T3. And T3 arises to about 80 percent not in the thyroid, but outside. In liver, gut, muscle, brain. There the deiodinase enzymes convert T4 into T3. Exactly there it is decided how much thyroid effect actually arrives in your cells.
What slows this conversion.
The most common brakes
- Chronic cortisol. Chronic stress can shift the conversion of T4 toward reverse T3, a variant with very little effect of its own. This is described above all in severe illness. Whether mild everyday stress can trigger the same is not yet conclusively clarified.
- Inflammation. Chronic inflammatory stimuli, silent infections, metabolic syndrome, change deiodinase activity.
- Selenium deficiency. Without selenium, no functioning deiodinase. In the tissue, selenium is the lock that conversion needs.
- Iron deficiency. The enzyme thyroid peroxidase, which builds thyroid hormone, contains iron as a heme cofactor. With low iron, production can therefore become quieter.
- Zinc deficiency. Zinc is involved in receptor function and hormone effect.
- Permanently low calorie intake. Strict diets lower T3 production as an evolutionary protective mechanism. The body switches into a saving mode that only ramps back up after weeks to months.
- Sleep deprivation. There are indications that even moderate sleep deprivation can measurably change the thyroid axis. The evidence base for this is small, and in which direction this affects the effect in the tissue is open.
- Illness and trauma. Every severe illness, every operation, every longer infection temporarily depresses conversion and central regulation. This is described as the non-thyroidal illness syndrome.
Fliers and Boelen published a comprehensive review in 2021 on the non-thyroidal illness syndrome, that is, on the changes of the thyroid axis under chronic strain, illness or stress.
Core finding: under chronic strain the central TSH response sinks, deiodinase activity shifts, and the body produces preferentially reverse T3 instead of active T3. This is initially a protective mechanism. Under permanent strain, however, it becomes a trap, because the tissue ends up in a functional deficit despite seemingly normal hormone values.
Fliers E, Boelen A. An update on non-thyroidal illness syndrome. J Endocrinol Invest. 2021;44(8):1597–1607. DOI: 10.1007/s40618-020-01482-4If you have thyroid complaints and your TSH and fT4 are "normal", that does not mean everything is fine. It can be that the conversion in the tissues is the problem. And exactly this step is mostly not measured by the classical lab when the values are "normal".
The nutrients behind the scenes.
A thyroid can only work as well as its environment allows. And even the best hormone preparation only acts as well as the conversion and the receptors in your cells let it.
The relevant players
- Iodine. Building block of every thyroid hormone. In Germany the supply, according to recent surveys, is rather borderline. At the same time, too much iodine can be unfavorable in Hashimoto. With a known autoimmune thyroiditis, please do not take high-dose iodine preparations or iodine-rich algae products on your own. The dose belongs in medical hands.
- Selenium. Essential for the deiodinases and for the antioxidant glutathione peroxidase in thyroid tissue. In Hashimoto, several evaluations suggest that selenium can moderately lower TPO antibodies. The authors, however, rate the certainty of this evidence as very low.
- Iron and ferritin. The enzyme thyroid peroxidase contains iron. A low ferritin can therefore impair hormone formation. From which value a replenishment is sensible is judged differently in the field and depends on complaints, inflammatory status and cause. Please never take iron on suspicion. A workup belongs first, among other things the cause of the low ferritin, for example a bleeding source in the gastrointestinal tract, and the exclusion of an iron storage disease. If you take levothyroxine, iron preparations should be taken at least four hours apart, because iron can reduce the absorption of the hormone.
- Zinc. Involved in receptor and immune function.
- Vitamin D. Immunomodulator. In Hashimoto often markedly low, although the causality is not finally clarified. High-dose vitamin D over a longer period without monitoring can lead to overdose with elevated blood calcium. Dose and follow-up therefore belong in medical hands.
- B vitamins and magnesium. Relevant for energy and methylation metabolism.
- Sufficient protein. Transport proteins and enzymes are protein molecules. Chronic protein deficiency weakens the entire axis.
Wang and colleagues summarized six systematic reviews with a total of 75 randomized trials on selenium supplementation in autoimmune thyroiditis in 2023. Only one of the six reviews was of high methodological quality.
