Prolactin

For example, it helps regulate the immune system, develop blood vessels, and manage behavior and mood. Prolactin also plays a role in controlling metabolism. 

Prolactin, often referred to as the "milk hormone," plays a crucial role in various physiological processes beyond lactation. This hormone, produced by the pituitary gland, is most famous for stimulating milk production in breastfeeding parents.  

Prolactin has many other functions, as it is involved in over 300 different processes in various tissues throughout the body.  Prolactin influences reproductive health, metabolism, and immune function. 

Disruptions in prolactin levels can lead to various health concerns, including fertility issues, menstrual irregularities, and sexual dysfunction. 

Understanding the functions of prolactin, as well as factors influencing its levels, is essential for maintaining overall health and addressing potential underlying conditions. In this article, we delve into the multifaceted aspects of prolactin, exploring its functions, testing methods, associated health implications, and strategies for managing its levels.

What is Prolactin?

Prolactin is a peptide hormone primarily known for its role in lactation and milk production in mammals. Produced primarily by the lactotroph cells of the anterior pituitary gland, prolactin secretion is regulated by the hypothalamus through the release of various PRFs, or prolactin-releasing factors, as well as various prolactin-inhibiting factors (PIF).  Dopamine is one well-known PIF, and the stress hormone adrenaline may be another.  [4.] 

However, not only the pituitary gland but also various other tissues such as the central nervous system, the immune system, the uterus, and the mammary glands have the capacity to produce prolactin. Factors like nipple stimulation, exposure to light, olfaction, and stress can all trigger the synthesis of prolactin in these tissues.  [1.]

Beyond its function in lactation, prolactin has diverse physiological effects, including reproductive regulation, immune modulation, and metabolic regulation.  [5.]

Functions of Prolactin: What Does Prolactin Do?

Prolactin is a crucial hormone in reproduction and lactation, exerting various effects on mammary gland development, milk synthesis, and maintenance of milk secretion. [5.]  Its role in lactogenesis involves stimulating the synthesis of milk proteins, promoting glucose uptake, and enhancing milk fat production. 

Prolactin also influences luteal function, acting either as a luteotrophic hormone to maintain the corpus luteum's integrity during pregnancy or as a luteolytic agent to induce programmed cell death in the absence of pregnancy and implantation. 

Prolactin also plays a role in reproductive behavior by impacting female receptivity, parental care, and even paternal behavior in certain mammals. 

Prolactin receptors are located within the hypothalamus, suggesting a role in modulating neuronal activity and gene expression, although specific signal transduction pathways in the central nervous system are still under investigation.

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Prolactin also acts as a mediator within the immunoneuroendocrine network, influencing communication between the nervous, endocrine, and immune systems. [5.]  It plays a pivotal role in regulating both humoral and cellular immune responses, impacting physiological functions as well as pathological conditions like autoimmune diseases. 

Early studies revealed that prolactin enhances thymic function and is crucial for maintaining immune homeostasis. Prolactin stimulates mitogenesis in T lymphocytes and the Nb2 lymphoma cell line, and its effects on lymphocytes are mediated through interactions with interleukin-2 (IL-2). 

Moreover, prolactin's role extends beyond the immune system; it affects solute and water transport across cell membranes and exhibits both angiogenic and antiangiogenic activities, suggesting diverse physiological functions beyond lactation regulation.

Understanding Prolactin Levels

What Happens When Prolactin Levels are High?

Elevated levels of prolactin, known as hyperprolactinemia, can have various effects on the body. 

In women, high prolactin levels can disrupt the normal menstrual cycle and lead to irregular periods or even cessation of menstruation (amenorrhea). It can also cause galactorrhea, a condition characterized by the spontaneous production of breast milk outside of pregnancy or breastfeeding. 

Additionally, high prolactin levels might interfere with ovulation, leading to infertility or difficulty conceiving.  Prolactin is known to stimulate androgen secretion from the adrenal glands.  [8.]

