Testosterone is a steroid hormone primarily synthesized in the testes in men and the ovaries and adrenal glands in women. While it plays a major role in the male body, it is also produced in women in smaller amounts. This hormone helps maintain muscle mass, supports bone density, and regulates sex drive in both sexes. Testosterone levels are not static; they follow a distinct chronological pattern throughout a person’s life.
Testosterone Levels During Development
The first major surge occurs during fetal development. Testosterone production starts around the seventh week of gestation in male fetuses, triggered by the sex-related gene on the Y chromosome. This early exposure is necessary for the differentiation of male internal and external reproductive organs.
A second, temporary surge known as “mini-puberty” occurs in infancy, typically within the first few months after birth. Levels rise dramatically, peaking around one to three months of age before declining to low, childhood levels by about six months. This brief activation of the reproductive axis is important for the maturation of the sex organs and for programming future reproductive capacity.
The third and most dramatic rise occurs during adolescence, marking the onset of puberty. This surge accelerates growth, deepens the voice, promotes the growth of facial and body hair, and increases muscle mass.
The Age of Peak Production
Testosterone levels reach their absolute maximum during the late teenage years, often peaking around age 18 to 20. While the absolute peak may be a single moment, the years immediately following it constitute the “peak plateau” of production.
For most men, this period of optimal, sustained high levels extends from the late teens through the early 30s. During this decade and a half, the body maintains the physiological benefits associated with high testosterone, including optimal muscle strength, maximum bone mineral density, and the most robust reproductive function. Even within this peak window, levels fluctuate daily, typically being highest in the morning and lowest in the evening.
Gradual Decline and Hormonal Changes
The natural, age-related decline in testosterone production begins after the peak plateau, typically starting around age 35 to 40. This change is not a sudden drop but a slow, continuous reduction over the rest of a man’s life. The rate of decline is consistently estimated to be about 1% to 2% per year for total testosterone.
This gradual reduction means that a man in his late 60s or 70s may have levels significantly lower than he did in his 20s. The slow decrease can lead to subtle, progressive changes sometimes grouped under the term late-onset hypogonadism. Common symptoms include a decrease in energy, a reduction in libido, loss of muscle mass, and an increase in body fat.
While the term “andropause” is sometimes used, the process is unlike the abrupt hormonal shift of menopause in women, as the decline is much slower and develops over many years rather than months.
Factors Influencing Baseline Testosterone
While age dictates the overall trajectory of testosterone levels, various lifestyle and environmental factors determine an individual’s specific baseline.
Stress and Sleep
One of the most significant suppressors is chronic stress, which causes the sustained elevation of the stress hormone cortisol. High cortisol levels directly inhibit the body’s ability to produce testosterone. The quality and quantity of sleep are also powerful modifiers, as production aligns with the body’s circadian rhythm. A lack of restorative sleep can negatively impact testosterone levels.
Body Composition and Activity
Body weight plays a role, as obesity is associated with lower testosterone because fat cells convert testosterone into estrogen, reducing the available amount. Dietary choices and physical activity are also relevant. A balanced diet rich in micronutrients supports hormone synthesis. Resistance training is known to stimulate testosterone production in the short term and helps maintain healthy levels over time. Conversely, a sedentary lifestyle or certain micronutrient deficiencies can contribute to sub-optimal testosterone levels.