Why Is Male Fertility Crashing Globally? - Dr Michael Eisenberg

The Decline in Global Sperm Counts

Dr. Eisenberg opens by confirming that global sperm counts have indeed declined by over 50% in the last 40 years, a finding that has gained increasing consensus in recent years despite initial controversy. The seminal study from the 1990s sparked widespread attention but also debate due to regional variations in semen quality and evolving methodologies in sperm analysis. For example, within the United States, sperm quality varies significantly between regions such as New York and the Midwest, though the exact causes remain unclear. Advances in laboratory and statistical techniques have since strengthened the evidence, with more recent studies in 2017 and 2023 solidifying the consensus that sperm counts are falling at an accelerating rate—approximately 1% per year over the last 50 years, increasing to about 2% annually in the past two decades.

Potential Causes: Environmental and Lifestyle Factors

The reasons behind this rapid decline are complex and unlikely to be genetic, given the pace of change. Dr. Eisenberg emphasizes environmental exposures as prime suspects, particularly endocrine-disrupting chemicals found in plastics, pesticides, and other pollutants. Microplastics, for instance, have been detected ubiquitously in both animal and human testicular tissue, raising concerns about their impact on sperm production and quality. While plastics themselves may be inert, the associated chemicals often have hormone-disrupting or carcinogenic properties. Studies have shown correlations between higher microplastic levels and poorer semen parameters such as count, motility, and morphology.

Lifestyle factors also play a significant role. Although modern men may be less sedentary than before, rising obesity rates and exposure to harmful substances like tobacco and excessive alcohol contribute negatively. Dr. Eisenberg advises men to adopt heart-healthy habits—balanced diets rich in whole grains, fruits, and vegetables, regular exercise, and minimizing exposure to harmful chemicals, including those found in certain skincare products and plastic packaging. However, he cautions against alarmism, noting that anxiety itself can impair sperm production, creating a vicious cycle.

Understanding Sperm Count and Male Fertility

The podcast clarifies what is meant by “sperm count” in clinical terms. Semen analysis measures several parameters: volume, concentration (millions of sperm per milliliter), motility (movement), and morphology (shape). While all are important, the decline in sperm count primarily refers to the concentration and total number of sperm. Other parameters like morphology and motility are more challenging to standardize over time due to evolving definitions and measurement techniques.

Dr. Eisenberg explains that sperm count is a key indicator of male fertility but not a perfect predictor. Fertility is a numbers game to some extent, with men typically having 50 to 100 million motile sperm, and a minimum of 20 to 40 million motile sperm generally needed for natural conception. Below these thresholds, assisted reproductive technologies such as intrauterine insemination (IUI) or in vitro fertilization (IVF) become necessary. Importantly, fertility is a “team sport,” with female partner factors also playing a crucial role.

Male Fertility as a Biomarker of Overall Health

One of the most striking points Dr. Eisenberg makes is the strong correlation between semen quality and general health. Men with conditions like hypertension, diabetes, obesity, and high cholesterol tend to have poorer sperm quality. Conversely, low sperm quality predicts higher risks of serious health issues later in life, including testicular and prostate cancers, heart disease, diabetes, and even increased mortality. A large Danish cohort study showed that men with lower semen quality had a shorter lifespan by three to five years compared to those with better sperm parameters.

This relationship suggests that sperm quality is not just about reproduction but serves as a “sixth vital sign,” reflecting genetic fitness and overall physiological well-being. Even men who appear outwardly healthy but have low sperm counts may harbor undiagnosed health problems or underlying biological vulnerabilities.

Clinical Evaluation and Common Causes of Low Sperm Quality

When men present with fertility concerns, Dr. Eisenberg describes a comprehensive evaluation process that includes reproductive history, physical examination, hormone testing, and assessment of exposures such as medications and lifestyle factors. A common finding is the presence of varicoceles—dilated veins in the scrotum that impair temperature regulation and toxin clearance, negatively affecting sperm production. Varicoceles are present in about 15% of men and cause fertility problems in roughly a quarter of those cases.

Treatment of varicoceles is typically surgical and outpatient, with improvements in sperm quality seen in about 70% of cases over a few months. However, decisions about surgery versus moving directly to assisted reproduction depend on individual circumstances, including the couple’s timeline and preferences.

Other interventions include hormone optimization, particularly for men with low testosterone or hormonal imbalances, vasectomy reversals, and surgical sperm retrieval for men with azoospermia (no sperm in ejaculate). These procedures, while sometimes daunting, often have good outcomes and can restore fertility or enable assisted reproduction.

The Role of Age in Male Fertility and Reproductive Health

Dr. Eisenberg discusses how male fertility declines gradually with age, starting from the late teens or early twenties. Although men can biologically father children into their 80s and beyond, sperm quality, volume, and testosterone levels decrease over time. Older paternal age is associated with increased risks of rare genetic disorders and conditions such as autism in offspring, though these risks remain relatively low on an individual level.

Interestingly, paternal age also influences the sex ratio of offspring, with older men slightly more likely to father female children. This phenomenon may be related to selective fetal loss or sperm-level factors, though the exact mechanisms remain unclear.

Advances in Reproductive Technologies and the Future

The podcast highlights the revolutionary impact of technologies like intracytoplasmic sperm injection (ICSI), which allows men with very low or no sperm in their ejaculate to father biological children by injecting a single sperm directly into an egg. The use of IVF and related technologies has increased, now accounting for about 2% of births in the U.S., driven by declining fertility and social trends toward delayed parenthood.

Looking ahead, Dr. Eisenberg touches on emerging possibilities such as in vitro gametogenesis (IVG), where sperm and eggs could be generated from skin cells, potentially allowing embryo selection to avoid genetic diseases or undesirable traits. While promising, these technologies raise ethical questions and societal implications.

Testosterone, Erectile Dysfunction, and Sexual Health

The discussion also covers the parallel decline in testosterone levels observed over recent decades, linked to obesity, environmental factors, and lifestyle. Testosterone is crucial for sperm production and sexual function, but supplementation must be carefully managed as exogenous testosterone can suppress sperm production.

Erectile dysfunction (ED) is primarily caused by vascular issues related to metabolic syndrome—hypertension, diabetes, obesity, and smoking—rather than psychological factors, which account for about 10% of cases. Medications like sildenafil (Viagra) and tadalafil (Cialis) improve blood flow and are effective treatments, but ED can also serve as an early warning sign for cardiovascular disease.

Psychological factors, including stress and anxiety, play a significant role in sexual function. The brain’s stress response can inhibit erections, a mechanism rooted in evolutionary survival instincts. Pornography use has been linked in some studies to ED due to altered sexual conditioning, though susceptibility varies among individuals.

Sleep quality and stress management are emphasized as important contributors to both testosterone levels and sperm quality, with a U-shaped relationship observed between sleep duration and fertility.

Practical Advice and the Importance of Awareness

Dr. Eisenberg advocates for men to be proactive about their reproductive health by obtaining baseline semen analyses and hormone testing early, even before fertility issues arise. Lifestyle modifications—regular exercise, healthy diet, avoiding smoking, moderating alcohol, managing stress, and prioritizing sleep—are foundational to maintaining reproductive and overall health.

He stresses the importance of destigmatizing male reproductive health issues, encouraging men to seek medical evaluation and openly discuss concerns. The growing awareness and acceptance, aided by public figures and comedians, are helping to break down barriers and improve outcomes.