In men, elevated prolactin levels can result in decreased libido, erectile dysfunction, and in severe cases, infertility. 

Both genders may also experience symptoms such as headaches, visual disturbances, and in rare instances, enlargement of the pituitary gland due to a prolactinoma, a pituitary prolactin-producing tumor.  This can cause further hormonal imbalances and neurological symptoms.

Causes of High Prolactin Levels

Several factors can contribute to elevated prolactin levels, including physiological, pathological, and iatrogenic causes. 

Physiological factors such as pregnancy, breastfeeding, and nipple stimulation can temporarily increase prolactin levels. However, persistent hyperprolactinemia may be indicative of underlying health conditions such as pituitary tumors (prolactinomas), which directly stimulate excessive prolactin production. 

Other causes include hypothyroidism and chronic kidney disease, which can disrupt the regulation of prolactin secretion.  [2.]  Some experts recognize liver cirrhosis, particularly with encephalopathy, as an additional cause of increased prolactin levels, although that is contested by others.  [12., 13.]

Estrogen can also stimulate prolactin release, particularly in pregnancy.  [1.]

Certain medications like antipsychotics, antidepressants, and antihypertensive drugs can also elevate prolactin levels as a side effect. [11.]  Additionally, stress, intense physical activity, and sleep disturbances may contribute to transient increases in prolactin secretion. [3., 7., 10.] 

Identifying and addressing the underlying cause of high prolactin levels is crucial for appropriate management and treatment.

Testing for Prolactin

What is a Prolactin Test?

A prolactin test measures the level of prolactin, a hormone produced by the pituitary gland, in the blood. This test is typically ordered to investigate conditions related to the reproductive system, such as infertility, irregular menstrual periods, or abnormal milk production (galactorrhea). 

It may also be requested if a healthcare provider suspects a pituitary disorder, such as a prolactinoma, which is a benign tumor of the pituitary gland that can cause elevated prolactin levels.

A morning sample is typically recommended, and fasting may or may not be recommended by the individual’s healthcare provider.  

Interpreting a Prolactin Test  [1.]

Common reference ranges for serum prolactin levels are:

• Males: 2 to 18 ng/ml
• Females:  2 to 30 ng/ml
• Females during the third trimester of pregnancy: 10 to 210 ng/ml. 

In cases of prolactinomas, the serum prolactin level is often greater than 200 ng/mL.

In cases of elevated prolactin, a serum TSH, thyroid hormones, assessment of other hormones including estrogen, androgens, and human chorionic gonadotropin, as well as a cranial MRI should be considered.

Clinical Significance of Prolactin Testing

Prolactin testing holds significant clinical significance in diagnosing and monitoring various medical conditions. High levels of prolactin can indicate several underlying issues including pituitary tumors, hypothyroidism, kidney disease, or certain medications like antipsychotics.  Recognizing elevated prolactin levels is important to promote ovulation and fertility in women.   

Conversely, low levels of prolactin may be associated with pituitary dysfunction or inadequate glandular function. 

By assessing prolactin levels, healthcare providers can better understand and manage reproductive health issues, guide treatment decisions, and monitor the effectiveness of therapies aimed at correcting hormonal imbalances. Additionally, regular prolactin testing may be necessary to track changes over time and adjust treatment plans accordingly.

Managing High Prolactin Levels

How to Lower Prolactin Levels

Lowering prolactin levels often depends on addressing the underlying cause. In cases where high prolactin levels are due to medications, discontinuing or switching medications under medical supervision may help. 

Treatment options for prolactinomas (benign tumors of the pituitary gland) may include medications like dopamine agonists such as bromocriptine or cabergoline, which work by reducing prolactin production. Surgery or radiation therapy may be considered in cases where medications are ineffective or not well-tolerated. 

The Alternate Healthy Eating Index, along with reducing alcohol intake, were shown to reduce circulating estrogen levels in premenopausal women, which may be one strategy for reducing prolactin levels as well.  [9.]

Lifestyle modifications such as reducing stress levels and ensuring adequate sleep, may also support overall hormonal balance and contribute to lowering prolactin levels.  [3.]