Core finding: a supplementation can moderately lower TPO antibodies after 3 and 6 months. The authors, however, rate the certainty of this evidence as very low under GRADE. After 12 months no difference remained. Whether this produces a noticeable difference in well-being is open. Lowering antibodies is not the same as feeling better.
Independently of this review the following applies: selenium has a narrow safety margin. A permanently high intake can be unfavorable, among other things a link with metabolic changes is discussed. A selenium administration therefore belongs time-limited, dosed and monitored, not in long-term self-medication.
Wang F, Li C, Li S, et al. Selenium and thyroid diseases. Nutrients. 2023;15(14):3194. DOI: 10.3390/nu15143194Shulhai and colleagues published a comprehensive review in 2024 on the role of nutrition in thyroid function.
Core finding: iodine, selenium, iron, zinc, vitamin D and B12 influence the production, conversion and effect of thyroid hormones. The gut axis plays an additional role, because part of T3 activation and the hormone cycle runs over gut and liver.
Shulhai AM, Rotondo R, Petraroli M, et al. The Role of Nutrition on Thyroid Function. Nutrients. 2024;16(15):2496. DOI: 10.3390/nu16152496Hashimoto: the most common invisible cause.
In iodine-sufficient countries, the by far most common cause of thyroid hypofunction is Hashimoto's thyroiditis, an autoimmune disease in which the immune system slowly attacks its own thyroid tissue. How high its share of primary hypothyroidism is exactly is reported differently depending on the survey.
The tricky thing about it: Hashimoto often begins quietly. TSH can be normal for years, while in the background TPO antibodies and TG antibodies rise and gradually inflame the tissue. Some people have elevated antibodies and no symptoms. Others have clear complaints with still normal hormone levels.
Weetman published an updated review in 2021 on the development of Hashimoto's thyroiditis.
Core finding: a genetic disposition in HLA class II, CTLA-4 and PTPN22 makes one susceptible. The disease can be triggered by iodine excess, selenium deficiency, certain infections, immunomodulating medications, and probably stress. A disturbance of the regulatory T cells leads to a loss of tolerance against the body's own tissue.
Weetman AP. An update on the pathogenesis of Hashimoto's thyroiditis. J Endocrinol Invest. 2021;44(5):883–890. DOI: 10.1007/s40618-020-01477-1Ludgate and colleagues published a review in 2024 in Nature Reviews Endocrinology on the connection between gut flora and thyroid disease.
Core finding: a dysbiosis, that is, an unfavorable shift in gut flora, can change immune tolerance and favor the risk of autoimmune thyroid disease. This is not yet a treatment concept, but a connection that should increasingly be taken seriously and considered in diagnostics and lifestyle.
Ludgate ME, Masetti G, Soares P. The relationship between the gut microbiota and thyroid disorders. Nat Rev Endocrinol. 2024;20(9):511–525. DOI: 10.1038/s41574-024-01003-wIf you have thyroid symptoms, TPO antibodies and an ultrasound belong to the basic workup, not only when TSH is "abnormal". A quiet Hashimoto changes the tissue long before it changes the hormone values. And it calls for a different overall strategy than a pure iodine deficiency.
Stress, cortisol and the hidden link to the thyroid.
The thyroid axis and the stress axis are not two independent systems. They talk to each other. And under chronic strain, the stress axis talks louder.
Under sustained stress, cortisol rises. As a model, cortisol can push in two ways. It can lower the release of TRH from the hypothalamus and thereby indirectly the TSH response. And it can shift T4 conversion in favor of the barely active reverse T3. The possible result: normal lab values, but a dampened effect in the tissue. Important for honesty: this coupling is physiologically plausible and described in animal experiments as well as in severe illness. In humans in everyday life it is not cleanly proven, and the study cited below precisely does not find the direct link between cortisol and TSH response.
Mokrani and colleagues examined in 2020, in 145 unmedicated depressed patients and 25 healthy controls, whether the thyroid and adrenal axes are linked.
