Thyrotropin, or thyroid-stimulating hormone (TSH) is the primary hormone produced by the pituitary gland to regulate the thyroid. Lab-designated normal TSH levels fall between 0.5 and 5.0 mIU/L (milli-international units per liter), but this range is not a one-size-fits-all number.
TSH levels in a blood sample are used to assess thyroid function. Certain conditions like hypothyroidism, pregnancy, thyroid cancer, pituitary gland disease, and even older age alter your TSH levels.
Working with hundreds of patients with thyroid disease, we have found that TSH levels alone are insufficient to gain a complete diagnostic picture. Let’s take a look at everything you need to know about TSH levels and what other tests may be necessary to understand how your thyroid is functioning.
Colorado residents: Tired of seeking comprehensive care to heal your thyroid? Our providers spend 1-2 hours with patients per appointment. We’ll help you understand what you can do to reverse your issues at the root.
What Do TSH Levels Tell You?
TSH levels are one indication of how well the thyroid gland is functioning. The thyroid plays a large role in overall body function, and thyroid disorders often cause disruptive health symptoms.
What is the thyroid gland responsible for? Thyroid hormones affect virtually every organ in your body. Your thyroid plays a significant role in regulating your body’s metabolism, mood, heart health, reproductive health, energy production, and bone maintenance.
Your thyroid hormone levels and other targeted diagnostic tests can give your healthcare providers a path to diagnosing and treating both underactive thyroid conditions and overactive thyroid conditions.
Normal TSH Levels
While the conventionally accepted normal range for TSH levels is between 0.5 and 5.0 mIU/L, your age and sex can influence levels. TSH levels will also fluctuate during pregnancy and even seasonally throughout the year.
In addition, functional medicine practitioners like us prefer patients to have TSH levels between 0.5-2.5, as this is the range that indicates optimal thyroid function. The National Academy of Clinical Biochemistry released data indicating that more than 95% of normal individuals have a TSH level below 2.5 mlU/L.
TSH Levels by Age
This table is a handy guide to determining the accepted TSH level for a given age group.
| Age Group | Lab TSH Range (mIU/L) | Notes |
| Newborns (0-4 days) | 1.0-39.0 | High range due to birth surge. |
| Infants (2-20 weeks) | 1.7-9.1 | Gradually narrows to adult levels. |
| Children (5-14 years) | 0.7-6.4 | Approaching adult TSH levels. |
| Adults (20+ years) | 0.4-4.0 | May vary slightly by lab, sex, and specific age range; keep in mind that 2.6-4.0 is suboptimal. |
| Elderly (65+ years) | Variable, often slightly higher | Upper limit may be 4.5 – 6.0 mIU/L. |
TSH Levels by Sex
The average TSH levels for women are:
- 18-29 years old: 0.4-2.34 mlU/L
- 30-49 years old: 0.4-4.0 mlU/L
- 50-79 years old: 0.46-4.68mlU/L
The average TSH levels for men are slightly higher than for women:
- 18-50 years old: 0.5-4.15 mIU/L
- 51-70 years old: 0.5-4.59 mIU/L
- 71-90 years old: 0.4-5.49 mlU/L
Estrogen has a notable impact on TSH levels, and overall thyroid function, mainly through its influence on thyroid hormone-binding proteins and the metabolism of thyroid hormones.
Estrogen increases the levels of TBG, a protein that binds to thyroid hormones in the blood. When TBG levels rise, more thyroid hormones are bound and not free to act on the body’s tissues. This decrease in free thyroid hormones (like Free T3 and T4) can lead the thyroid to produce more hormones.
TSH Levels During Pregnancy
During pregnancy, estrogen levels rise significantly. This increase in estrogen leads to higher TBG levels, which can affect thyroid hormone levels and TSH. This is why TSH reference ranges during pregnancy are different.
The level of thyroid hormones during each pregnancy trimester, according to The American Endocrine Society, are as follows:
- First Trimester: 0.1-2.5 mIU/L
- Second Trimester: 0.2-3.0 mIU/L
- Third Trimester: 0.3-3.5 mIU/L
According to a study published in 2019, women with a TSH level over 2.5 were at significantly higher risk of having a miscarriage, with that risk going up dramatically when TSH was over 4.8. With this in mind, we prefer all of our patients, especially female patients who are trying to conceive or are pregnant, to have a TSH between 0.5-2.5. Studies like this show us that the body operates at its best when TSH is within a tighter range.
