Prolactin is a hormone that is best known for allowing pregnant and breastfeeding women to produce milk. It also plays a role in many other functions throughout the body in both males and females.
What is Prolactin?
Prolactin is a peptide hormone made by the pituitary gland and various other parts of the body. It is also referred to as the luteotropic hormone (luteotropin) and PRL. Prolactin is encoded by the PRL gene .
Primarily, prolactin is responsible for the stimulation of milk production in women (lactogenesis) .
When a woman is pregnant, prolactin levels increase by up to 10 – 20 times the normal amount. The levels return to normal within a few weeks after the mother stops breastfeeding.
Despite what its name suggests, prolactin does much more than only promote lactation. It is found in men as well and is influential in over 300 separate processes. It is recognized as a multipurpose hormone with one of the widest ranges of physiological actions of any hormone .
Prolactin is important for water/salt regulation, metabolism, reproductive behavior, the immune system, hormones, and the brain .
Functions of Prolactin
1) Helps Create Breast Milk
Milk production occurs after birth by allowing prolactin levels to remain elevated while progesterone and estrogen undergo an abrupt drop as they are rapidly cleared in 3-4 days after birth from the body. Estradiol acts at the hypothalamic level to increase prolactin secretion .
In the process of milk production, prolactin, along with cortisol and insulin, act together to stimulate genes that encode milk proteins.
Together, they stimulate the uptake of various amino acids and glucose, and the synthesis of the milk proteins (casein), fats, sugar (lactose), spermidine, and phospholipids, which are required for milk production. Non-pregnant levels of prolactin are sufficient to maintain milk production .
In breastfeeding mothers, prolactin is mainly secreted in response to stimulation of the nipples and breast by a suckling infant. The suckling by the baby blocks the secretion of hypothalamic dopamine (which normally inhibits prolactin). This results in a sharp rise in prolactin concentrations in the blood, followed by a prompt fall when feeding stops .
Biochemically, prolactin activates the Jak2/STAT5 pathway, which is responsible for milk production.
2) Plays a Role in Breast Development
Prolactin is merely a player in an orchestra of hormones and growth factors that support breast development.
Normal breast development requires prolactin, estrogen, progesterone, growth hormone, insulin, cortisol, thyroid and parathyroid hormone, IGF-1, and EGF. All of these together result in a functional gland.
Increased concentrations of prolactin in the blood during pregnancy cause enlargement of the mammary glands in order to prepare for milk production .
3) Makes You More Nurturing and Influences Sexual Desire
In humans, high prolactin levels are associated with nurturing and parenting behaviors, as well as psychosomatic reactions including false pregnancy.
Prolactin may have a role in paternal care as well (in fish and birds). In species where the male plays some role in the rearing of the offspring (rats), including humans, studies have found an association between prolactin and paternal care .
In women, prolactin can both increase or decrease sexual desire, and this depends on various factors. In men, prolactin suppresses sexual behavior in rats.
4) Helps Fetal Brain Development
Prolactin promotes neurogenesis in the mother and her fetus, immune tolerance of the fetus during pregnancy and contributes to the development of the fetal lungs .
5) Helps Fertility (sometimes)
Since prolactin increases progesterone, it helps to sustain pregnancies .
Thus, high prolactin concentrations during breastfeeding reduce fertility, protecting women from a premature pregnancy .
At lower levels, prolactin can contribute to male fertility in mice , but high prolactin causes infertility in males. It can also cause low testosterone, a lack of sexual desire, or erectile dysfunction .
Prolactin Affects Other Hormones
Elevated levels of prolactin decrease the levels of estrogen in women and testosterone in men. The effects of altered levels of prolactin on sex hormones are much more profound in women, substantially increasing or decreasing estrogen levels .
Normal levels of prolactin in males enhance testosterone secretion and the creation of sperm .
Prolactin decreases hepcidin, which can increase blood iron levels .