Core finding: in the depressed group a flattened nighttime TSH release and at the same time an elevated cortisol activity were found. Both findings occurred side by side. The authors did not, however, find a direct link between the cortisol values and the TSH response. They explicitly conclude that an elevated cortisol does not explain the changes of the thyroid axis in depression. For me this means: the two systems evidently react together to strain, but the exact mechanism is open.
Mokrani MC, Duval F, Erb A, et al. Are the thyroid and adrenal system alterations linked in depression? Psychoneuroendocrinology. 2020;122:104831. DOI: 10.1016/j.psyneuen.2020.104831Zeng and colleagues investigated in 2023, in a large registry study with over four million people, the connection between stress-related diagnoses and autoimmune diseases including Hashimoto.
Core finding: there is a shared genetic architecture between stress-associated diagnoses and autoimmune thyroiditis. That does not mean stress causes Hashimoto. It means that stress is, in correspondingly disposed people, a relevant cofactor that should not be ignored.
Zeng Y, Suo C, Yao S, et al. Genetic Associations Between Stress-Related Disorders and Autoimmune Disease. Am J Psychiatry. 2023;180(4):294–304. DOI: 10.1176/appi.ajp.20220364The silent interaction: thyroid and female hormones.
The thyroid does not work in isolation. It stands in close connection with estrogen and progesterone. This relationship is fine, and it is bidirectional. A braked thyroid can influence the cycle. And a cyclic imbalance can dampen the thyroid further.
What happens with your hormones in functional hypothyroidism.
When thyroid performance drops, the hormonal milieu changes. The conversion of estrogen slows down in the liver. Estrogen can act longer and more strongly. Progesterone falls relatively into the background, not because suddenly too much estrogen is there, but because the counterweight becomes weaker. Exactly here often arises what many women experience as estrogen dominance.
Progesterone is especially sensitive. It only forms when a stable ovulation takes place. And a stable ovulation needs a calm, energy-able metabolic situation. A braked thyroid often means: later or unreliable ovulations, a second cycle half that feels unstable, more PMS, more breast tenderness, worse sleep in the luteal phase.
The binding problem: why estrogen distorts the lab values.
Estrogen raises the amount of thyroxine-binding globulin, abbreviated TBG, in the blood. That is the transport protein for thyroid hormone. When estrogen rises, for example in pregnancy, on the pill or in hormonal shifts, more hormone binds to TBG. The total amount in the blood then looks high. The free, active amount of hormone, however, can be lower than necessary.
The lab says: all within the normal range. The body feels: I am not getting going.
Bucci and colleagues published a review in 2022 on the role of thyroid autoimmunity in female infertility and reproductive medicine.
Core finding: thyroid hormones regulate menstruation, ovulation and implantation. Both manifest and subclinical hypothyroidism, especially in connection with TPO antibodies, are associated with cycle disorders, anovulation, miscarriages and reduced success in fertility treatment.
Bucci I, Giuliani C, Di Dalmazi G, et al. Thyroid Autoimmunity in Female Infertility and Assisted Reproductive Technology Outcome. Front Endocrinol (Lausanne). 2022;13:768363. DOI: 10.3389/fendo.2022.768363Mladenovic and colleagues published a clinical update in 2025 on the thyroid in pregnancy.
Core finding: in pregnancy the demand for thyroid hormone rises markedly, depending on the source by about 20 to 50 percent, with a peak between week 16 and 20. Estrogen raises TBG, hCG additionally stimulates the thyroid. Whoever is already working at the lower border can more easily land in a functional under-supply here. In manifest hypothyroidism in pregnancy, a good setting is important for mother and child according to current professional opinion. In subclinical constellations the evidence is less clear on whether a substitution can lower complications. This decision therefore belongs in the hands of gynaecology and endocrinology and not in a blog article.
Mladenovic V, Shah R, Medenica S, et al. Thyroid Gland and Pregnancy, Clinical Update. Horm Metab Res. 2025;57(5):303–314. DOI: 10.1055/a-2604-4177If you have cycle complaints, a wish for children, or you suffer from PMS, and you were told "thyroid fits", a second look is worth it. Not because every woman needs hormone therapy. But because functional fine-tuning often makes the difference exactly here.
