Prolactin is a hormone produced by the pituitary gland in the brain. Concentrations of prolactin are regulated by the chemical, dopamine. It is usually present in small amounts in men and women who are not pregnant. The main role of prolactin is to produce milk and so the hormone is found in high concentrations in pregnant women.
Throughout pregnancy and for a while after childbirth, prolactin concentrations are high. The development of milk is stimulated by the hormones prolactin, oestrogen and progesterone. Once the child is born, prolactin continues to stimulate the production of breast milk and maintains its supply. If a mother decides not to breastfeed, her prolactin levels will naturally decrease. However, the suckling motion of the infant is what stimulates the production of prolactin. If the mother continues to breastfeed, her prolactin levels will remain high.
A further cause of high prolactin levels is a prolactinoma or a prolactin-producing tumour found on the pituitary gland. The symptoms can include:
Men with a prolactinoma can be at an increased risk of developing cardiovascular disease.
High levels of prolactin are also seen in individuals with macroprolactin. This occurs when prolactin clumps together. This causes high levels to be measured. Macroprolactin is biologically inactive and therefore causes no clinical symptoms.
Low levels of prolactin can be a sign of a decreased pituitary function or a reduced hormone production. However, these cases are not usually treated. Other drugs can also cause low levels of prolactin such as dopamine, levodopa and ergot alkaloid derivatives.
Although high circulating levels of prolactin are normal in pregnant women, in men and non-pregnant women high levels may indicate an underlying health condition. Similarly, a low level could indicate pituitary gland dysfunction. Making sure your diet is healthy and you are getting adequate exercise can help to prevent adverse health events.
Prolactin concentrations have been shown to be dependent on the amount of dietary protein consumed. The mammary glands in the breasts need an active uptake of amino acids to produce milk. Therefore, an increased protein/carbohydrate ratio causes an increase in the uptake of amino acids which can result in an increased prolactin level.
There is evidence that there are significant benefits of regular exercise on overall fitness, the cardiovascular system, health-related quality of life and nutritional parameters.
However, exercise has major benefits for our wellbeing too. Exercise can help to reduce the symptoms of depression, self-esteem and anxiety.
We should all aim for around 150 minutes of aerobic exercise per week. Activities may include jogging, walking, swimming, cycling, exercise classes, sports matches or tennis.
 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.
 Heiwe, S and Jacobson, S, H (2011). Exercise Training for Adults with Chronic Kidney Disease (Review). Cochrane Database of Systematic Reviews: 10.