It is important to note that TSH ranges can be specific to each person and that different laboratories will have slightly different reference ranges.
Your TSH levels can fall within the normal range and you can still have noticeable symptoms. If you are experiencing symptoms such as unexplained weight gain or weight loss, goiters, or an inability to control your body temperature, functional healthcare providers like ours at PrimeHealth can help you find relief.
Read Next: Natural Remedies for Hypothyroidism
Testing Your Level of TSH
Experiencing symptoms of hypothyroidism, symptoms of hyperthyroidism, having a history of thyroid disease, or frequent miscarriages are good reasons to move forward with a TSH test.
This simple blood test measures your TSH levels and doesn’t require any special preparation like fasting. You’ll need to refrain from taking the supplement biotin (vitamin B7), as it can interfere with test results.
What levels of TSH are concerning? Levels outside the normal reference range are especially concerning, and subclinical levels may cause concern if accompanied by related symptoms. Low TSH levels below 0.4mIU/L mean you are producing too much thyroid hormone, while high TSH levels over 4.0mIU/L indicate you are not producing enough thyroid hormone.
Even sub-optimal TSH levels that are between 2.5-4 will prompt functional medicine providers to do further investigation as to what might be compromising thyroid function. This allows us to address them and prevent worsening thyroid function down the road.
Depending on your TSH test results, further testing or actions may need to be taken. This table is a quick reference for interpreting your TSH value:
| TSH Level (mIU/L) | Potential Interpretation | Suggested Actions/Considerations |
| < 0.4 | Possible Hyperthyroidism (Overactive Thyroid) | Further testing (like Free T4, Free T3), clinical evaluation for hyperthyroidism symptoms. |
| 0.5 – 2.5 | Optimal | Considered the optimal range in functional medicine |
| 2.6 – 4 | Non-optimal but “within normal range” (“lab-normal”) | Further testing and evaluation are necessary from a Functional Medicine standpoint. Conventional doctors will most likely say this is “normal.” |
| > 4.0 – 10.0 | Mild or Subclinical Hypothyroidism | Monitor and retest soon. Treatment depends on symptoms and clinical context. Further testing is needed. |
| > 10.0 | Overt Hypothyroidism (Underactive Thyroid) | Further testing and clinical evaluation is needed. Treatment with thyroid hormone replacement is necessary. |
*While the American Thyroid Association recommends that TSH levels be below 4.0 mIU/L, we recommend keeping levels below 2.5 mIU/L if you can do so naturally (diet, lifestyle, and supplementation).
Here at PrimeHealth, we prefer to administer a set of thyroid function tests that includes the TSH level test but also laboratory tests for:
- Free T4 (thyroxine)
- Free T3 (triiodothyronine)
- Total T4
- Total T3
- Reverse T3
- Anti-thyroglobulin and anti-TPO antibodies (Hashimoto’s thyroid antibodies)
- Thyroid-binding globulin (TBG levels)
We use these additional tests to help gain a picture of your overall thyroid function, as well as help to uncover the underlying reasons your thyroid function may be suboptimal. See this article for more information about full thyroid panel testing.
What Happens if My TSH Level Is High?
If your TSH level is high, it typically indicates that your thyroid gland is not producing enough thyroid hormones. Hashimoto’s thyroiditis, congenital hypothyroidism, pituitary disorders, primary hypothyroidism, and treatments for hyperthyroidism (like radioactive iodine therapy and anti-thyroid medications) can cause hypothyroidism.
Here’s what can happen and what it might mean for your health:
- Symptoms of Hypothyroidism: You might experience symptoms like fatigue, weight gain, dry skin, cold intolerance, constipation, muscle weakness, depression, and slowed heart rate.
- Metabolic Slowdown: Since thyroid hormones are crucial for metabolism, a deficiency can slow down metabolic processes. This can lead to weight gain and decreased energy levels.
- Increased Cholesterol Levels: Hypothyroidism can lead to dyslipidemia, a pattern of LDL, HDL, and triglycerides that makes us prone to heart disease.
