Luteinizing Hormone (LH):

Luteinizing hormone (LH) is a gonadotropin hormone produced by the anterior pituitary gland. It plays a central role in reproductive function in both males and females.

In females, LH triggers ovulation and stimulates the corpus luteum to produce progesterone.

 In males, LH stimulates Leydig cells in the testes to produce testosterone.

Abnormal LH Levels: High or Low

High LH levels often occur when the gonads (ovaries or testes) are failing to produce adequate sex hormones. Causes may include primary ovarian insufficiency, menopause, Turner syndrome, or testicular failure. In women with PCOS, LH is also often disproportionately elevated compared to FSH.

Low LH levels occur when the hypothalamus or pituitary is not functioning properly, resulting in insufficient stimulation. Causes include hypothalamic suppression (e.g., from anorexia, extreme stress, excessive exercise), pituitary tumors, hyperprolactinemia, Kallmann syndrome, or use of medications like opioids and steroids.

Symptoms of LH Imbalance

In females, LH imbalance can cause irregular or absent periods, infertility, anovulation, hot flashes, low estrogen symptoms such as vaginal dryness or mood swings.

In males, low LH may lead to decreased libido, erectile dysfunction, reduced facial and body hair, infertility, fatigue, and low testosterone levels.

What Happens When LH Is Abnormally Low: Systemic Effects

Luteinizing hormone (LH) is a key signal from the brain, that stimulates the production of sex hormones—primarily estrogen and progesterone in women, and testosterone in men. When LH is deficient or suppressed, it disrupts sex hormone production, triggering widespread effects throughout the body.

Cardiovascular System: Low LH results in low levels of estrogen or testosterone, which removes their normal protective effects on the heart and blood vessels. Estrogen helps maintain healthy cholesterol levels, vascular flexibility, and blood pressure, while testosterone supports vascular tone and endothelial function.

As a result, LH deficiency is associated with:

• Elevated LDL (“bad” cholesterol)
• Reduced HDL (“good” cholesterol)
• Increased blood pressure
• Insulin resistance and metabolic syndrome
• Higher risk of heart attack and stroke

 Skeletal System: LH deficiency leads to decreased production of sex hormones, especially estrogen and testosterone, both of which are essential for maintaining bone strength.

The downstream effect is:

• Decreased bone mineral density
• Increased bone resorption
• Higher risk of osteopenia, osteoporosis, and fractures, particularly in postmenopausal women and aging men

 Metabolic System: Low LH contributes to hypogonadism, which alters body composition and metabolism.

This can result in:

• Increased fat storage, especially visceral fat
• Loss of lean muscle mass
• Insulin resistance
• Higher risk of developing type 2 diabetes and fatty liver disease

 Skin, Hair, and Secondary Sex Characteristics: Sex hormones influence hair growth, skin hydration, and tissue elasticity. Low LH → low estrogen or testosterone may lead to:

• Dry, thinning skin
• Hair thinning or loss
• Reduced facial and body hair (in men)
• Vaginal dryness and breast tissue shrinkage (in women)
• Decreased muscle definition
  

 Reproductive System: In the reproductive system, LH is critical for ovulation in females and testosterone production in males.

Low LH leads to:

• Females:
• Amenorrhea (absence of menstrual periods)
• Anovulation and infertility
• Reduced libido and early onset menopausal symptoms
• Males:
• Low testosterone and erectile dysfunction
• Reduced sperm production and infertility
• Testicular atrophy
• Low libido and decreased sexual satisfaction

 Immune System: Sex hormones modulate immune balance. When LH is low and hormone levels drop, the body's ability to regulate inflammation may become impaired.

This results in:

• Increased pro-inflammatory markers (e.g., CRP, IL-6)
• Higher susceptibility to chronic inflammation
• Potential increased risk of autoimmune disorders

Estrogen, in particular, has anti-inflammatory and immunomodulatory effects, while testosterone plays a role in immune surveillance and repair.

LH plays a central role in hormonal signaling. When LH is persistently low, it disrupts sex hormone production and leads to a wide array of health consequences across nearly every system.

Understanding the Role of LH in PCOS

Polycystic Ovary Syndrome (PCOS) is one of the most common hormonal disorders affecting women of reproductive age. While it is often associated with irregular periods, acne, and fertility issues, one of the lesser-known aspects of PCOS is its connection to the hormone luteinizing hormone (LH).

In many women with PCOS, LH level is chronically elevated, and this plays a key role in the underlying hormonal imbalance.

This leads to an imbalanced LH-to-FSH ratio, often greater than 2:1 or even 3:1. The elevated LH levels overstimulate the ovarian theca cells, resulting in the overproduction of androgens, such as testosterone.

This excess androgen production contributes to many of the classic symptoms of PCOS: acne, oily skin, unwanted facial or body hair growth (hirsutism), and sometimes scalp hair thinning or loss. Importantly, the hormonal imbalance caused by high LH and androgens interferes with the normal maturation of follicles in the ovaries. As a result, ovulation often fails to occur, which leads to irregular or absent menstrual periods and infertility. Over time, these immature follicles can accumulate in the ovaries, giving them a "polycystic" appearance on ultrasound.

Not all women with PCOS will have elevated LH levels, but it is a common pattern, particularly in lean women with PCOS or those with a more classic hormonal presentation. Measuring LH and FSH levels can help support the diagnosis, especially when paired with symptoms of androgen excess and irregular cycles.

Understanding the role of LH in PCOS also opens up treatment opportunities. Medications that lower LH or reduce androgen production—such as combined oral contraceptives, metformin (which improves insulin sensitivity), or ovulation-inducing agents like letrozole—can help restore hormonal balance and ovulation. Lifestyle changes, particularly those that target blood sugar regulation and weight management, are also effective ways to indirectly lower LH and androgens.

In summary, while PCOS is a complex condition with multiple contributing factors, elevated LH plays a central role in disrupting ovulation and increasing androgen levels. Recognizing and addressing this hormonal imbalance can lead to more effective, targeted treatments—helping women with PCOS reclaim their cycles, fertility, and overall well-being.