Vitamin B6 has been shown to reduce circulating levels of prolactin, because of its effects in increasing dopamine.  [14.]

Lowering Prolactin Levels in Men

Lowering prolactin levels in men often involves similar approaches to those used in women, with the primary focus on addressing the underlying cause.

 If high prolactin levels are due to medication side effects, a healthcare provider may adjust the medication regimen or explore alternative treatment options. 

In cases where prolactinomas are present, dopamine agonist medications like bromocriptine or cabergoline may be prescribed to suppress prolactin production. These medications can help restore hormonal balance and alleviate symptoms associated with elevated prolactin levels. 

Adhering to a healthy lifestyle including following a healthy diet, reducing stress and ensuring adequate sleep, may also help to regulate prolactin levels in men.  Additionally, vitamin B6 supplementation may be considered as an adjunctive therapy.

Close monitoring by a healthcare provider is essential to assess treatment response and adjust therapy as needed to achieve optimal outcomes.

How to Increase Prolactin

Increasing prolactin levels can be achieved through various means such as nipple stimulation, stress reduction techniques, and when appropriate, certain medications like antipsychotics or antidepressants, which can directly stimulate prolactin secretion from the pituitary gland. 

Additionally, factors like high-protein meals, physical exercise, and sexual activity have been associated with transient increases in prolactin levels. However, it's important to note that artificially increasing prolactin levels should be done under medical supervision, as excessively high levels can lead to adverse effects and may indicate underlying health conditions.

For breastfeeding women seeking to naturally increase prolactin levels to support milk production, techniques like frequent and effective nursing or pumping sessions, ensuring proper hydration and nutrition, and practicing relaxation methods can be beneficial. Additionally, maintaining skin-to-skin contact with the baby and minimizing stress can help stimulate prolactin release. 

In some cases domperidone is used to support prolactin levels and stimulate breast milk production.  [6.]

It's important for breastfeeding mothers to prioritize their own well-being, as factors like fatigue, stress, and inadequate nutrition can negatively impact milk production. 

Consulting with a lactation consultant or healthcare provider can provide personalized guidance and support in optimizing prolactin levels for successful breastfeeding.

Prolactin and Fertility

Fertility Implications of High Prolactin Levels

High prolactin levels can have significant implications for fertility, as elevated levels of this hormone can disrupt the delicate hormonal balance necessary for ovulation and reproductive function. 

In women, high prolactin levels may lead to irregular menstrual cycles, anovulation, and difficulty conceiving. In some cases it can cause amenorrhea, the absence of menstruation altogether. Additionally, elevated prolactin levels can interfere with the production of other reproductive hormones like estrogen and progesterone, further impacting fertility. 

Many of the negative impacts of elevated prolactin on fertility in women are related to prolactin’s overstimulation of androgens, which causes hormone imbalance and PCOS.  

Men with high prolactin levels may experience decreased sperm production and quality, leading to infertility.  [1.]

Addressing and managing high prolactin levels through medication, lifestyle changes, and medical interventions may be necessary to improve fertility outcomes in affected individuals.

How to Lower Prolactin Levels to Enhance Fertility

Lowering prolactin levels to enhance fertility involves identifying and addressing underlying causes such as medication side effects, stress management, and treating any related medical conditions like hypothyroidism or polycystic ovary syndrome (PCOS).  

Medications like dopamine agonists may be prescribed to inhibit prolactin production and restore normal hormone balance. 

Lifestyle modifications such as regular exercise, maintaining a healthy weight, and ensuring adequate sleep can also contribute to lowering prolactin levels and improving fertility outcomes.  Diet and lifestyle modifications are especially important in the setting of elevated prolactin levels in PCOS or hyperandrogenism.  

Consulting with a healthcare provider or fertility specialist is essential for developing a tailored treatment plan based on individual needs and circumstances.

Tests for Prolactin Levels

Click here to explore tests for prolactin levels and associated tests.