Testosterone

TESTOSTERONE

Testosterone is the primary male sex hormone. It is produced predominantly (95%) in the Leydig cells in the testicles and, to a lesser extent, in the adrenal gland in both men and women. Women also produce small amounts of testosterone in the ovaries. Testosterone affects sexual attributes and development. It has significant effects throughout the entire body in both men and women. Testosterone affects the brain, bones and muscle mass, fat distribution, genital tissues, and sexual behavior. Testosterone is also referred to as the “anti-aging hormone” – testosterone deficiency is known to be a predisposing factor for premature death. Conversely, higher testosterone levels are linked to longer lifespans in men.

Testosterone is derived from cholesterol, the basic primary foundation of steroid hormone synthesis. Cholesterol-lowering drugs may impair normal testosterone production. However, cholesterol from food has not been linked to higher testosterone production. The primary factor in testosterone production regarding cholesterol is its delivery into the cell mitochondria. However, higher testosterone levels have been linked to higher HDL cholesterol levels in the blood.

Like cortisol, testosterone secretion follows a rigidly regulated negative feedback system. The hypothalamus secretes gonadotropin-releasing hormone (GnRH), which stimulates the pituitary gland to secrete two important hormones: luteinizing hormone (LH, see below) and follicle-stimulating hormone (FSH). In men, LH stimulates the secretion of testosterone in the testicles. In women, LH mainly stimulates the secretion of estrogen and progesterone. The testosterone produced is released into the blood. Most of this (98%) is biologically inactive (SHBG-bound) testosterone. The rest is biologically active (free) testosterone. SHBG releases testosterone as needed.

Like cortisol, testosterone levels secreted follow a daily cycle: the highest levels occur in the early hours of the morning and the lowest levels in the evening. Factors involved in testosterone production include diet and micronutrient intake, exercise, body weight, sleep, stress, environmental toxins and many pharmaceutical drugs.

Low testosterone levels may occur due to hypothalamus or pituitary gland disease, diabetes, alcoholism, physical testicular injury, malfunction, hyperprolactinemia, or genetic abnormality. Low testosterone levels may cause infertility, low libido, erectile dysfunction, low facial hair growth, reduced muscle mass, and breast enlargement in males (gynecomastia). Low testosterone levels are linked to increased visceral fat, insulin resistance, and a higher risk of cardiovascular diseases.

Excessive testosterone levels are usually associated with anabolic steroids or testicular or adrenal tumors in men. In women, they are typically linked to PCOS, congenital adrenal hyperplasia, or adrenal tumors. The sensitive testosterone method is especially useful in measuring female testosterone levels, which are more than 10 times lower than in males. Calculating the amount of free testosterone is crucial when determining the biologically active testosterone in the blood.