Luteinizing hormone (LH) is a cornerstone of reproductive health, playing a pivotal role in both male and female reproductive systems. Produced by the anterior pituitary gland, LH is integral to the complex dance of hormones that underpin fertility, sexual development, and menstrual health.
This article seeks to explore the multifaceted functions of LH, from its critical involvement in the hypothalamic-pituitary-gonadal axis to its impact on ovulation, testosterone production, and beyond.
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What is the Luteinizing Hormone?
Luteinizing hormone is a glycoprotein that is produced by the anterior pituitary as part of the hypothalamic-pituitary-gonadal (HPG) axis. To fully comprehend the role LH plays in reproduction, it is important to first take a moment to better understand the HPG axis. This axis is a complex interplay of neurotransmitters and hormones that coordinate together to regulate reproductive hormones.
Think of the HPG axis as a production line for estrogen, progesterone, and testosterone. Its main players, the hypothalamus, the pituitary, and the gonads (ovaries and testes), work together to ensure that the correct amount of reproductive hormones are being produced. Therefore, when estrogen and testosterone levels in the body drop, this signals the HPG axis to increase production.
The hypothalamus responds by releasing gonadotropin-releasing hormone (GnRH) in a pulsatile fashion which sets the rhythm for the rate of production. When the beat is fast and frequent, production is spurred; when the beat is slow, production slows (2).
GnRH travels to the pituitary gland where its frequent pulses stimulate the release of LH and follicle-stimulating hormone (FSH). LH, along with FSH, then travels to the gonads to stimulate reproductive processes such as ovarian progesterone production in females and testosterone production from the testes in males. When production outpaces demand and estrogen, progesterone, and testosterone levels rise too high, they inhibit LH release by slowing down the pulsatile rhythm of GnRH, acting as part of a negative feedback loop that maintains hormonal homeostasis (2).
The Role of LH in Female Reproductive Health
LH and FSH set the stage for ovulation and thus play a critical role in the menstrual cycle and reproduction.
Ovulation and the Menstrual Cycle
LH and FSH work together to increase the production of estradiol from the ovarian follicle. LH starts the process by encouraging the production of androstenedione, an ovarian steroid, from the theca cells. FSH helps by producing the enzyme aromatase which converts androstenedione to estradiol (26). When estradiol levels are sustained at 200 pg/mL or more for at least 2 days, a positive feedback mechanism is employed in which the hypothalamus increases GnRH secretion, leading to an LH surge (2).
This surge prompts the maturation of the developing oocyte which then is released from the ovarian follicle approximately 24-36 hours later, a process called ovulation (35). LH test strips, commonly used for fertility planning, are testing for this LH surge as it coincides with the ideal ovulatory window for embryo production.
LH and Hormonal Regulation
LH’s role does not end with ovulation. After ovulation the follicle turns into the corpus luteum, a temporary organ that produces the hormones progesterone and human chorionic gonadotropin (hCG) which are important for pregnancy. LH stimulates the production of progesterone from the corpus luteum, leading to the rise in progesterone during the luteal phase of the menstrual cycle.
Progesterone helps to prepare the endometrium (uterine lining) for the implantation of a fertilized oocyte. If fertilization of the egg occurs, the corpus luteum will start to produce hCG maintaining the high levels of progesterone needed for proper implantation and early embryonic growth. If, however, no fertilization occurs by day 14 after ovulation, the corpus luteum breaks down and is reabsorbed back into the ovary. This results in the cessation of progesterone production which in turn causes the lining to shed as part of menstruation (29).
The Role of LH in Male Reproductive Health
LH is also vital to the male reproductive system through its stimulatory action on testosterone production.
Testosterone Production
LH plays an essential role in testosterone production and male sexual development via the development of Leydig cells. LH is released in pulses stimulated by GnRH action on the pituitary and travels to the testes where it attaches to receptors on the surface of Leydig cells. This binding stimulates the production of testosterone from the testes, which in turn is critical for sperm production, the development of secondary sex characteristics, and important psychological and metabolic effects (28). The Leydig cells also play a role in the urogenital development of male embryos through the release of androgens that induce this process (1).
Impact on Sperm Maturation
LH along with FSH is involved in the production and quality of sperm. By stimulating testosterone, LH initiates the process of sperm production. In the presence of testosterone, FSH acts on Sertoli cells in the testes which enables the maturation of sperm and overall sperm quality (28).
During puberty, LH pulse frequency increases, causing Leydig cells in the testes to multiply and mature. More Leydig cells lead to higher testosterone levels within the testes which is necessary for maintaining sperm production. Testosterone levels are kept in check by its inhibitory action on LH. When testosterone levels reach too high, the pulsatile frequency of GnRH slows down, lowering the stimulation of LH which in turn lowers the production of testosterone (26).
Luteinizing Hormone Imbalances
Despite the complex system of checks and balances within the HPG axis, imbalances sometimes occur leading to detrimental effects on reproductive wellness.
High LH Levels
As mentioned previously, LH production can be inhibited by high levels of circulating sex steroids such as testosterone and estrogen. Therefore, when LH levels are consistently high, there likely is insufficient sex steroid production coming from the ovaries or testicles, impacting reproductive processes and function.
In women, high LH levels are often implicated in polycystic ovarian syndrome (PCOS). Patients with PCOS lack the cyclical pattern of LH and FSH that maintains a healthy menstrual cycle. Instead, LH levels tend to be high while FSH levels are suppressed. This can lead to abnormal menstrual cycles and issues with fertility. In a study that followed PCOS patients who were experiencing fertility issues versus those who were not, LH levels were significantly higher in the infertile group.
