Quick answer: TSH (thyroid-stimulating hormone) is made by the pituitary gland and tells the thyroid how much hormone to make. It is usually the first thyroid test. High TSH typically means the thyroid is underactive (hypothyroidism); low TSH typically means it is overactive (hyperthyroidism). TSH is best read with free T4 and, when needed, free T3 and thyroid antibodies.
Key takeaways
TSH is made by the pituitary gland and tells the thyroid how much hormone to produce.
A high TSH usually points to an underactive thyroid, while a low TSH usually points to an overactive one.
TSH is best read together with free T4 and, when needed, free T3 and thyroid antibodies.
What is TSH?
TSH is a pituitary hormone. When thyroid hormone is low, TSH rises to push the thyroid harder; when thyroid hormone is high, TSH falls.
Why TSH matters
TSH screens for thyroid disease and monitors thyroid medication, and it reflects the brain-thyroid feedback loop.
Understanding your result
Reference ranges vary by lab, age and sex. Your provider interprets your result against the lab’s range and your overall picture, rather than chasing a single number. Functional labs are optional. They can be helpful in more complex cases.
What low TSH can mean
A low TSH can mean hyperthyroidism, including Graves’ disease, or too much thyroid medication. Rarely, it points to pituitary problems.
What high TSH can mean
A high TSH can mean hypothyroidism, including Hashimoto’s, or recovery from illness. It can also reflect not enough thyroid medication, or iodine deficiency.
What affects TSH
TSH is affected by time of day (higher at night and early morning), illness and stress, biotin supplements, and age and pregnancy.
Ways to support healthy levels
- Eat enough protein and calories; very low-calorie dieting can slow thyroid hormone activation
- Get iodine from food such as seafood, dairy and iodized salt, but avoid high-dose iodine supplements unless prescribed
- Selenium (Brazil nuts, seafood), zinc and iron support thyroid hormone production and conversion
- Manage stress and sleep
- Take thyroid medication as prescribed and retest as your doctor advises
What does the research show about TSH?
The NHANES III survey measured thyroid blood tests in a nationally representative sample of 17,353 Americans aged 12 and older. Among people without known thyroid disease, average TSH was 1.50 mIU/L, and TSH ran higher in women, rose with age, and differed by ethnic background. About 4.6% of the population had biochemical hypothyroidism, most of it mild (4.3%), and 1.3% had hyperthyroidism. A limitation is that it was a single snapshot, so it shows how common abnormal results are but not what happens to people over time. (Hollowell et al., 2002)
A pooled analysis of 11 prospective cohorts combined individual data on 55,287 adults followed for a total of 542,494 person-years. Compared with normal thyroid function, a TSH of 10 to 19.9 mIU/L was linked with a higher risk of coronary heart disease events (hazard ratio 1.89) and coronary death (hazard ratio 1.58), while milder elevations carried little or no extra risk, and total mortality was not higher. Because these were observational studies, they show an association rather than proof that TSH itself causes heart disease. (Rodondi et al., 2010)
The TRUST trial randomly assigned 737 adults aged 65 and older with persistently mild TSH elevations (4.60 to 19.99 mIU/L, with normal free T4) to thyroid hormone, at a typical dose of 50 micrograms a day, or to placebo. After one year, TSH fell to an average of 3.63 mIU/L with thyroid hormone versus 5.48 mIU/L with placebo, but hypothyroid symptom scores and tiredness scores did not differ between the groups. The trial enrolled older adults with mostly mild elevations, so the results may not apply to younger people or to higher TSH levels. (Stott et al., 2017)
Taken together, these studies suggest that a mildly high TSH is common, especially with age, and that its meaning depends on how high it is, the free T4 result and the whole clinical picture.
TSH and healthy aging
Thyroid hormones set the pace of metabolism in nearly every cell and directly influence mitochondria, the energy factories of the cell. Thyroid function and autoimmunity both change with age, so keeping an eye on thyroid health supports energy, heart health and healthy weight over time.
