The Global Decline in Sperm Count and Testosterone Levels: Trends, Mechanisms, and Environmental Drivers

Male reproductive health has experienced an unprecedented decline over the past five decades, characterized by substantial reductions in sperm count and testosterone levels. This review provides a comprehensive synthesis of current evidence on the global decline in sperm count and testosterone levels, examining epidemiological trends, underlying mechanisms, environmental drivers, and clinical implications. Sperm concentration declined by 51.6% globally between 1973 and 2018, with an accelerating trajectory post-2000 (from 1.16% to 2.64% per year). Concurrently, multiple independent studies document an age-independent secular decline in testosterone, averaging 1-2% per year across diverse populations. The etiology is multifactorial, involving endocrine-disrupting chemicals (bisphenol A, phthalates, pesticides, dioxins), lifestyle factors (obesity, sedentary behavior, smoking, heat exposure), and disruption of the hypothalamic-pituitary-gonadal axis. At the cellular level, mechanisms include Sertoli and Leydig cell dysfunction, oxidative stress, mitochondrial impairment, and sperm DNA fragmentation. Integrated clinical management combining lifestyle optimization, antioxidant therapy, and targeted endocrine interventions is essential. Prevention through environmental policy and public health initiatives represents the most promising long-term strategy.