Heart, vessels, metabolism: what subclinical values can mean in the long run.
The debate whether a subclinical hypothyroidism is cardiovascularly relevant has been running in endocrinology for two decades. The current state is more differentiated than the extremes.
Duntas and Wartofsky published a much-noticed review in Thyroid in 2007.
Core finding: subclinical hypothyroidism, especially with TSH over 10, is associated with unfavorable lipid values, impaired endothelial function, and elevated inflammation markers. In milder courses the data situation is less clear. The authors plead for an individual risk assessment instead of a rigid threshold.
Duntas LH, Wartofsky L. Cardiovascular risk and subclinical hypothyroidism: focus on lipids and new emerging risk factors. What is the evidence? Thyroid. 2007;17(11):1075–1084. DOI: 10.1089/thy.2007.0116Peng and colleagues published a meta-analysis in 2021 with over 21,000 patients.
Core finding: a levothyroxine therapy in subclinical hypothyroidism did not lower mortality in general. But in the subgroup of those under 65 to 70 years, therapy was associated with a markedly lower total and cardiovascular mortality. In older people no benefits showed up.
Peng CC, Huang HK, Wu BB, et al. Association of Thyroid Hormone Therapy with Mortality in Subclinical Hypothyroidism. J Clin Endocrinol Metab. 2021;106(1):292–303. DOI: 10.1210/clinem/dgaa777Zhong and colleagues published a systematic review in 2023 on older adults with subclinical hypothyroidism.
Core finding: in 13 cohorts with 44,514 adults from age 60, no significant rise in total mortality or cardiovascular events from a subclinical hypothyroidism showed up, not even with TSH over 10. That speaks against a routine hormone therapy in this age group.
Zhong J, Mu D, Zou Y, et al. High Thyrotropin Levels and Risk of Mortality in the Elderly With Subclinical Hypothyroidism. Endocr Pract. 2023;29(3):206–213. DOI: 10.1016/j.eprac.2022.11.011Subclinical hypothyroidism is in younger adults a relevant risk factor, in older people often a lab finding without hard clinical consequence. That means: a subclinical constellation in a 35-year-old woman with a wish for children deserves more attention than in a 78-year-old without complaints. Age is part of the therapy decision.
The honest counter-voice: what hormone therapy cannot deliver.
I want to speak very clearly here, because in parts of alternative medicine the impression sometimes arises that levothyroxine is the answer to every exhaustion with a slightly elevated TSH. It is not. And the best evidence is uncomfortable on this point.
Bekkering and an international guideline team published a guideline in the British Medical Journal in 2019, based on a systematic review of 21 randomized studies with 2,192 adults.
Core finding: a levothyroxine therapy in subclinical hypothyroidism showed in this synthesis no relevant advantage for quality of life, exhaustion, depressive symptoms or body weight. The guideline panel therefore issues a strong recommendation against hormone therapy in subclinical hypothyroidism. Explicitly excluded are women trying to become pregnant and people with a TSH above 20. For young adults up to about 30 years and for people with severe symptoms the recommendation may likewise not apply. I state this so clearly because it is the strongest counter-evidence to a quick hormone prescription.
Bekkering GE, Agoritsas T, Lytvyn L, et al. Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline. BMJ. 2019;365:l2006. DOI: 10.1136/bmj.l2006Good thyroid medicine is neither "quickly prescribe a hormone preparation" nor "categorically refuse". It is a careful weighing in the individual case. And it is open, when the first strategy does not work, to think onwards differently.
The path in my practice.
If you come into my practice with this topic, the setting is different from routine care. Not better, but financed differently and paced differently. I have more time per appointment. That time is the actual difference, not better knowledge.
The conversation
A good appointment with me begins with a thorough history. We talk about your story, your symptoms, your sleep, your nutrition, your cycle, your stress, previous pregnancies, medications, family autoimmune diseases. This conversation often takes half an hour to an hour. It is the most important diagnostic.