Normal Levels of Prolactin
The upper threshold of normal prolactin is about 25 µg/L for women and 20 µg/L for men. Prolactin levels below 3 µg/L in women and 5 µg/L in men are considered too low. Prolactin levels may be checked as part of a sex hormone workup since elevated prolactin secretion can suppress the secretion of other hormones like FSH, GnRH, and sex hormones (15).
Ideal levels of prolactin for men are probably between 5-10 µg/L.
Prolactin level blood tests are most accurate if conducted during the midmorning and not after stress, breast stimulation, physical examination, or other prolactin-increasing stimuli. In addition, elevated levels of prolactin should always be rechecked due to the variability of secretion and inaccurate test readings .
Prolactin levels rise to start one hour after a person falls asleep until peak amounts are reached between 5:00 and 7:00 AM. The lowest levels occur during the midmorning after waking .
Normal Prolactin Levels in the Blood:
|Nonpregnant women||4-23 nanograms per milliliter (ng/mL) or 4-23 micrograms per liter (mcg/L)|
|Men||3-15 ng/mL or 3-15 mcg/L|
|Pregnant women||34-386 ng/mL or 34-386 mcg/L|
|Children||3.2-20 ng/mL or 3.2-20 mcg/L|
High Levels of Prolactin
Higher levels of prolactin are found in pregnancy and breastfeeding .
High levels of prolactin in a woman may cause:
- Abnormal nipple discharge
- Infertility/Difficulty getting pregnant
- Low estrogen and progesterone levels 
- Difficulty getting a period
- Vision problems
High prolactin in males can cause :
- Low testosterone
- Low sexual desire
- Erectile dysfunction
A small benign tumor (microprolactinoma) is found in the pituitary of over one-third of women with high levels of prolactin.
Low Levels of Prolactin in Men
Low prolactin is associated with ovary dysfunction in women.
In men low prolactin is associated with:
- Low testosterone
- Erectile dysfunction
- Premature ejaculation
- Low sperm count
- Reduced sperm motility
- Decreased function of seminal vesicles
In one study on low prolactin in men, normal sperm function was restored when prolactin levels were raised back to their correct values.
In mice without prolactin receptors, the hair cycle is disrupted such that shedding occurred earlier and there was a reduced duration of the telogen phase .
What Increases Prolactin?
Prolactin levels are the highest during sleep, shortly after you wake up, and during times of physical or emotional stress.
In a study on female volunteers under hypnosis, prolactin surges resulted from rage or humiliating experiences, but not from the fantasy of nursing. Interestingly, compared to single males, fathers generally have higher prolactin concentrations (18).
The most consistent stimulus for prolactin secretion in males is stress .
Production of the prolactin-receptor in the brain increases with age, exposure to estrogens, elevation in prolactin levels, and by contact with babies.
Conditions with increased prolactin:
- Tumors of the pituitary gland (prolactinomas)
- Kidney disease
- Liver disease
- Antipsychotics (via blocking DRD2 receptors) .
- Some drugs and medications
Activities that increase prolactin:
Hormones that increase prolactin:
- TRH 
- Progesterone – increases prolactin synthesis in the endometrium and decreases it in the myometrium and breast glandular tissue
- Vitamin D/Calcitriol 
- Low DHEA
What Decreases Prolactin?
Low prolactin can be caused by :
Hormones that decrease prolactin:
Supplements that decrease prolactin:
The primary Prolactin Inhibiting Factor (PIF) is the neurotransmitter dopamine. When prolactin is produced, the secretion of dopamine increases as well, which then restricts prolactin production.
Treatment with dopamine or compounds that activate dopamine receptors suppresses prolactin secretion.
Studies have shown that increased levels of estrogen correlate to higher amounts of prolactin secretion. This is confirmed by the fact that women have higher levels of prolactin in their blood during stages of pregnancy and their reproductive cycle when estrogen levels are higher too.
