Sperm counts have declined by nearly 60 per cent in just 40 years among men living in the Western countries, according to a major review of scientific studies published in the journal Human Reproduction.The researchers found no significant declines in the sperm counts and sperm concentrations of men living in South America, Asia and Africa.
According to a research, there has been a 52 per cent decline in sperm concentration and a 59 per cent decline in total sperm count over a nearly 40-year period ending in 2011 in Europe, North America, Australia and New Zealand.
According to the research, pesticides, hormone-disrupting chemicals, diet, stress, smoking and obesity have all been plausible associated with the problem, which is associated with a range of other illnesses such as testicular cancer and a generally increased mortality rate.“Therefore, sperm count may sensitively reflect the impacts of the modern environment on male health throughout the life course.”
Chemicals linked to lowering sperm count include some used to make plastics more flexible and flame retardants used in furniture. These can enter the food chain after they are taken in by plants or eaten by animals.
A diet high in alcohol, caffeine, processed meat, soy and potatoes may also have an adverse effect on male fertility.
According to a research published in the journal Human Reproduction, there has been a 52 per cent decline in sperm concentration and a 59 per cent decline in total sperm count over a nearly 40-year period ending in 2011.
Researchers led by Dr Hagai Levine of Hebrew University of Jerusalem examined thousands of studies and then conducted a meta-analysis of 185 studies. These included 42,935 male participants who provided semen samples between 1973 and 2011. The chosen studies were well distributed over the nearly 40 years of the study period and among 50 different countries.
The analysis included information on fertility status, age, ejaculation abstinence time, semen collection method, sperm count method and geographic location at the level of Continent.
In a study, scientists determine sperm count by looking at a sample of ejaculate under a microscope.For sperm concentration, they measure how many millions of sperm there are in each millilitre of fluid.
"The extent of the decline is a heartache," said Levine.-- it's hard to believe for me."
The high proportion of men in Western countries with sperm concentrations below 40 million/ml is "particularly concerning," wrote Levine and his co-researchers, because evidence indicates that a sperm concentration below this threshold is associated with a "decreased monthly probability of conception."
Many people did not accept the results of the study, said Levine, it was quite controversial whether or not there is a decline." However, Levine noted, "there were serious limitations to the Carlsen study published in 1992." For example, a common criticism of the Carlsen group is that it included one overly large study -- it contributed 30% of the total participants, thus heavily influenced the results. By comparison, the largest of the studies examined by Levine's group included only 5% of all participants.
Since 1992, other researchers conducted analyses to understand whether sperm counts have declined, yet the results were mixed.
"Now we have a pretty solid answer," said Levine, who said his own study performed a meta-regression, "a more conservative, sophisticated analysis," one that accounts for factors that might influence the results.
Sonya Lunder, a senior analyst at the nonprofit advocacy group Environmental Working Group, noted that sperm is manufactured daily by men's bodies. Recent exposures to environmental chemicals would have an effect on sperm, which serves as a good indicator of contamination, while also serving as a good biomarker of men's health.
Lunder cites the work of Russ Hauser, a professor of reproductive physiology at Harvard T.H. Chan School of Public Health, who suggests that exposure to endocrine-disrupting chemicals may be associated with poorer sperm quality among men and worse reproductive outcomes among women.