Prolactin is a hormone produced by the pituitary gland, a small gland at the base of the brain. Present in both males and females, its most recognized role is stimulating breast development and milk production in women after childbirth. The pituitary gland’s production of prolactin is regulated by substances like dopamine and estrogen.
Prolactin Levels in Females by Life Stage
Prolactin levels in females undergo significant changes throughout life, driven by puberty, pregnancy, and menopause. These shifts reflect the hormone’s role in reproductive readiness and function.
Puberty
As girls enter adolescence, hormonal changes associated with puberty cause prolactin levels to fluctuate. During the initial stage of puberty, known as Tanner Stage I, levels are low, ranging from 3.6 to 12.0 nanograms per milliliter (ng/mL). As puberty progresses through Stages II, III, IV, and V, the range can shift to between 2.6 and 20.0 ng/mL, aligning more closely with adult levels.
Non-Pregnant Adult
For non-pregnant adult females, a stable prolactin level is maintained. Reference ranges fall between 3 and 30 ng/mL, although some labs may define the upper limit as 23 or 25 ng/mL. Levels can vary slightly during the menstrual cycle, with a small increase around the mid-cycle point.
Pregnancy
Pregnancy causes the most dramatic natural increase in prolactin levels to prepare the breasts for milk production. During the first trimester, levels rise significantly, with ranges between 34 and 213 ng/mL. This trend continues through the second trimester, reaching 110 to 330 ng/mL, and peaks in the third trimester, where levels can be anywhere from 137 to over 400 ng/mL.
Lactation and Post-Menopause
After childbirth, prolactin levels remain high to facilitate breastfeeding, often ranging from 80 to 400 ng/mL. The act of suckling stimulates the pituitary gland to release more prolactin, maintaining milk supply. If a mother does not breastfeed, prolactin levels return to the non-pregnant baseline within a couple of weeks. Following menopause, prolactin concentrations decrease to a range of 2.0 to 20.0 ng/mL.
Prolactin Levels in Males and Children
While known for its function in females, prolactin is also present in males and children, serving different purposes at different concentrations. Levels in these groups are lower and more stable compared to the dramatic fluctuations seen in females during pregnancy and lactation.
Infants and Pre-Pubertal Children
In infancy, from birth to one year, prolactin levels range from 3 to 25 ng/mL and remain low throughout early childhood. For pre-pubertal children, the range is between 3 and 20 ng/mL. Before puberty, there is little difference in prolactin concentrations between males and females.
Adult Males
In adult males, prolactin levels are consistently low, with a normal range falling between 2 and 18 ng/mL. While its functions are not as extensively defined as in females, prolactin in males is understood to play a part in reproductive health and can influence sex drive.
Factors Causing Natural Prolactin Fluctuations
Prolactin levels are not static and can be influenced by various daily activities and physiological states unrelated to disease. These short-term changes can affect the results of a blood test.
One of the most significant influences is the body’s natural sleep-wake cycle. Prolactin secretion increases during sleep, reaching levels two to three times higher than during the daytime. For this reason, healthcare providers recommend that blood samples for prolactin testing be taken in the morning after a period of fasting.
Physical and psychological stress can also cause temporary spikes in prolactin. Intense exercise, pain, or significant emotional distress can all lead to a transient rise. Food intake, particularly a protein-rich meal, can slightly elevate prolactin, as can sexual intercourse and nipple stimulation.
Understanding Abnormal Prolactin Levels
Persistently high levels, a condition known as hyperprolactinemia, are more common than abnormally low levels, termed hypoprolactinemia. The most frequent cause of significantly elevated prolactin is a benign, noncancerous tumor on the pituitary gland called a prolactinoma.
Hyperprolactinemia can interfere with reproductive health and cause various symptoms. In women, this may manifest as irregular or absent menstrual periods, infertility, or a milky discharge from the nipples when not pregnant or breastfeeding (galactorrhea). In men, symptoms can include erectile dysfunction, low libido, and breast enlargement.
Low prolactin levels are rare and often associated with an underactive pituitary gland, a condition called hypopituitarism. The primary sign of low prolactin is an inability to produce breast milk after giving birth. Because prolactin levels can be affected by many factors, it is important to consult a healthcare provider for an accurate diagnosis and to interpret any lab results.