Physical examination and functional diagnostics
Beyond the classical examination, I use bioimpedance analysis, which can give indications of body composition and fluid distribution, and heart rate variability, which can say something about the activity of the autonomic nervous system. Both are supplementary follow-up values. They do not replace laboratory diagnostics and are not conclusive for the thyroid itself.
Targeted laboratory diagnostics
Not only TSH. And not only fT4. We look, when the situation requires it, at a broader profile that includes the conversion, the autoimmune component and the cofactors.
Special diagnostics as needed
Ultrasound of the thyroid, whole-blood micronutrient analysis, cycle hormone profile, gut diagnostics, when suspected also environmental factors like mold or heavy metal burden. Not for everyone. When the story suggests it.
The treatment decision
On this basis we decide together. In many cases the path begins with nutrition, sleep regulation, nutrient build-up and stress work. In other cases a hormone therapy is sensible from day one. Sometimes both in parallel. We define target values and follow up after eight to twelve weeks.
The thyroid lab in my practice
| Parameter | What it shows |
|---|---|
| TSH | Regulatory pressure from the pituitary |
| free T4 (fT4) | Hormone reserve in the blood |
| free T3 (fT3) | Active hormone, indicator of conversion |
| reverse T3, only in exceptional cases | Can be altered in severe illness or heavy strain. For diagnosing a thyroid hypofunction it is not suitable according to current professional opinion. I only order it when there is a concrete question behind it, and I explain beforehand what it cannot deliver. |
| TPO antibodies, TG antibodies | Autoimmune activity (Hashimoto) |
| Thyroglobulin | Thyroid mass and activity |
| Ferritin, transferrin saturation | Iron for hormone production |
| Selenium (whole blood), zinc | Cofactors for deiodinases |
| Vitamin D (25-OH) | Immunomodulator |
| Vitamin B12, folate | Blood formation, nerves |
| High-sensitivity CRP | Silent inflammation |
| HbA1c, fasting insulin | Metabolic state |
| Cycle hormones as needed | Estrogen, progesterone, prolactin |
This profile goes beyond the parameters that are usual within routine care. Whether the extra effort is sensible in the individual case depends on your history. Not every extended determination changes the treatment, and I discuss that openly with you beforehand.
The seven doctors of lifestyle for your thyroid axis.
For years I have been working with an image from my training in integrative medicine: the seven doctors of lifestyle. These are seven forces your body has at hand every day to regulate itself, when you let it.
For the thyroid they are especially important, because no hormone preparation can act sustainably when these forces are out of balance.
Nutrition that lowers inflammation and brings raw materials
Recent work argues for a Mediterranean orientation in Hashimoto, with lots of vegetables, good oil, legumes, fish and moderate meat. A small 2025 pilot randomized study found better antioxidant markers under a Mediterranean diet. The thyroid values and the antibodies did not change in any group. A gluten-free diet can be sensible in subgroups, but is not an automatism.
Sleep that regenerates your system
Sleep measurably intervenes in the regulation of the thyroid axis. A small randomized cross-over study with 30 adults found in 2024 that six weeks of mild sleep loss lowered TSH in women, while fT4 remained unchanged. In which direction this affects the effect in the tissue is open. What still holds: seven to eight hours, consistent rise times, morning light into the eyes, less screen in the evening. No esoterics. Biology.
Movement that carries instead of empties
Moderate, regular movement can support metabolism, insulin sensitivity and mood. Too much intense endurance sport without recovery can do the opposite in functional hypothyroidism. Strength training two to three times a week is today seen as favorable for the metabolic situation. If you have a heart condition, high blood pressure or an untreated marked hypofunction, please have the load medically cleared beforehand.
Breathing and nervous system training
A chronic sympathetic dominance can keep cortisol high and conversion low. Calm, slow belly breathing with a lengthened exhalation can address the parasympathetic system. In studies, regular breathing training was shown to be able to favorably influence heart rate variability. How strongly this works for you cannot be predicted. Ten calm minutes a day cost you little and can be a good start.
Warmth, light, grounding
People with functional hypothyroidism are often cold. Tend warmth actively. Warm foot baths, cherry stone pillows, ginger teas, morning sunlight. Sauna only if it agrees with you. With heart disease, cardiac arrhythmia, low or poorly controlled blood pressure, and in pregnancy, sauna belongs medically clarified beforehand. Anthroposophically speaking: a thyroid that has long lived only in the head needs contact with the body again.
