Prolactin 101: Everything you need to know about prolactin-image

Prolactin 101: Everything you need to know about prolactin

Prolactin is perhaps best known as the ‘milk hormone’ because of its vital role in breast growth and breast milk (lactation) production. But prolactin actually has a myriad of functions within the body, playing a vital role in overall health for those both assigned-female and male-at-birth. 

In this article, we’ll dive into exactly what prolactin is, what its functions are in the body, discuss imbalances in its levels and the importance of testing prolactin levels for reproductive and overall health.

What is prolactin?

Prolactin is a hormone that encourages breast growth and milk production during and after pregnancy, as well as maintaining our metabolism, regulating our stress response, maintaining a functioning immune system and in the development of our reproductive organs. 

Similarly to follicle-stimulating hormone (FSH) and luteinizing hormone (LH) it is secreted by the anterior pituitary gland, located at the base of the brain. From there, it’s released into the bloodstream where it travels around the body to carry out its functions. 

Prolactin interacts with FSH and LH, and other cycle hormones, in a complex negative feedback loop. After ovulation prolactin production increases to prepare the body for a potential pregnancy.

Prolactin’s role in breastfeeding

In pregnant women, prolactin stimulates milk production in the mammary glands of the breasts—allowing for the secretion of breast milk. After birth, there is a postnatal rise in prolactin, which gets things started—but this isn’t enough to maintain breast milk development.

When a baby suckles, prolactin levels in the blood increase in response, which stimulates the production of more milk. Prolactin levels spike around 30 minutes since the start of the feed, so this positive feedback effect is important for ensuring there is enough milk for the next feed. 

This can also be stimulated by breast pumping, if you choose not to, or are unable to breastfeed.

Prolactin levels

Just like all of our hormones, from time to time, our prolactin levels can get off balance. This can cause a whole range of different symptoms and effects throughout the body, including affecting our thyroid hormones, stress hormones, menstrual cycles and ovulation.

What are normal prolactin levels?

Reference ranges for what is a normal prolactin level will be specific to the lab that is testing your sample. 

Higher prolactin levels are usually present in those assigned-female-at-birth than those assigned-male-at-birth. In general, prolactin levels are expected to be less than 25 μg/L in those assigned-female-at-birth, who are not pregnant or breastfeeding.

High prolactin levels

If you’re not pregnant or haven’t just given birth but experiencing abnormally high prolactin levels, this is known as hyperprolactinemia. 

Symptoms of high prolactin levels (hyperprolactinemia)

Too much prolactin can stop our brains from producing FSH and LH—two key hormones involved in regulating our menstrual cycles and bringing about ovulation. 

If FSH and LH are affected, ovulation can stop leading to the loss of periods, which is called amenorrhoea. No ovulation means no chance of a pregnancy, and therefore big issues for our fertility.

Disruption to our menstrual cycle can also cause knock-on effects on our oestrogen levels, causing oestrogen deficiency.

Some of the most common symptoms of high prolactin levels to look out for are milky white discharge from the nipples when not breastfeeding (galactorrhea), disturbances to the menstrual cycle, visual disturbances, headaches and symptoms of oestrogen deficiency.

High prolactin levels can be caused by a variety of reasons, including imbalances in our thyroid and stress hormones. Additionally, a growth or tumour present in our pituitary glands, called a prolactinoma, can also cause persistent or increasing prolactin levels.

Symptoms of high prolactin levels can include:

  • Visual disturbances, dizziness and or/headaches
  • Milky white nipple discharge (galactorrhea)
  • Menstrual cycle disturbances
  • Oestrogen deficiency symptoms
  • Persistent vomiting

Note: If you are experiencing any form of nipple discharge when not breastfeeding, get this checked by a physician or GP as it can be a symptom of breast cancer. 

Symptoms of high prolactin levels after menopause

Although high prolactin levels are not common in those postmenopausal, it can occur. Excess prolactin after menopause often causes hyperthyroidism, when the body doesn’t make enough thyroid hormone. 