One explanation for this is that the high LH levels correlated with poor oocyte quality and development, impacting embryonic development (35). During menopause, LH levels significantly increase and remain elevated as the ovaries no longer produce estradiol.
In men, high levels of LH can be a sign of primary hypogonadism in which the testes fail to produce adequate levels of testosterone. Low testosterone can lead to poor sperm production and poor sperm quality resulting in fertility issues. In addition, low testosterone levels can result in additional symptoms such as low libido, erectile dysfunction, depression, fatigue, and osteoporosis. Primary hypogonadism can be caused by genetic defects, testicular injury, chemotherapy, radiation, and excessive alcohol intake (12).
Low LH Levels
On the other end of the spectrum are low LH levels. These levels are often caused by issues at the hypothalamus or the pituitary rather than a loss of negative feedback from estrogen and testosterone. Low LH levels are found in male secondary hypogonadism, which like primary hypogonadism, is also correlated with low testosterone levels and thus is associated with similar symptoms. Low testosterone in this case results from the lack of LH stimulation of Leydig cells (12). Low LH levels can also be caused by insufficient energy intake, when caloric intake is outpaced by caloric loss such as through excessive exercise (34).
Testing for Luteinizing Hormone Levels
As LH plays a pivotal role in menstrual health, fertility, and sex hormone production, it can be an important indicator of dysfunction in these areas, and is often included in hormone test panels.
Indications for LH Testing
There can be many reasons why a provider would want to include LH testing as part of an overall hormonal assessment. Because LH imbalances can result in fertility issues in all genders, its testing can help pinpoint possible causes such as low spermatogenesis or irregular ovulation. LH testing along with serum testosterone levels can also help identify cases of hypogonadism in men experiencing symptoms of low testosterone (12). Although not enough to diagnose menopause on its own, LH levels can help indicate whether menopause status is likely.
Understanding LH Test Results
When using LH tests to help understand fertility or menstrual cycle issues in women, timing is important as LH fluctuates normally in a healthy menstrual cycle. Testing for fertility often starts in the middle of the follicular phase to catch the LH surge that indicates impending ovulation. In this case, an absent or deficient LH surge could indicate an anovulatory cycle. Monitoring the LH surge for changes can be used as a way to assess efficacy in fertility treatments.
LH testing is particularly important during the use of fertility-assisted reproductive technologies to help determine appropriate timing. When used to assess for menopause status, high levels of LH can indicate a positive likelihood, especially when accompanied by high FSH and low estradiol and progesterone levels.
In men, testing for LH in cases of low testosterone can help distinguish primary hypogonadism from secondary hypogonadism. In primary hypogonadism, LH levels are elevated while in secondary hypogonadism, LH levels are low to normal (12).
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Managing Luteinizing Hormone Imbalances
Treating LH imbalances involves finding the root cause of the issue to correct dysregulation. Depending on the underlying issue, medical treatments such as hormone therapy may be indicated, and/or dietary and lifestyle changes.
Medical Treatments
For fertility enhancement, the use of appropriately timed LH supplementation has been used to varying effect. While some studies suggest that LH supplementation during the second half of the follicular phase can help improve follicle quality and embryo production, thereby improving fertility outcomes, other studies demonstrated little to no improvement with LH supplementation. It may be that the efficacy of LH supplementation depends on specific populations, such as women over 35, and the concomitant use of other treatments such as FSH and gonadotropin.
Because the symptoms of both male primary and secondary hypogonadism stem from low testosterone, testosterone replacement therapy is an important treatment option to help alleviate these symptoms either as a monotherapy or as a larger comprehensive plan (12).
Lifestyle and Dietary Considerations
Diet can play an important role in LH production, especially in cases where undernourishment is present. When energy expenditure exceeds energy intake, the body interprets this as an unsafe situation in which to encourage reproduction. Therefore, reproductive processes are put on hold by slowing GnRH pulsation and with it, the stimulation of LH (34). A nutrient-rich diet that meets the energetic demands of the body can help maintain healthy LH levels. Additionally, improvements in semen quality occurred when men incorporated healthy levels of carbohydrates, fiber, and foods rich in lycopene and folate, suggesting indirect actions on LH (34).
A healthy exercise regimen is also vital. Moderate exercise can be beneficial to LH production, whereas prolonged high-intensity and high-weight-resistance exercises have been shown to decrease LH stimulation and testosterone levels in men for up to 12 hours. Additionally, excessive exercise has been linked to menstrual cycle irregularities and sometimes cycle cessation in women (34).
Mitigating lifestyle behaviors such as drinking alcohol, smoking, and stress is important as excesses of these have been shown to interfere with GnRH pulsation, thus causing dysregulation of the HPG axis, including altered LH levels (34).
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Key Takeaways
Luteinizing hormone (LH) plays a vital role in the orchestration of reproductive functions, facilitating crucial processes from ovulation in women to testosterone production in men. As a linchpin in the regulation of the menstrual cycle, fertility, and sexual development, balanced levels of LH are paramount for optimal reproductive health. Disruptions in LH levels can lead to a range of reproductive challenges, including polycystic ovarian syndrome (PCOS) and hypogonadism.
If you suspect an imbalance in your LH levels or face reproductive health issues, consulting with healthcare professionals can provide you with the guidance and treatments needed for managing your health proactively. Early detection and intervention can be key in navigating the complex interplay of hormones that support our reproductive systems, reinforcing the importance of attentiveness and care in maintaining our overall well-being.
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