The Male Fertility Doctor: Delaying Having Kids Is Impacting Your Future Kids! Dr Michael Eisenberg

Around 10% of the male genome is devoted to reproduction, so defects in sperm production often signal broader cellular or hormonal problems. Men with low semen quality and low testosterone have higher all-cause mortality and higher risks of conditions like cancer. Infertility should trigger a broader health evaluation (blood pressure, blood sugar, cholesterol, obesity) rather than being treated as a narrow, isolated problem.

Over the last 30–40 years, average paternal age has risen by about 3.5 years, with 'older fathers' (over 40) increasing from ~4% to ~9–10% of births. As men age, sperm counts and testosterone decline and sperm accumulate genetic mutations—around two new DNA mutations per year—raising the risk of longer time-to-pregnancy and child health issues. Women’s fertility declines more steeply after 30–35, but men do experience a meaningful, steady decline and more risky pregnancies with age.

Eisenberg points to data linking higher blood levels of phthalates (in many creams and lotions), bisphenol A/BPA (in plastics), microplastics, and other endocrine-disrupting chemicals with lower testosterone and poorer semen parameters. Animal experiments and human biomonitoring studies (like NHANES) show consistent correlations, even if not every study agrees. He avoids plastic bottles for his children and recommends glass/metal containers, noting plastic water bottles are a major exposure source.

Obesity lowers sperm counts and testosterone via increased heat insulation and hormonal conversion of testosterone to estrogen in fat tissue. Sedentary work (e.g., drivers), frequent saunas/hot tubs, prolonged cycling >5 hours/week, laptops on laps, and possibly phones between the legs can all impair sperm. Moderate alcohol (1–2 drinks/day) usually isn’t strongly harmful, but higher intake and certain genetic variants (ALDH2 ‘flushing’ mutation) clearly damage sperm motility. Sleep has a U-shaped relationship with semen quality: too little or too much is harmful, with ~7–9 hours optimal.

Population data show average male testosterone has dropped 50–100 ng/dL over recent decades, and levels naturally fall ~1% per year after age 20. However, giving testosterone to men with normal levels or modestly low levels (e.g., ~250–300 ng/dL) does not reliably improve energy, libido, or mood. Exogenous testosterone shuts down the body’s own production and often drives sperm counts to near-zero; WHO has explored using it as a male contraceptive. Side effects include hair loss, acne, gynecomastia, increased hematocrit, and potential permanent dependence if used long-term or abused when young.