Symptoms can include:

  • Fatigue
  • Weight gain
  • Muscle pains
  • Constipation 

How to lower prolactin levels

If you’re wondering how to reduce prolactin levels, this is very much dependent on the cause of your excess prolactin levels. 

Your doctor may prescribe you medications like bromocriptine or cabergoline to lower your prolactin secretion. Surgery may also be recommended as the best treatment option for you. 

Persistently high prolactin that has been caused by chronic stress, over-exercising or poor sleep may be lowered by lifestyle modifications.

Low prolactin levels

On the flip side, low prolactin levels, called hyperprolactinemia, is rare—and outside of pregnancy, baseline or ‘normal’ prolactin levels are usually low.

Sometimes there aren’t any obvious symptoms of low prolactin levels, other than not being able to produce or release much breast milk after giving birth.

Breastfeeding can increase our prolactin levels naturally—as the more we stimulate the nipples, more prolactin is produced. 

Most people with low prolactin levels don’t have any specific medical issues, although there is preliminary evidence that suggests they might have reduced immune response to some infections and it could indicate that the pituitary gland isn’t functioning properly.

Why should we test our prolactin levels?

Like all of our reproductive hormones, it’s good to check in with prolactin regularly, especially if we’re trying to conceive or having any problems with our menstrual cycles or experiencing hormonal symptoms. 

Testing our prolactin levels with a prolactin blood test can help us to determine if there are any hormonal issues affecting our fertility or menstrual cycle, or investigate any symptoms of prolactinoma.

With a Hertility Hormone and Fertility test, we can test your prolactin levels alongside your Anti müllerian hormone (AMH), thyroid hormones and cycling hormones (FSH, LH and oestrogen) to help you gain a full insight into your hormonal health and fertility.
If you’ve already done a test and received an abnormal prolactin result, you can book an appointment with one of our Private Gynaecologists specialising in hormone and fertility concerns to discuss your results and get a personalised care plan. Appointments are available daily, with no GP referral required.

Prolactin FAQs

Can I get an FSH, LH, Prolactin test all in one?

Luckily, you’re in exactly the right place. With our Hormone and Fertility test we will test you for up to 10 reproductive hormones, including your FSH, LH, prolactin and more. 

Do prolactin levels change with age?

Unlike hormones like Anti Müllerian Hormone (AMH) and oestrogen, our prolactin levels should stay relatively consistent post puberty until menopause, with the exception of when we’re pregnant or breastfeeding. After menopause, prolactin levels tend to be slightly lower. Most hormone tests don’t take into account a normal prolactin level by age, and instead have premenopausal and postmenopausal reference ranges. 

Does prolactin increase breast size?

Yes, increased prolactin levels cause the breasts to grow, which is why when we’re pregnant our breasts usually grow. If we’re experiencing high prolactin levels when we’re not pregnant, this can also cause breast swelling and tenderness.

Is high prolactin a sign of cancer?

In some cases, high prolactin levels can be associated with certain types of tumours—specifically benign tumours called prolactinomas. These are non-cancerous growths that develop in the pituitary gland in the brain where prolactin is produced, and are usually the result of excessive production of prolactin.

Key takeaways

  • Prolactin is an important hormone for the female reproductive system as well as for overall health
  • Prolactin has a well-established role within breast growth and breast milk production during and after pregnancy
  • Prolactin imbalances can interfere with our menstrual cycles and ovulation, impacting our fertility and chances of conceiving
  • Testing our prolactin regularly with a hormone and fertility test can help us get to the bottom of menstrual cycle irregularities or fertility issues

Resources

Zoya Ali BSc, MSc

Zoya Ali BSc, MSc

Zoya is a scientific researcher with a Bachelor's degree in Biotechnology and a Masters in Prenatal Genetics & Foetal Medicine from University College London. Her research interests are reproductive genetics, fertility preservation, gynaecological health conditions and sexual health.

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