Relationship and social regeneration
Chronic loneliness can raise inflammatory markers and stress hormones, that is well studied in psychoneuroimmunology. Whether this affects the thyroid axis in the individual case is not clarified. My experience is that people who feel supported find it easier to keep going. That is observation, not a body of evidence.
Meaning and inner rhythm
For what do you want to use your energy when it is back? My experience from the consultation: without a clear why, resolutions rarely hold long. With a clear why, keeping at it is easier. That is observation, not a body of evidence.
Petrov and colleagues evaluated in 2024 two randomized cross-over studies with 30 healthy adults in total, 20 of them women. They examined what six weeks of mild sleep loss do to thyroid parameters.
Core finding: in the women, TSH fell significantly, in the men it did not. Free T4 remained unchanged, and T3 and reverse T3 were not measured at all. What this means for the effect in the tissue is therefore open. The authors themselves file the finding under the heading of subclinical hyperthyroidism. The value of this small study lies above all in showing that sleep measurably intervenes in the regulation of the axis. In which direction is not yet clarified.
Petrov ME, Zuraikat FM, Cheng B, et al. Impact of sleep restriction on biomarkers of thyroid function: Two pooled randomized trials. Sleep Med. 2024;124:606–612. DOI: 10.1016/j.sleep.2024.10.035Laganà and colleagues published a twelve-week pilot randomized study in 2025 with 45 people with Hashimoto, 30 of them women, split into Mediterranean diet, gluten-free diet and free diet.
Core finding: in the Mediterranean group, markers of oxidative stress and the antioxidant reserve improved. A purely gluten-free diet did not show these effects. Just as important is what did not change: TSH, free T4 and Tg and TPO antibodies stayed the same in all three groups. The study is small and supports the focus on Mediterranean food rather than the reflexive omission of gluten. It permits no statement about well-being.
Laganà M, Piticchio T, Alibrandi A, et al. Effects of Dietary Habits on Markers of Oxidative Stress in Subjects with Hashimoto's Thyroiditis. Nutrients. 2025;17(2):363. DOI: 10.3390/nu17020363When the values are right and the well-being is not
A frequent question from people with Hashimoto on levothyroxine runs roughly like this: why have I not felt like myself since the diagnosis, even though the values are right? That is a legitimate question, and it rarely has a single answer.
What I look at in such situations is the environment of the hormone: cofactors such as iron, selenium, vitamin D and zinc, the cycle situation, sleep, strain and movement. Whether ordering these levels changes the course cannot be proven in the individual case, and there is hardly any research on it. I am explicitly describing a clinical approach here, not an expected result. Managing the dose remains in every case a medical decision with laboratory monitoring.
Hormone therapy is sometimes the beginning, not the end.
When a hormone therapy is indicated, it is good and important. But it is often only one building block. Whoever looks at the system without thinking about the cofactors, the autoimmune situation, the cycle, the stress axis and the lifestyle, gives away a lot of potential.
My philosophy in the practice: hormone, when needed. Cofactors, always. Lifestyle, always.
"My goal is not that you sit forever in my practice. My goal is that you are eventually so well regulated that you only need me selectively."
Your self-check.
This check does not replace a diagnosis. It is a tool with which you can take an honest stocktaking for yourself. If you nod at several points, it is a good moment to look more closely.
Block 1: body and metabolism
- You are often tired, although you sleep enough.
- You feel cold faster than others, have cold hands and feet.
- Your skin has become drier, your hair finer.
- Your nails are brittle.
- Your digestion has become more sluggish, constipation has increased.
- Weight shifts, although you do not eat substantially differently.
- Swellings on the face or legs are new.
Block 2: head and mood
- Your head is often foggy, concentration is harder.
- Your drive is braked, even for things you like.
- Low mood or irritability are new or stronger.
- Your sleep is less restful, although you lie down.
- You react more sensitively to stress than you used to.
