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What Is Thyroid Stimulating Hormone (TSH) And Which Blood Tests Check TSH Levels?

​What Is Thyroid Stimulating Hormone (TSH)?

Thyroid stimulating hormone (TSH) regulates the production of thyroid hormones. The thyroid gland is a small, butterfly-shaped gland located in the neck which produces thyroxine (T4) and triiodothyronine (T3). TSH is produced in the pituitary gland found just below the brain. The hormone is a major component of the feedback system responsible for the stabilisation of thyroid hormones in the blood. [1]

Which tests include this marker?

Why Take A TSH Blood Test?

A thyroid stimulating hormone test identifies hypo and hyperthyroidism. TSH controls the release of thyroid hormones into the blood. Ultimately, TSH tells us how well the thyroid gland is working. The test is used if an individual is experiencing symptoms of an overactive or an underactive thyroid.

You can test your TSH level along with other key thyroid hormones by purchasing a simple at-home finger prick test kit which is then analysed at an accredited lab. Forth offers a number of blood tests which include TSH such our thyroid function checkMale HormonesFemale FertilityMenopause Health and our Vitality package which includes analysis of over 30 key biomarkers for good health.

What Function Does TSH Have In The Body?

The main function of the thyroid stimulating hormone is to regulate thyroid function. TSH is produced by the pituitary gland and when the thyroid hormone concentrations fall below normal, the pituitary gland releases TSH. The release of TSH increases the release of T4 and T3 into the bloodstream. Usually, the serum hormone levels will return to normal and the production of TSH switches off, maintaining blood thyroid hormone concentrations at a constant rate within normal parameters.[2]

How Do Changes In TSH Affect Health And Wellbeing?

If there is too much TSH in the blood, then this can indicate an issue with the thyroid gland in that it is not producing enough thyroid hormone and could signify an underactive thyroid. An underactive thyroid can cause lethargy and fatigue as well as weight gain and increased sensitivity to the cold. Therefore, these effects can make the individual feel quite unwell and may affect their quality of life.

Too little TSH levels and the thyroid gland is likely to have be overactive. The reason for the low levels of TSH is because hyperthyroidism suppresses TSH. Individuals with an overactive thyroid experience weight loss, feel hot and depression or anxiety.[3]

If you are worried about your thyroid function or just want to check where you fall on the range, you can test your TSH level with a simple at-home blood test.

What Can Cause TSH To Change?

Hyperthyroidism causes excess thyroid hormones to be produced and is also known as an overactive thyroid. The most common cause of hyperthyroidism is an autoimmune disease where the immune system attacks its own thyroid cells.

Hypothyroidism occurs because of an underactive thyroid. In this case, the thyroid does not produce enough thyroid hormone. A variety of factors can cause hypothyroidism.

The most common cause of hypothyroidism is autoimmune thyroid disease where the body’s immune system attacks its own thyroid cells as if they were foreign. A common form is Hashimoto’s thyroiditis. The condition has a genetic susceptibility with both immune-related and thyroid-specific genes involved in the development of the disease.[4]

Other causes of hypothyroidism include radioactive iodine treatment and antithyroid drugs which are used to correct and treat an overactive thyroid. Some cough medicines also contain high amounts of iodine which can interfere with thyroid function. This is also true of some health foods like kelp, another food high in iodine. Iodine is essential to produce thyroid hormones.[5] 

What Are The Most Common Symptoms Of An Overactive or Underactive Thyroid?

The symptoms of an overactive thyroid are:

  • Changes in mood
  • Anxiety
  • Nervousness
  • Difficulty sleeping
  • Irregular or fast heartbeat
  • Weight loss
  • Trembling
  • Increased risk of cardiovascular risk
  • Swelling in the neck, goitre

The symptoms of an underactive thyroid, include:

  • Fatigue
  • Weight gain
  • Dry skin and hair
  • Depression
  • Muscle aches
  • Sensitivity to the cold

How To Keep TSH In The Healthy Range

Thyroid dysfunction is often caused by an autoimmune condition and although it may require medical intervention, lifestyle changes can help to restore its function. Changes to diet and lifestyle can help to control the symptoms of an over or underactive thyroid.