Related thyroid tests: free T4, free T3, reverse T3, TPO antibodies, thyroglobulin antibodies.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have fatigue, weight change, feeling cold or hot, hair loss or constipation, or anxiety, palpitations or tremor. The same is true if you have irregular periods or trouble conceiving, a family history of thyroid disease, or abnormal thyroid results you want explained.
See a medical provider promptly for a racing or irregular heartbeat, severe confusion or drowsiness, a rapidly growing neck lump, or trouble swallowing or breathing.
TSH at a glance
| Topic | What the article explains |
|---|---|
| Why it matters | Screens for thyroid disease; monitors thyroid medication; and reflects the brain-thyroid feedback loop |
| What can affect it | Time of day (higher at night and early morning); illness and stress; biotin supplements; and age and pregnancy |
| Supportive habits discussed | Eat enough protein and calories; very low-calorie dieting can slow thyroid hormone activation; get iodine from food such as seafood, dairy and iodized salt, but avoid high-dose iodine supplements unless prescribed; selenium (Brazil nuts, seafood), zinc and iron support thyroid hormone production and conversion; manage stress and sleep; and take thyroid medication as prescribed and retest as your doctor advises |
Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Should we add free T4, free T3 and antibodies to my TSH to get a complete picture?
What might my TSH be telling us, given my health history and symptoms?
Which other labs would be worth pairing with my TSH to get a clearer picture?
When would it make sense to recheck my TSH, and what could I work on in the meantime?
Frequently asked questions
What does high TSH mean?
Usually an underactive thyroid.
What does low TSH mean?
Usually an overactive thyroid or too much medication.
Is TSH enough to check my thyroid?
It is a good screen, but free T4, free T3 and antibodies add detail when symptoms persist.
Does TSH change during the day?
Yes. It is usually higher in the early morning.
Sources
- Bianco AC, et al. Paradigms of Dynamic Control of Thyroid Hormone Signaling. Endocr Rev 2019. PMID: 31033998. https://pubmed.ncbi.nlm.nih.gov/31033998/
- Hollowell JG, et al. Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J Clin Endocrinol Metab 2002. PMID: 11836274. https://pubmed.ncbi.nlm.nih.gov/11836274/
- Leung AM, et al. Consequences of excess iodine. Nat Rev Endocrinol 2014. PMID: 24342882. https://pubmed.ncbi.nlm.nih.gov/24342882/
- Li D, et al. Association of Biotin Ingestion With Performance of Hormone and Nonhormone Assays in Healthy Adults. JAMA 2017. PMID: 28973622. https://pubmed.ncbi.nlm.nih.gov/28973622/
- Rodondi N, et al. Subclinical hypothyroidism and the risk of coronary heart disease and mortality. JAMA 2010. PMID: 20858880. https://pubmed.ncbi.nlm.nih.gov/20858880/
- Russell W, et al. Free triiodothyronine has a distinct circadian rhythm that is delayed but parallels thyrotropin levels. J Clin Endocrinol Metab 2008. PMID: 18364382. https://pubmed.ncbi.nlm.nih.gov/18364382/
- Stott DJ, et al. Thyroid Hormone Therapy for Older Adults with Subclinical Hypothyroidism. N Engl J Med 2017. PMID: 28402245. https://pubmed.ncbi.nlm.nih.gov/28402245/
- Van den Berghe G. Non-thyroidal illness in the ICU: a syndrome with different faces. Thyroid 2014. PMID: 24845024. https://pubmed.ncbi.nlm.nih.gov/24845024/
- Ventura M, et al. Selenium and Thyroid Disease: From Pathophysiology to Treatment. Int J Endocrinol 2017. PMID: 28255299. https://pubmed.ncbi.nlm.nih.gov/28255299/
- MedlinePlus: TSH (Thyroid-Stimulating Hormone) Test
- NIDDK: Thyroid Tests
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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