Block 3: cycle, hormones, family
- Your cycle has become irregular or your periods stronger.
- You have PMS, breast tenderness or shortened luteal phases.
- Your wish for children is delayed without a clear other cause.
- You have Hashimoto, autoimmune diseases or thyroid problems in the family.
- You were recently pregnant, gave birth, or are currently in menopause.
- You take the pill or hormonal IUD and feel a change.
Block 4: lab and history so far
- Your TSH was rated as "normal" although you have symptoms.
- fT3 or TPO antibodies have not been measured so far.
- You already take levothyroxine and do not feel well despite "good values".
- You have so far only received reduced diagnostics and feel something is missing.
These points are deliberately unspecific, because that is exactly the problem: they can point to the thyroid, but just as well to anaemia, lack of sleep, a depressive episode, an infection, a heart or kidney disease, or something else entirely.
If several of them have persisted for weeks and limit you in everyday life, that is no proof of a thyroid problem. It is a reason to have it medically clarified what lies behind it. Please do not derive your own diagnosis from this and do not start self-treatment.
Frequent questions, honestly answered.
Three concrete next steps.
Observe yourself for a week
A few notes are enough. When are you awake, when drained? How is your temperature? Your sleep? Your mood? Your cycle? A week of attentive listening teaches you more about your body than five lab tests without context.
Get a more complete lab
Please do not ask only for TSH. Under clinical suspicion, have at least TSH, fT4, fT3 and TPO antibodies measured together. If your family practice does not consider these determinations necessary, ask for the reason. Often there is a good one. If afterwards you still feel that something is missing, you can get a second opinion.
Have your values explained
"All normal" is no explanation. You have a right to understand what your numbers mean in your specific life. If you need time and depth for that, I offer it to you in my consultation.
You are not alone with what you feel. You are not crazy because you know there is more. You are simply someone who does not look away. That is rare. And it is strong.
Sources and further reading
- Biondi B, Cappola AR, Cooper DS. Subclinical Hypothyroidism: A Review. JAMA. 2019;322(2):153–160. DOI: 10.1001/jama.2019.9052
- Bekkering GE, Agoritsas T, Lytvyn L, et al. Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline. BMJ. 2019;365:l2006. DOI: 10.1136/bmj.l2006
- Taylor PN, Razvi S, Pearce SH, Dayan CM. A review of the clinical consequences of variation in thyroid function within the reference range. J Clin Endocrinol Metab. 2013;98(9):3562–3571. DOI: 10.1210/jc.2013-1315
- 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):1068–1072. DOI: 10.1210/jcem.87.3.8165
- Álvarez-Pedrerol M, Ribas-Fitó N, Torrent M, et al. TSH concentration within the normal range is associated with cognitive function and ADHD symptoms in healthy preschoolers. Clin Endocrinol (Oxf). 2007;66(6):890–898. DOI: 10.1111/j.1365-2265.2007.02871.x
- Kim YA, Park YJ. Prevalence and risk factors of subclinical thyroid disease. Endocrinol Metab (Seoul). 2014;29(1):20–29. DOI: 10.3803/EnM.2014.29.1.20
- Duntas LH, Wartofsky L. Cardiovascular risk and subclinical hypothyroidism: focus on lipids and new emerging risk factors. What is the evidence? Thyroid. 2007;17(11):1075–1084. DOI: 10.1089/thy.2007.0116
