Hormones play a pivotal role in human milk production. The main hormone responsible for milk production, prolactin, is essential for breast-feeding, as it stimulates milk production. But prolactin production and milk let-down also rely on a number of other hormones. Without the proper balance and interplay between a number of hormones, prolactin can’t perform its essential function.
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While prolactin is produced primarily by the anterior pituitary, cells in the brain and the tissues of the uterus during pregnancy also produce prolactin. The master gland of the body, the hypothalamus, normally suppresses prolactin production. Dopamine released from the brain signals the hypothalamus when to suppress prolactin production. Estrogen, the dominant female hormone, also appears to play a part in the increased levels of prolactin produced during pregnancy. Both thyroid-stimulating hormone and gonadotropin-releasing hormone also help regulate prolactin production. Prolactin is released in response to nipple and breast stimulation.
Prolactin plays two roles in breast-feeding. Its first role is to promote the development of alveoli in the breast. Alveoli are the milk-secreting bunches of cells found within breast tissue. Prolactin also stimulates milk production after birth in conjunction with two other hormones, insulin and cortisol. Oxytocin, another hormone, aids in the let-down reflex, which allows milk to flow from the alveoli when the infant nurses. Prolactin also inhibits ovulation in the nursing mother, which is why you may not have a menstrual period while breast-feeding.
Abnormal Prolactin Production
Conditions such as pituitary tumors, hypothyroidism or problems with the hypothalamus can elevate prolactin levels. Certain medications, such as antidepressants, estrogen or antipsychotics, can also artificially raise prolactin levels. Kidney disease and chest wall trauma can also induce high prolactin levels.
In women who are not pregnant, prolactin levels normally fall below 25 nanograms per milliliter. During pregnancy, prolactin levels rise to 200 ng/mL by the ninth month of pregnancy, International Board Certified Lactation Consultant Kelly Bonyata reports on her website, KellyMom. During the first three months postpartum, levels fall to 100 ng/mL in breast-feeding women. In women who do not breast-feed, prolactin levels fall to normal range within one week on average. By six months after giving birth, levels in breast-feeding moms fall to 50 ng/mL. Prolactin levels tend to increase at night and double in response to suckling.