Dr. Shanna Swan on the Joe Rogan Experience #1638, fact-checked
“our sperm count, our miscarriage rates, our fertility rates, our testosterone levels, they're all going south, if you will, at the rate of about 1% per year”
What the evidence shows: Swan's own research (the Levine et al. meta-analyses she co-authored) does support a roughly 1%-per-year decline in sperm concentration among men in Western countries since the 1970s, a finding replicated in a 2022 update covering global data. Even so, the original authors describe the topic as still "controversial" given variability in study quality, the unselected-versus-fertile-population distinction, and the lack of a detectable decline outside Western cohorts in the earlier analysis. Evidence for parallel 1%-per-year declines in miscarriage rates, general fertility rates, and testosterone levels is considerably weaker: a comprehensive Lancet review of miscarriage epidemiology documents prevalence (about 15.3% of recognized pregnancies) and risk factors but does not report or support a uniform ~1%-per-year secular increase in miscarriage rates. Population-level testosterone studies (e.g., the widely cited Massachusetts cohort) found a modest but non-uniform decline not clearly tied to a fixed annual rate, and fertility-rate declines are well documented globally but are attributed by demographers primarily to social and economic factors (delayed childbearing, contraception access, economic conditions) rather than a specific 1%-per-year biological trend from endocrine disruptors. Collapsing these four distinct metrics, each with different data quality and different plausible causes, into one uniform "1% per year" figure overstates the certainty and generalizability of the evidence, even though the sperm-count component draws on real and repeatedly replicated research.
“And at that point, the median, that's the middle of the distribution, was 99 million sperm per milliliter.”
What the evidence shows: Swan's figures come from Levine et al. 2017 (Human Reproduction Update), a meta-regression of 185 studies covering 42,935 men, which reported sperm concentration among "Unselected" men in Western countries declining roughly 52% between 1973 and 2011 (unadjusted slope -0.70 million/mL/year), consistent with the 99-to-47 figures Swan cites. The finding remains genuinely contested rather than settled: critics note that combining studies using different counting methods and populations over five decades can introduce bias, that early studies may have overestimated baseline counts, and that publication bias could favor studies reporting declines. More recent analyses reach conflicting conclusions; a Cleveland Clinic-affiliated summary of a meta-analysis of American men found sperm concentration has been essentially stable or even rising slightly since 1970. The 2017 meta-analysis itself has not been retracted and remains widely cited by its authors, who have published a follow-up defending the methodology against these criticisms, but the underlying decline is still debated in the field. Overall, the raw numbers Swan quotes accurately reflect her own published meta-analysis, but whether they represent a genuine, uniform decline in male fertility remains an active and unresolved scientific debate.