Levine et al. 2017 — Temporal trends in sperm count

What the study did

Levine and colleagues pooled 185 studies covering 42,935 men and applied meta-regression to test whether sperm counts had changed over time, separating genuine trends from differences in method and sample. ^[1]

What it found

Among Western men not selected for fertility problems, sperm concentration fell 52.4% between 1973 and 2011 (about 1.4% per year). ^[1] The authors' 2022 update widened the data to every continent and ran it through 2018, reporting that "overall, SC declined appreciably between 1973 and 2018" — i.e. the decline is global and continuing. ^[2]

Why it matters — and its limits

It is the most-cited evidence for a real, sustained fall in sperm counts. But it measures sperm concentration, not demonstrated infertility, and it does not identify a cause. It is the backbone of the check is sperm count declining? and the statistic −52% sperm concentration.