Prolactin is a hormone produced by the pituitary gland in the brain and is involved in lactation. Although it is often present in non-pregnant males and females, prolactin’s main role is to produce milk. Hence, why it is found in large amounts in pregnant females. The concentration of prolactin in the body is regulated by the chemical, dopamine.
A prolactin blood test can be used alongside other tests to determine the function of the pituitary gland as well as using it as a diagnostic factor for infertility or irregular periods.
Low levels of prolactin are not usually a cause for concern, but high levels can be caused by several factors. In women, prolactin can affect the ability to conceive because it prevents the ovaries from making the hormone, oestrogen. While in men, high levels of prolactin can result in erectile dysfunction and loss of libido.
You can test your prolactin level along with other key fertility 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 prolactin including our Female Fertility and Male Hormones health checks.
Prolactin has a variety of roles in the human body, but the main one is to stimulate the mammary glands to produce milk. Female prolactin levels are increased throughout pregnancy and after childbirth, stimulating the production of milk for the new-born. The production of milk is stimulated by the hormone’s prolactin, oestrogen and progesterone. The increased concentration of the hormone in the blood causes the enlargement of the mammary glands, so they can prepare to produce milk. This usually, occurs when progesterone levels reduce towards the end of the pregnancy. The suckling motion of the baby also stimulates the production of milk. If the mother decides not to breastfeed, her prolactin levels will naturally fall, but continuing to breastfeed will maintain high levels of prolactin.
An increase in prolactin levels during pregnancy are normal and essential to produce milk. However, if there is a high level of circulating protein in the body when there is no pregnancy, it can affect the menstrual cycle or could be a symptom of oestrogen deficiency in females or testosterone deficiency in males.
A low level of prolactin in the blood may be normal and no cause for concern but it could also mean the pituitary gland is not functioning normally. Some medication can result in low prolactin levels, too.
If you are worried about your prolactin level or just want to check where you fall on the range, you can test your level with a simple at-home blood test.
Pregnancy is a major cause of increased prolactin levels in women. Another reason for increases in the hormone is a type of benign noncancerous pituitary gland tumour called a prolactinoma. They are the most common type of pituitary gland tumour and symptoms are either caused by too much prolactin in the blood or the pressure the tumour puts on the surrounding tissues.
Low levels of prolactin are often caused by a reduced pituitary gland function and a decreased production of hormones. They can also be caused by some medications such as dopamine, levodopa and ergot alkaloid derivatives.
Prolactinomas have been associated with an increased risk of developing cardiovascular disease in males.
Some of the symptoms associated with prolactinomas are:
Large tumours may also cause:
Low levels of prolactin are rare but it can lead to inadequate levels of milk being produced following childbirth.
High circulating levels of prolactin are normal in pregnant women but in non-pregnant men and women, high levels can indicate an underlying health condition or low levels may signify pituitary gland dysfunction. Your lifestyle may help to influence your hormone levels or could prevent adverse health events.
Research has shown that a diet high in protein and low in carbohydrates increases the uptake of amino acids needed to produce milk and thus, can result in increased prolactin levels in the blood. 
Protein can be acquired from both animal and plant-based sources. The following shows the amount of protein in grams per 100g provided by specific foods:
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 Lab Tests Online UK. (2014). Prolactin. Available at: https://labtestsonline.org.uk/tests/prolactin
 Toulis, K, A., Robbins, T and Reddy, N et al. (2017). Males with Prolactinoma are at Increased Risk of Incident Cardiovascular Disease. Clinical Endocrinology: 88, pp 71-76.
 Valázquez-Villegas, L, A., López-Barradas, A, M and Torres, N et al. (2015). Prolactin and the Dietary Protein/Carbohydrate Ratio Regulate the Expression of SNAT2 Amino Acid Transporter in the Mammary Gland During Lactation. Biochimica et Biophysica (BBA)-Biomembranes: 1848(5), pp 1157-1164.
 British Nutrition Foundation. (2019). Protein. Available at: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/protein.html?start=4