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Luteinizing Hormone

Luteinizing hormone (LH) is a hormone involved in the proper function of the body’s reproductive system of both men and women. LH is a gonadotropin synthesized in the anterior pituitary gland and acts on the gonads (female ovaries and male testes) to boost their activity and sex hormones production like progesterone, estrogen, and testosterone. The hypothalamus which is another endocrine gland in the brain next to the pituitary gland secretes gonadotropin-releasing hormone (GnRH) which stimulates LH and follicle-stimulating hormone (FSH) release from the pituitary gland. Both LH and FSH are in constant pulsatile secretion to maintain homeostasis in the blood.

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The function of luteinizing hormone in women

Levels of LH are low throughout the menstrual cycle and sharply increase towards the end of the first half of the cycle to reach a peak and trigger ovulation. Once ovulation is triggered, fertility is at its highest, and after the peak, LH levels decrease again by negative feedback from estrogen and progesterone secretion. Whether fertilization occurs or not, LH levels will drop after ovulation.

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The function of luteinizing hormone in men

During puberty, LH levels increase to stimulate sexual maturity and remain stable throughout life. LH’s function in men is to boost testes’ testosterone production and consequently full sperm development to reach fertility.

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Meaning of different luteinizing hormone levels

Age, sex, and the timing in the female menstrual cycle dictate what is a normal LH level:

- Normal levels in women: 5-25 UI/L with a sharp increase towards mid-cycle. And 14.2-52.3 IU/L after menopause.
- Normal levels in men: 1.8-8.6 IU/L and they are steady through life in healthy patients.

LH levels can sometimes fluctuate outside the normal range and will either decrease or increase, each having different causes and implications depending on the gender. Testing for LH level is done in concordance with FSH levels by drawing blood samples with lab kits. The test is ordered when the physician needs to investigate the reason behind irregular menstruation, inability to conceive, delayed or early puberty, or change in libido.

High & Low LH in Male or Female

High LH in women

If LH remains high through the menstrual cycle, it means no ovulation is occurring; this could either be due to the natural process of menopause or due to a dysfunction of ovaries in younger individuals. Polycystic ovary syndrome (PCOS) is another condition associated with high LH levels, and it affects around 1 in 10 women worldwide. Whatever the condition, elevated LH causes infertility.

Low LH in women

Increased LH levels are due to a primary ovarian disorder, but in the case of decreased LH levels, the ovarian disorder is secondary to scarcity of LH. Eating disorders that lead to malnutrition, like anorexia or bulimia, are associated with a deficiency due to endocrine disruption. In the case of a pituitary disorder like hypopituitarism, the gland will fail to produce enough of multiple hormones including LH.

High and low LH in men

Just like in women, a surplus of LH is due to a primary gonadal disorder. A testicular dysfunction due to cancer treatment with either chemotherapy or radiotherapy causes an elevation of LH due to cellular damage. Chronic kidney disease and renal failure have been linked to high LH concentrations due to secretory dysregulation. Excessive alcohol consumption, either acute or chronic, has also been associated with hypogonadism and increased LH. Pituitary gland dysfunction affects men as much as women; the dip in LH due to hypopituitarism causes a decrease in testosterone affecting sexual drive and fertility.

How to treat high luteinizing hormone

The treatment for high LH levels is not a straightforward matter, there is no specific therapy that directly targets LH, but a combination of lifestyle and dietary changes has been shown to have a positive effect on its reduction. For example, hypersecretion of LH is typically found in obesity and is particularly found in obese individuals who fail to conceive and in PCOS patients. Weight loss through dietary restriction and regular exercise has been evidenced to have a positive impact on fertility by decreasing LH and FSH secretion. Since weight loss is correlated with improved insulin resistance, which is a main clinical aspect of PCOS, overweight PCOS patients may be advised to start there to improve their fertility.

How to treat luteinizing hormone deficiency

Treatment of low LH will depend on the cause of the deficiency and its consequences.
 There are multiple ways on how to increase LH; treatment will either target LH levels directly or make up for the lack of LH by targeting other processes.
 Infertility in both men and women can be managed with gonadotropin therapy which may complement other procedures assisting fertility like intrauterine insemination or in-vitro fertilization.
 Gonadotropin treatment in women can either be an injectable LH and FSH combination or FSH single therapy, or menotropin (human menopausal gonadotropin hMG) therapy which targets both FSH and LH secretion. It is recommended second in line in patients who fail to conceive after conventional hormone targeted therapy with clomiphene or letrozole, and it is recommended first-line in patients with resistant PCOS.
 Due to the risk of multiple gestations and ovarian hyperstimulation syndrome, it is now advised to follow a low-dose regimen of gonadotropin injections, which is as effective as regimens with higher doses.
 Gonadotropin therapy in infertile men is preferred over pure testosterone therapy due to testosterone’s side effects which can decrease LH levels. Human chorionic gonadotropin (hCG) and human menopausal gonadotropin (hMG) are both injections that can target LH and FSH deficiency. This therapy will result in improved spermatogenesis and testosterone production, thus treating infertility.

Conclusion

Luteinizing hormone is one of the two main gonadotropin hormones whose functions are to induce puberty and sexual maturation and to maintain fertility both in men and women. The natural course of LH secretion in healthy individuals is an increase during puberty then homeostasis throughout adulthood or until menopause is reached.
Certain conditions specific to age and gender will either cause a surplus or a deficiency in LH resulting in infertility. The treatment of these LH level fluctuations will depend on the underlying cause and will either directly target LH or manage the different dysregulations involved, with the main goal of assisting fertility.