- Heart and Circulatory Issues: Over time, untreated hypothyroidism can lead to a risk of heart disease and heart failure due to its impact on cholesterol levels and the heart muscle.
- Mental Health Impact: Hypothyroidism can affect your mental health, leading to depression or a slowdown in cognitive functions.
- Women’s Health Concerns: In women, high TSH levels can disrupt menstrual cycles, cause problems with fertility, and during pregnancy, can affect both the mother’s and the baby’s health.
- Muscle and Joint Pain: You may experience general muscle weakness and joint pain.
- Impact on Other Body Functions: Hypothyroidism can also affect other body functions, including digestion and the ability to maintain body temperature.
What to Do
It’s important to consult a healthcare provider when you notice unexpected symptoms like those above. At PrimeHealth, we’ll conduct further tests to confirm the diagnosis and begin working on a treatment plan.
Hypothyroidism and autoimmune diseases like Hashimoto’s thyroiditis are commonly treated with synthetic thyroid hormone replacement (like levothyroxine). We prefer to take a functional approach, incorporating diet, lifestyle changes, and supplementation into our treatment to address the root cause of your condition.
If you begin thyroid hormone replacement, your TSH levels must be monitored regularly to ensure the dosage is correct.
What Happens if My TSH Level Is Low?
A low TSH level usually points to hyperthyroidism. Having an overactive thyroid can be caused by Graves’ disease, thyroid nodules, and overmedication.
A less common cause for a low TSH would be due to pituitary dysfunction, also known as secondary hypothyroidism.
Here are the risks of hyperthyroidism and what it might mean if it goes unaddressed:
- Symptoms of Hyperthyroidism: Common symptoms include rapid heart rate, anxiety, tremors, weight loss despite normal or increased appetite, heat intolerance, increased sweating, and fatigue.
- Metabolic Acceleration: An overactive thyroid accelerates your body’s metabolism, leading to sudden weight loss and a rapid or irregular heartbeat.
- Heart Issues: A persistently low TSH and high thyroid hormone levels can lead to heart-related complications like atrial fibrillation (a type of irregular heartbeat) and an increased risk of heart disease.
- Bone Health Concerns: Over time, hyperthyroidism can cause bones to become weaker and more prone to fractures, a condition known as osteoporosis, especially in postmenopausal women.
- Eye Problems (Graves’ Ophthalmopathy): In conditions like Graves’ disease, one of the common causes of hyperthyroidism, eye problems can occur, such as bulging eyes, vision issues, and eye irritation.
- Menstrual Cycle Changes: Women may experience lighter and less frequent menstrual periods.
- Muscle Weakness: You might experience muscle weakness and tremors.
- Impact on Mood and Sleep: Hyperthyroidism can cause nervousness and anxiety and lead to sleep disturbances.
What to Do
Your provider will likely want to confirm the diagnosis with additional laboratory tests. Treatment for hyperthyroidism can include medication to reduce thyroid hormone production, radioactive iodine therapy, or, in some cases, surgery. The choice of treatment depends on the cause of hyperthyroidism, your age, and other health factors.
Since hyperthyroidism is usually caused by an autoimmune condition called Grave’s Disease, a functional medicine approach to treating it can be extremely beneficial and can even reverse it completely.
Lifestyle changes such as stress management, a balanced diet that focuses on whole foods, supplements, and trying an autoimmune Paleo diet can help control or even reverse thyroid problems.
Get Help Understanding Your TSH Levels
If you suspect you may have an undiagnosed thyroid condition and are looking for a more holistic approach to your health, reach out to a functional healthcare provider in your area.
Colorado residents: Our team is dedicated to finding the root cause of your concerns and empowering patients to take control of their health. Let us help you get back to living!
Sources
- Walsh, J. P. (2022). Thyroid function across the lifespan: do age-related changes matter?. Endocrinology and Metabolism, 37(2), 208-219.
- Li, J., Liu, A., Liu, H., Li, C., Wang, W., Han, C., … & Shan, Z. (2019). Maternal TSH levels at first trimester and subsequent spontaneous miscarriage: a nested case–control study. Endocrine Connections, 8(9), 1288-1293.
- McNeil, A. R., & Stanford, P. E. (2015). Reporting thyroid function tests in pregnancy. The Clinical Biochemist Reviews, 36(4), 109.
