Dr. Shanna Swan on fertility: what the evidence says · JRE #1638
SUBJECT: FERTILITY
Not a true/false call. Every claim is logged with its sources; read the exhibits below.
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 says 01 / RECORD
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.