In 1992 Carlsen and coworkers published a controversial meta study claiming, that there had been a decline in mean sperm count from 113 million per ml in 1940 to 66 million per ml in 1990 and in seminal volume from 3.40 ml to 2.75 ml (p = 0.027), indicating an even more pronounced decrease in sperm production than expressed by the decline in sperm density. (Carlsen E, Giwercman A, Keiding N, Skakkebaek NE. Evidence for decreasing quality of semen during past 50 years. Br Med J 1992; 305: 609–613.)
The part of all men with sperm density > 100 million/mL fell from 50 % to 16 % in fifty years’ time, as seen in the figure:
A newly published international study by Levine and coworkers applying meta-regression analysis of 185 single studies confirmed that male sperm count had declined significantly in the Western World. (Levine H, Jørgensen N, M-A Anderson, Mendiola J, Weksler-Derri D, Mindlis I, Pinotti R, Swan SH Temporal trends in sperm count: a systematic review and meta-regression analysis. Human Reproduction Update 2017: 1–14.)
The authors found that sperm concentration among western men, unaware of their fertility, fell from 99 million per ml in 1973 to 47.1 million per ml in 2011 – a decline of 52.4 %.
Sperm count is predictive for fertility, morbidity and mortality, and sperm count may sensitively reflect the impacts of the modern environment on male health throughout the life course.
The outlook is alarming, humans will have more and more difficulties in reproducing themselves, if this tendency continues. The changing factors in our life causing this kind of impact have to be controlled!
Is the cause exposures to chemicals in medicine, vaccine, foods, cosmetics, pesticides, tobacco smoke, drugs, drinking water, beverage, consumer products, surfactants, textiles, toys, polluted air indoors and outdoors, work exposures, vitamin deficiencies etc.? or some combinations?
In Denmark we have more of the World top 10 scientists in this field, and we know some of the factors behind the decreasing semen quality and increasing testis cancer. However, regulation and control is difficult to implement as long the impact on fertility is not considered specially serious and urgent by decision makers.