Thyrotrophin-releasing hormone (TRH)

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What is TRH?
Where is TRH produced?
Function of TRH
How TRH is regulated
Causes of high TRH
Causes of low TRH
Testing TRH
TRH in traditional Chinese medicine
Acupuncture and TRH
Chinese herbal medicine and TRH
Diet and lifestyle
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1. What is TRH?

Thyrotrophin-releasing hormone (TRH) is a small peptide hormone produced by the hypothalamus. Its primary role is to stimulate the anterior pituitary gland to release thyroid stimulating hormone (TSH), which in turn signals the thyroid gland to produce the active thyroid hormones thyroxine (T4) and triiodothyronine (T3). TRH is therefore the most upstream signal in the hypothalamic-pituitary-thyroid (HPT) axis.

Although thyroid hormones are not commonly thought of as fertility hormones, they have a profound effect on female and male reproduction. Even subtle thyroid imbalances can disturb the menstrual cycle, suppress ovulation, thin the uterus lining, increase the risk of miscarriage and impair sperm quality. Through its control of TSH, TRH therefore plays a meaningful role in fertility.

Reference ranges vary from country to country and between laboratories. TRH itself is not routinely tested in clinical practice; instead, the integrity of the HPT axis is assessed by measuring TSH and the thyroid hormones T4 and T3.

2. Where is TRH produced?

TRH is produced by neurones in the paraventricular nucleus of the hypothalamus. Like GnRH, it is released into the small hypophyseal portal blood vessels that connect the hypothalamus to the anterior pituitary, allowing it to act on the pituitary in much higher concentrations than would be possible through the general circulation. Small amounts of TRH are also produced in other tissues including the spinal cord, gastrointestinal tract and pancreas, where it has a range of less well-understood functions.

3. Function of TRH

TRH binds to TRH receptors on cells of the anterior pituitary gland and stimulates two main actions:

Release of thyroid stimulating hormone (TSH) — TSH then travels to the thyroid gland and stimulates it to produce T4 and T3. Adequate thyroid hormone levels are essential for normal ovulation, a healthy uterine lining and normal sperm production.
Release of prolactin — TRH is one of the stimuli for prolactin release. This is why women with primary hypothyroidism (where the thyroid is underactive and the hypothalamus produces more TRH to compensate) often have elevated prolactin levels, which can in turn suppress ovulation and cause infertility.

4. How TRH is regulated

TRH release is regulated by a number of feedback signals:

Negative feedback from T4 and T3 — when thyroid hormones rise, they suppress TRH and TSH. When they fall, TRH and TSH rise.
Cold exposure — exposure to cold temperatures stimulates TRH release, increasing thyroid hormone production and metabolism.
Stress — acute stress can stimulate TRH, but chronic stress and elevated cortisol generally suppress the HPT axis.
Leptin — adequate leptin signalling from adipose tissue is required for normal TRH release. Low body fat and undereating suppress TRH and reduce thyroid output.

5. Causes of high TRH

TRH rises in:

Primary hypothyroidism — when the thyroid gland fails, both TRH and TSH rise as the hypothalamus and pituitary try to compensate. This is the most common cause of elevated TRH and is often associated with elevated prolactin and infertility.
Hashimoto's thyroiditis — autoimmune destruction of the thyroid gland causes progressive hypothyroidism with high TRH and TSH.
Iodine deficiency — without iodine the thyroid cannot produce T4 and T3, leading to elevated TRH and TSH.

6. Causes of low TRH

TRH may be low in:

Hyperthyroidism — high circulating thyroid hormones suppress TRH and TSH.
Hypothalamic dysfunction — caused by chronic stress, severe undereating or pituitary disease.
Severe illness — TRH and TSH are often suppressed in critical illness as part of the so-called "low T3 syndrome".

7. Testing TRH

TRH itself is not measured in routine clinical practice because of its short half-life and release into the small hypophyseal portal system. Instead, the function of the hypothalamic-pituitary-thyroid axis is assessed by measuring TSH, free T4 and free T3. A TRH stimulation test is occasionally used in specialist endocrinology, but is rarely required in general fertility practice.

Reference ranges vary from country to country and between laboratories. For TSH, most UK reference ranges are 0.4–4.0 mU/L, but for optimal fertility, TSH should be below 2.5 mU/L. Always interpret your test results against the laboratory's own reference range and discuss them with your doctor or fertility specialist.

8. TRH in traditional Chinese medicine

In traditional Chinese medicine, the function of the thyroid axis is closely related to the Kidney Yang — the warming, activating, metabolism-driving aspect of Kidney function. When Kidney Yang is deficient, the body becomes cold, the metabolism slows, the menstrual cycle lengthens and ovulation becomes weak — a pattern that closely matches western hypothyroidism. Where the underlying problem lies in the hypothalamus or pituitary, the Kidney–Liver–Heart axis is involved, with the Liver responsible for the smooth release of TRH-like signals.

9. Acupuncture and TRH

Acupuncture has been shown in research to regulate the hypothalamic-pituitary-thyroid axis and to normalise both TSH and thyroid hormones in women with subclinical and overt hypothyroidism. Because TRH sits at the top of this axis, acupuncture can be considered to act indirectly on TRH function. I use acupuncture in my clinic to support women with thyroid-related fertility problems, in conjunction with medical treatment where appropriate.

10. Chinese herbal medicine and TRH

Chinese herbal formulae that warm Kidney Yang — such as You Gui Wan, Jin Gui Shen Qi Wan and Er Xian Tang — are commonly used to support patients with underactive thyroid function. Where the Liver Qi is also stagnant from chronic stress, Xiao Yao San is added or used as the primary formula. Treatment is always individualised after a full TCM assessment.

11. Diet and lifestyle

To support a healthy hypothalamic-pituitary-thyroid axis:

Ensure adequate iodine intake — fish, seaweed, eggs and unrefined sea salt are good sources. Vegetarians and vegans are at higher risk of iodine deficiency.
Eat selenium-rich foods such as Brazil nuts, fish, poultry and whole grains. Selenium is essential for the conversion of T4 into the active T3.
Avoid excessive raw cruciferous vegetables (kale, cabbage, broccoli) if you have an underactive thyroid — light cooking deactivates their goitrogenic compounds.
Reduce psychological stress through mindfulness, meditation, yoga or counselling.
Sleep before 10 p.m. and aim for seven to eight hours per night.
Keep the body warm and avoid prolonged exposure to cold.