- van Tienhoven-Wind LJ, Dullaart RPF. Low-normal thyroid function and novel cardiometabolic biomarkers. Nutrients. 2015;7(2):1352–1377. DOI: 10.3390/nu7021352
- Peng CC, Huang HK, Wu BB, et al. Association of Thyroid Hormone Therapy with Mortality in Subclinical Hypothyroidism. J Clin Endocrinol Metab. 2021;106(1):292–303. DOI: 10.1210/clinem/dgaa777
- Zhong J, Mu D, Zou Y, et al. High Thyrotropin Levels and Risk of Mortality in the Elderly With Subclinical Hypothyroidism. Endocr Pract. 2023;29(3):206–213. DOI: 10.1016/j.eprac.2022.11.011
- Biondi B, Cappola AR. Subclinical hypothyroidism in older individuals. Lancet Diabetes Endocrinol. 2022;10(2):129–141. DOI: 10.1016/S2213-8587(21)00285-0
- Taylor PN, Medici MM, Hubalewska-Dydejczyk A, Boelaert K. Hypothyroidism. Lancet. 2024;404(10460):1347–1364. DOI: 10.1016/S0140-6736(24)01614-3
- Chaker L, Papaleontiou M. Hypothyroidism: A Review. JAMA. 2025. DOI: 10.1001/jama.2025.13559
- Weetman AP. An update on the pathogenesis of Hashimoto's thyroiditis. J Endocrinol Invest. 2021;44(5):883–890. DOI: 10.1007/s40618-020-01477-1
- Ludgate ME, Masetti G, Soares P. The relationship between the gut microbiota and thyroid disorders. Nat Rev Endocrinol. 2024;20(9):511–525. DOI: 10.1038/s41574-024-01003-w
- Fliers E, Boelen A. An update on non-thyroidal illness syndrome. J Endocrinol Invest. 2021;44(8):1597–1607. DOI: 10.1007/s40618-020-01482-4
- Shulhai AM, Rotondo R, Petraroli M, et al. The Role of Nutrition on Thyroid Function. Nutrients. 2024;16(15):2496. DOI: 10.3390/nu16152496
- Wang F, Li C, Li S, et al. Selenium and thyroid diseases. Nutrients. 2023;15(14):3194. DOI: 10.3390/nu15143194
- Bath SC. Thyroid function and iodine intake: global recommendations and relevant dietary trends. Nat Rev Endocrinol. 2024;20(8):474–486. DOI: 10.1038/s41574-024-00983-z
- Bucci I, Giuliani C, Di Dalmazi G, et al. Thyroid Autoimmunity in Female Infertility and Assisted Reproductive Technology Outcome. Front Endocrinol (Lausanne). 2022;13:768363. DOI: 10.3389/fendo.2022.768363
- Mladenovic V, Shah R, Medenica S, et al. Thyroid Gland and Pregnancy, Clinical Update. Horm Metab Res. 2025;57(5):303–314. DOI: 10.1055/a-2604-4177
- Sankoda A, Suzuki H, Imaizumi M, et al. Effects of Levothyroxine Treatment on Fertility and Pregnancy Outcomes in Subclinical Hypothyroidism. Thyroid. 2024;34(4):519–530. DOI: 10.1089/thy.2023.0546
- Peng CC-H, Pearce EN. An update on thyroid disorders in the postpartum period. J Endocrinol Invest. 2022;45(8):1497–1506. DOI: 10.1007/s40618-022-01762-1
- Mokrani MC, Duval F, Erb A, et al. Are the thyroid and adrenal system alterations linked in depression? Psychoneuroendocrinology. 2020;122:104831. DOI: 10.1016/j.psyneuen.2020.104831
- Zeng Y, Suo C, Yao S, et al. Genetic Associations Between Stress-Related Disorders and Autoimmune Disease. Am J Psychiatry. 2023;180(4):294–304. DOI: 10.1176/appi.ajp.20220364
- Petrov ME, Zuraikat FM, Cheng B, et al. Impact of sleep restriction on biomarkers of thyroid function. Sleep Med. 2024;124:606–612. DOI: 10.1016/j.sleep.2024.10.035
- Laganà M, Piticchio T, Alibrandi A, et al. Effects of Dietary Habits on Markers of Oxidative Stress in Subjects with Hashimoto's Thyroiditis. Nutrients. 2025;17(2):363. DOI: 10.3390/nu17020363
- Wu K, Zhou Y, Ke S, et al. Lifestyle is associated with thyroid function in subclinical hypothyroidism. BMC Endocr Disord. 2021;21(1):112. DOI: 10.1186/s12902-021-00772-z
- Jonklaas J, Bianco AC, Cappola AR, et al. Evidence-Based Use of Levothyroxine/Liothyronine Combinations in Treating Hypothyroidism. Thyroid. 2021;31(2):156–182. DOI: 10.1089/thy.2020.0720