Abstract
The debate concerning the possible degradation in human sperm quality began in the 1970s, was revived at the beginning of the 1990s and has continued to mobilize the scientific community ever since. After the meta-analysis by Carlsen et al. (1992) showing a decline in human semen quality over the last 50 years, several groups investigated the sperm characteristics of more or less homogeneous groups of men who had provided semen at the same center for 10 to 20 years. A significant decrease in sperm concentration was reported in some studies, but not in others. Meanwhile, there is an increasing number of reports suggesting that physical and chemical factors introduced and spread by human activity in the environment may have contributed to sperm decline. At the end of the 20th century the debate on declining semen quality is not closed. The lack of certainty and the serious consequences that such a decline would have on the fertility of human populations make this an important public health issue at the start of the 21st century. For this reason, intensive research should be developed in both fundamental and epidemiological domains, particularly in South America, where industrial and agricultural pollution pose a serious threat to the population.
Highlights
Resumo O debate sobre o possível declínio na qualidade dos espermatozóides humanos começou nos anos 70, foi reativado no início dos anos 90 e continua mobilizando a comunidade científica desde então
All the studies claiming a decline in semen quality are retrospective and it always can be said that prospective studies in the general population would be much better
One of the predictable consequences of a possible decrease in sperm quality in humans is an increase in the number of infertile couples
Summary
There has been continuous debate concerning the possible decrease in sperm quality in the last few decades since the publication of a study by Nelson & Bunge (1974). From until 1992, several authors reported such changes but were unable to establish a clear cause (Bendvold, 1989; Bendvold et al, 1991; Bostofte et al, 1983; James, 1980; Leto & Frensilli, 1981; Menkveld et al, 1986; Osegbe et al, 1986; Osser et al, 1984; Smith et al, 1978). Conclusions were drawn from highly selected populations or populations of individuals seeking medical help for infertility. An observed decrease in sperm quality may have been due to changes caused by infertility treatment or might reflect selection bias and not the reality of a true biological phenomenon
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