Estrogen enhances the growth of prolactin-producing cells, stimulates prolactin production directly, and suppresses the production of dopamine.
Progesterone increases and decreases prolactin, depending on the area of the body.
Prolactin: The Bad
Many of the metabolic and immune functions of prolactin can be observed in males, but some of the effects of prolactin might not be high enough to be significant .
1) Is an Immune Stimulant
Prolactin is mostly an immune stimulant. The hormone plays a role in autoimmune diseases.
Immune responses (B cell, T cell) in organisms are enhanced by prolactin.
Treg cells help create tolerance and an anti-inflammatory environment.
Prolactin stimulates T effector cells (not good for autoimmune) and increases IFNy secretion, which encourages an inflammatory environment and Treg cell malfunction .
However, prolactin deficiency can cause immunodeficiency.
Interestingly, mice without the prolactin gene fail to show significant abnormalities in immune responses. As a result, prolactin has a modulatory role in several aspects of immune function but is not strictly required for these responses.
2) Can Cause Autoimmune Disease
- Autoimmune thyroid disease
- Alopecia 
- Systemic lupus erythematosus 
- Rheumatoid arthritis
- Psoriasis 
- Systemic sclerosis
- Polymyalgia rheumatica
- Sjogren’s syndrome – excess prolactin is diagnosed in nearly one-third of these patients
- Psoriatic arthritis – Drugs that lower prolactin help and improve joint and skin symptoms .
3) Can Cause Weight Gain and Hunger
Prolactin receptors are found in fat tissue, liver, pancreas and the brain .
Prolactin promotes appetite and contributes to the rapid increase in food intake during pregnancy and nursing .
Interestingly, gene studies have revealed that a common variant adjacent to the prolactin gene is associated with obesity .
4-5) Can Cause Anxiety and Depression
A byproduct of prolactin (vasoinhibins) causes depression and anxiety.
There is a correlation between prolactin and anxiety in men .
Prolactin levels in unipolar depressive patients are related to dissociative symptoms .
Prolactin may cause mood issues because of it regulates receptor potential thresholds, neuronal excitability and/or neurotransmission efficiency .
6) May Worsen Migraines and Cause Pain
Women who were given a drug to lower prolactin experienced improvement in their migraines .
7) Inhibits Blood Vessel Growth
Prolactin increases vasoinhibins, which are known for their inhibiting effects on blood vessel growth, vasopermeability, and vasodilation .
Disturbances of the prolactin/vasoinhibin axis are associated with the development of retinal diseases, cardiac diseases, and diseases occurring during pregnancy .
8) May Cause Cystic Fibrosis
Prolactin is one of the possible causes of cystic fibrosis.
9) May Increase Cancer Risk
Prolactin may increase breast and prostate tumors .
Prolactin: The Good
Now that we went through all the bad aspects of prolactin, it’s important to understand that there are also good elements.
1) Electrolyte Balance
Prolactin acts on the kidney to promote sodium, potassium, and water retention.
2) Is an Important Hormone During Sex
Prolactin provides the body with sexual gratification after sexual acts. The hormone counteracts the effect of dopamine, which is responsible for sexual arousal. This is thought to cause the sexual refractory period .
The amount of prolactin can be an indicator of the amount of sexual satisfaction and relaxation. Unusually high amounts are suspected to be responsible for impotence and loss of libido .
3) Increases Neurogenesis
In rats, prolactin can induce neurogenesis in the subventricular zone and the dentate gyrus .
Where Prolactin is Found in the Body
- Prolactin is found to be secreted from the uterus, placenta, immune cells, brain, breasts, prostate, skin, and fat tissue .
- Prolactin receptors are present in the breasts, ovaries, pituitary glands, heart, lung, thymus, spleen, liver, pancreas, kidney, adrenal gland, uterus, skeletal muscle, skin, and areas of the brain .
Irregular Prolactin Levels?
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