HAVE SPERM DENSITIES DECLINED - A REANALYSIS OF GLOBAL TREND DATA

In 1992 a worldwide decline in sperm density was reported; this was qu ickly followed by numerous critiques and editorials. Because of the pu blic health importance of this finding, a detailed reanalysis of data from 61 studies was warranted to resolve these issues. Multiple linear regression models (controlling for abstinence time, age, percent prov en fertility, specimen collection method, study goal and location) wer e used to examine regional differences and the interaction between reg ion (United States, Europe, and non-Western countries) and year. Nonli near models and residual confounding were also examined in these data. Using a linear model (adjusted R-2 = 0.80), means and slopes differed significantly across regions (p = 0.02). Mean sperm densities were hi ghest in Europe and lowest in non-Western countries. A decline in sper m density was seen in the United States (studies from 1938-1988; slope = (-)1.50; 95% confidence interval (CI), (-)1.90-(-)1.10) and Europe (1971-1990; slope = (-)3.13; CI, (-)4.96-(-)1.30), but not in non-West ern countries (1978-1989; slope = 1.56; CI, (-)1.00-(-)4.12). Results from nonlinear models (quadratic and spline) were similar. Thus, furth er analysis of these studies supports a significant decline in sperm d ensity in the United States and Europe. Confounding and selection bias are unlikely to account for these results. However, some intraregiona l differences were as large as mean decline in sperm density between 1 938 and 1990, and recent reports from Europe and the United States fur ther support large interarea differences in sperm density. Identifying the cause(s) of these regional and temporal differences, whether envi ronmental or other, is dearly warranted.