Although iodine is essential for the function of the thyroid gland, too much or too little can have negative effects. [6] Adults need 150 micrograms of iodine per day, most of which should be able to be obtained through eating a healthy, balanced diet. Individuals who are already taking thyroid medication like levothyroxine for an underactive thyroid, then you should not need to supplement your diet with iodine. [7]

Individuals with a thyroid condition are susceptible to vitamin B12 deficiency. It is particularly prevalent in hypothyroidism possibly because of their nutritional status. Plus, autoimmune thyroid disease is associated with autoimmune disorders such as pernicious anaemia which can lead to vitamin B12 malabsorption. [8] Therefore, an adequate intake of B vitamins is essential. Vegans and vegetarians are also susceptible to deficiency because vitamin B12 is found in animal products. Although some foods are fortified with the vitamin, susceptible groups may need supplementation. Good sources of vitamin B12 are:

  • Liver
  • Beef
  • Haddock
  • Tuna
  • Salmon
  • Trout
  • Eggs
  • Milk
  • Cheese
  • Fortified breakfast cereals [9]

Physical exercise has great effects on energy metabolism by increasing energy expenditure as well as increasing the body’s resting metabolic rate for hours following exercise. Some research has shown that exercise performed at 70£ of maximum heart rate increases the level of T3 and FT4. [10]

However, some studies contradict this and state exercise doesn’t have any major effect on circulating levels of thyroid hormones. Yet, exercise has other beneficial advantages for weight loss, psychological symptoms like depression and anxiety, all of which can affect individuals with a thyroid issue.

Tests that include this marker

Thyroid check

Test your level of TSH, T3 and T4, the three main hormones that indicate if your thyroid is functioning correctly.




Track & learn how to improve 16 of the most essential health markers with the Baseline blood work test which gives you an insight into your general health and overall wellbeing.

£59 per test

Advanced Thyroid Check

An advanced thyroid check which measures key thyroid hormones TSH, FT4 and FT3 together with thyroid antibodies.


Male Hormones

A comprehensive test of key male hormones which can affect libido, muscle strength, energy and much more.


Female Hormones

Our female hormone blood test checks levels of a range of key hormones that affect fertility, mood, energy levels and even your weight. Understand your hormone health quickly, easily and affordably.


Baseline Plus


Measure & track 20 key biomarkers including those essential for a strong immune system, energy levels, strong bones and good sleep.

£79 per test

Menopause Health

For women in various stages of the menopause who want to check hormone levels as well as the impact changes may be having on their overall wellbeing.



With over 45 biomarkers, this health check empowers you to gain a deep understanding about your inside health.



Our most advanced health check which analyses over 50 biomarkers. For those who want a deep understanding of their health.



[1] Lab Tests Online UK. (2015). TSH. Available at:

[2] Szkudlinski, M, W et al. (2002). Thyroid-Stimulating Hormone and Thyroid-Stimulating Hormone Receptor Structure-Function Relationships. Physiol. Rev(82), pp 473-502.

[3] You and Your Hormones. (2018). Thyroid Stimulating Hormone. Available at:

[4] Ajjan, R, A and Weetman, A, P. (2015). The Pathogenesis of Hashimoto’s Thyroiditis: Further Developments in Our Understanding. Horm Metab Res: 47, pp 702-710.

[5] British Thyroid Function. (2018). Hypothyroidism. Available at:

[6] Chung, H, R. (2014). Iodine and Thyroid Function. Ann Pediatr Endocrinol Metab: 19, pp 8-12

[7] British Thyroid Foundation. (2018). Thyroid and Diet Factsheet. Available at:

[8] Collins, A, B and Pawlak, R. (2015). Prevalence of Vitamin-B12 Deficiency Among Patients with Thyroid Dysfunction. Asia Pac J Clin Nutr: 25(2), pp 221-226.

[9] National Institutes of Health: Office of Dietary Supplements. (2018). Vitamin B12. Available at:

[10] Ciloglu, F., Peker, I., Pehlivan, A., Karacebey, K., Ilhan, N., Saygin, O and Ozmerdivenli, R. (2005). Exercise Intensity and its Effects on Thyroid Hormones. Neuro Endocrinol Lett: 26(6), pp 830-834.

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