Background: The global decline of human sperm quality remains a matter of debate.  Although many prior studies were flawed (more), numerous studies from the international literature describe a global decrease in sperm concentration among men.  A recent study from France looked at 26,000 normal men (ages 18 to 70, with infertile female partners) and identified a significant and continuous decrease in sperm concentration and in normal-shaped sperm between 1989 and 2005.

Some studies have shown that mean sperm counts have decreased significantly since the 1940’s.  The current trend for decline in semen parameters parallels increasing levels of obesity worldwide.  However, there is great geographic and ethnic variation.

Recent research from April 2015 again indicates that during the past 30 years, a decline in semen quality was found in semen parameters analyzed in Spanish men with proven fertility.  See the study here in Journal of Urology.

Semen quality may be the most sensitive marker of adverse environmental exposures, and a particular decline has been noted in many countries including Finland.

Bottom line: The most recent sperm concentration values in Spanish and French men could be linked to an unknown environmental cause (for example, pesticides or components of plastic).  Additional studies will be needed to determine if this decline is occurring in all nations, the causes, and whether the decline will continue.

There are many difficult-to-control confounding factors in the highly variable nature of semen, and comparability of populations from different time periods in secular-trend studies, the quality of laboratory methods for counting sperm, and geographic variations in semen quality.  All of these complicate the interpretation of the available evidence.   More high quality studies are needed to definitively identify semen quality trends throughout the world.