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Thyroid Stimulating Hormone (TSH)

TSH is important for the normal functioning of the thyroid gland, find out what it is and what causes fluctuations in its levels.

Author: Leanne Edermaniger

May 20, 2024

Reviewed by: Dr Thom Phillips

In this article:

What is Thyroid Stimulating Hormone?

Thyroid stimulating hormone or TSH, is produced in the pituitary gland and regulates the production of thyroid hormones, thyroxine (T4) and triiodothyronine (T3).

The thyroid, a small butterfly-shaped gland in the neck responsible for the body’s metabolic rate, produces T3 and T4. If too much of these hormones are released it can cause your cells to work faster than they need to. If they are too low, the cells will work too slowly[1].

What function does TSH have in the body?

The pituitary gland produces TSH. It stimulates thyroid follicular cells to release the hormones T3 and T4.

High or low levels of TSH may indicate a thyroid disorder, such as an underactive (hypothyroidism) or overactive (hyperthyroidism) thyroid. These conditions affect the metabolic rate of your cells which can cause a wide range of symptoms.

Hypothyroidism, for example, can slow down your metabolism, cognition, and bowel movements, and lower your energy levels, impacting your quality of life. An overactive thyroid increases your metabolism which can also have a detrimental effect on your daily life. Both disorders also have a mental impact and cause emotional or psychological symptoms, such as anxiety, depression, or mood changes.

What is a Normal TSH Level?

A healthy TSH range is between 0.27 and 4.2 milliunits per litre mU/l[4], although this can vary depending on the testing laboratory.

Our data shows that the average TSH level in Forth customers is 2.4 mU/l:

  • 2.4 mU/l for men
  • 2.3 mU/l for women

The average TSH levels according to age are:

Age TSH (mU/l)
18 – 29 2.2
30 – 39 2.3
40 – 49 2.3
50 – 59 2.4
60+ 2.5

How To Check Your TSH Levels

The most accurate way to check your TSH levels is with a blood test.

You can check your TSH levels at home with our Advanced Thyroid Function Blood Test which measures 5 important biomarkers for thyroid health:

When you order a thyroid test kit from us, we will send everything you need to return a blood sample to our partner lab. Once your sample has been received, you’ll get your results within 2 working days.

A thyroid test which includes TSH can give you a good insight into your thyroid function. For most people, it is the most useful thyroid function test, and most do not require any other biochemical thyroid tests[5]. It can be used if you are experiencing any of the symptoms of an under- or overactive thyroid. However, measuring your TSH levels won’t tell you what’s causing a thyroid problem, just that you might have one.

What Causes High TSH Levels?

If there is an issue with your thyroid gland directly and there is no underlying cause, this is commonly referred to as primary thyroid disease.

Primary Thyroid Disease

Generally, high TSH levels are associated with an underactive thyroid or hypothyroidism. When the thyroid doesn’t produce enough T3 or T4, the negative feedback inhibition is lost, causing the pituitary gland to increase TSH production[6].

Hypothyroidism is diagnosed when TSH levels are high but T4 is usually within the normal reference range[7].

If you have primary hyperthyroidism or an overactive thyroid, then the gland produces large amounts of T3 and T4 which suppresses the production of TSH. So, TSH levels are likely to be low.

Primary hyperthyroidism can be diagnosed if TSH levels are below the normal range and T3 and/or T4 levels are high[8].

The most common causes of primary thyroid disease are autoimmune conditions:

  • Graves’ disease: The most common cause of hyperthyroidism.
  • Hashimoto’s thyroiditis is the most common cause of an underactive thyroid.

Secondary Thyroid Disease

Secondary thyroid disease is rare and caused by an issue with the pituitary gland or hypothalamus in the brain. Compared to primary thyroid disease, secondary types can cause different TSH levels.

For example, secondary hypothyroidism causes low or normal TSH levels but T4 is below normal. Secondary hyperthyroidism causes an increased production of TSH which results in high T3 and/or T4 levels.

Symptoms of Hyperthyroidism and Hypothyroidism

Metabolic rate slows down causing cells and organs to work slower than normal.
Speeds up your metabolism and causes cells and organs to work faster than they should.
Weight gain Anxiety or irritability
Tiredness  Weight loss 
Depression  Mood swings
Aching joints and muscles Sleep issues
Sensitivity to cold temperatures Feeling tired all the time
Dry hair and skin  Muscle weakness
Constipation  Thirst 
Carpal tunnel syndrome Sensitivity to heat
Slow movements/thoughts[2] Low libido[3]

Managing Your TSH Levels

Understanding what’s causing abnormal TSH levels is important because if you have an underactive thyroid, then you may require medication to correct your thyroid hormone levels.

However, there are some lifestyle factors which can maintain normal TSH levels

  • Diet: Although there are no specific foods to eat or avoid to cure thyroid disease, it is important to eat a healthy, balanced diet to make sure your body is getting all the nutrients it needs to function properly. You may need to be aware of your iodine intake because too little or too much can affect thyroid hormone production[9].
  • Exercise: Some research shows that aerobic exercise can lower the circulating levels of TSH to help maintain thyroid homeostasis[10]. Further research shows that exercise has a moderate effect on TSH levels in people with hypothyroidism and that it is a safe management intervention[11].

Following a healthy lifestyle is important to support the proper production of thyroid hormones and keep your metabolic health balanced. However, if your TSH levels are abnormally high or low, it is recommended to seek advice to rule out any underlying conditions. You may also require medication to help bring your levels back within a normal range.

Written by Leanne Edermaniger

Based in the UK, Leanne specialises in writing about health, medicine, nutrition, and fitness.

She has over 5 years of experience in writing about health and lifestyle and has a BSc (hons) Biomedical Science and an MSc Science, Communication and Society.

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Article references

  1. Altaye, K.Z. et al. (2019) ‘Effects of aerobic exercise on thyroid hormonal change responses among adolescents with intellectual disabilities’, BMJ Open Sport & Exercise Medicine, 5(1). doi:10.1136/bmjsem-2019-000524.

  2. ‘Effects of physical activity on thyroid stimulating hormone levels in obese metabolic syndrome patients: A meta-analysis’ (2023) Journal of the College of Physicians and Surgeons Pakistan, 33(11), pp. 1293–1298. doi:10.29271/jcpsp.2023.11.1293.

This article was written by Leanne Edermaniger

This information has been medically reviewed by Dr Thom Phillips

Thom works in NHS general practice and has a decade of experience working in both male and female elite sport. He has a background in exercise physiology and has published research into fatigue biomarkers.

Dr Thom Phillips

Dr Thom Phillips

Head of Clinical Services