Environmental chemicals may be to blame

The controversy over whether sperm counts have declined over the past 50 years is reopened by two papers in this issue of the BMJ. In a carefully analysed study of cohorts of unselected men in Britain born between 1951 and 1973, Irvine and colleagues demonstrate a progressive decline in sperm concentration and total sperm number per ejaculate of about 2% a year over 11 years.1 A smaller study by Bujan et al finds no change in sperm counts of sperm donors in the Toulouse area of France over a 16 year period.2

The controversy over sperm counts began with a metaanalysis by Carlsen et al which showed a decline in a sperm concentrations from 113 x 10⁶/ml to 66 x 10⁶/ml between 1940 and 1990.3 These findings were supported by Auger et al in a study of 1351 fertile men in Paris.4 …