Sperm count drop 'could make humans extinct'
http://www.bbc.com/news/health-40719743
Researchers assessing the results of nearly 200 studies say sperm counts among men from North America, Europe, Australia, and New Zealand, seem to have halved in less than 40 years.
Some experts are sceptical of the Human Reproduction Update findings.
But lead researcher Dr Hagai Levine said he was "very worried" about what might happen in the future.
The assessment, one of the largest ever undertaken, brings together the results of 185 studies between 1973 and 2011.
Dr Levine, an epidemiologist, told the BBC that if the trend continued humans would become extinct.
Decline rate 'increasing'
"If we will not change the ways that we are living and the environment and the chemicals that we are exposed to, I am very worried about what will happen in the future," he said.
"Eventually we may have a problem, and with reproduction in general, and it may be the extinction of the human species."
Scientists not involved in the study have praised the quality of the research but say that it may be premature to come to such a conclusion.
Dr Levine, from the Hebrew University of Jerusalem, found a 52.4% decline in sperm concentration, and a 59.3% decline in total sperm count in men from North America, Europe, Australia and New Zealand.
The study also indicates the rate of decline among men living in these countries is continuing and possibly even increasing.
Previous research 'flawed'
In contrast, no significant decline was seen in South America, Asia and Africa, but the researchers point out that far fewer studies have been conducted on these continents. However, Dr Levine is concerned that eventually sperm counts could fall in these places too.
Many previous studies have indicated similar sharp declines in sperm count in developed economies, but sceptics say that a large proportion of them have been flawed.
Some have investigated a relatively small number of men, or included only men who attend fertility clinics and are, in any case, more likely to have low sperm counts.
There is also concern that studies that claim to show a decline in sperm counts are more likely to get published in scientific journals than those that do not. Another difficulty is that early methods of counting sperm may have overestimated the true count.
Taken together these factors may have created a false view of falling sperm counts.
But the researchers claim to have accounted for some of these deficiencies, leaving some doubters, such as Prof Allan Pacey of Sheffield University, less sceptical.
He said: "I've never been particularly convinced by the many studies published so far claiming that human sperm counts have declined in the recent past."
"However, the study today by Dr Levine and his colleagues deals head-on with many of the deficiencies of previous studies."
Smoking and obesity
But Prof Pacey believes that although the new study has reduced the possibility of errors it does not entirely remove them. So, he says, the results should be treated with caution.
"The debate has not yet been resolved and there is clearly much work still to be done.
"However, the paper does represent a step forward in the clarity of the data which might ultimately allow us to define better studies to examine this issue."
There is no clear evidence for the reason for this apparent decrease. But it has been linked with exposure to chemicals used in pesticides and plastics, obesity, smoking, stress, diet, and even watching too much TV.
Dr Levine says that there is an urgent need to find out why sperm counts are decreasing and to find ways of reversing the trend.
"We must take action - for example, better regulation of man-made chemicals - and we must continue our efforts on tackling smoking and obesity.
Study shows a significant ongoing decline in sperm counts of Western men
https://medicalxpress.com/news/2017-07-significant-ongoing-decline-sperm-western.html
Dr. Hagai Levine, the study's lead author and Head of the Environmental Health Track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine, in the Hebrew University's Faculty of Medicine. Credit: Hebrew University
In the first systematic review and meta-analysis of trends in sperm count, researchers from the Hebrew University-Hadassah Braun School of Public Health and Community Medicine and the Icahn School of Medicine at Mount Sinai report a significant decline in sperm concentration and total sperm count among men from Western countries. The study [under embargo until July 25 at 1 pm EDT] is published today in Human Reproduction Update, the leading journal in the fields of Reproductive Biology and Obstetrics & Gynecology.
By screening 7,500 studies and conducting a meta-regression analysis on 185 studies between 1973 and 2011, the researchers found a 52.4 percent decline in sperm concentration, and a 59.3 percent decline in total sperm count, among men from North America, Europe, Australia and New Zealand who were not selected based on their fertility status. In contrast, no significant decline was seen in South America, Asia and Africa, where far fewer studies have been conducted.
The study also indicates the rate of decline among Western men is not decreasing: the slope was steep and significant even when analysis was restricted to studies with sample collection between 1996 and 2011.
The research was led by Dr. Hagai Levine, Head of the Environmental Health Track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine, Jerusalem, with Dr. Shanna H Swan, Professor in the Department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai, New York, and an international team of researchers from Brazil, Denmark, Israel, Spain and the United States
While declines in sperm count have been reported since 1992, the question has remained controversial because of limitations in past studies. However, the current study uses a broader scope and rigorous meta-regression methods, conservatively addresses the reliability of study estimates, and controls for factors that might help explain the decline such as age, abstinence time, and selection of the study population.
"Given the importance of sperm counts for male fertility and human health, this study is an urgent wake-up call for researchers and health authorities around the world to investigate the causes of the sharp ongoing drop in sperm count, with the goal of prevention," said Dr. Hagai Levine, the lead author and Head of the Environmental Health Track at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine, in the Hebrew University of Jerusalem's Faculty of Medicine.
The findings have important public health implications. First, these data demonstrate that the proportion of men with sperm counts below the threshold for subfertility or infertility is increasing. Moreover, given the findings from recent studies that reduced sperm count is related to increased morbidity and mortality, the ongoing decline points to serious risks to male fertility and health.
"Decreasing sperm count has been of great concern since it was first reported twenty-five years ago. This definitive study shows, for the first time, that this decline is strong and continuing. The fact that the decline is seen in Western countries strongly suggests that chemicals in commerce are playing a causal role in this trend," Dr. Shanna H Swan, a professor in the Department of Environmental Medicine and Public Health at the Icahn School of Medicine at Mount Sinai, New York.
While the current study did not examine causes of the observed declines, sperm count has previously been plausibly associated with environmental and lifestyle influences, including prenatal chemical exposure, adult pesticide exposure, smoking, stress and obesity. Therefore, sperm count may sensitively reflect the impact of the modern environment on male health across the lifespan and serve as a "canary in the coal mine" signaling broader risks to male health.
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More information: Hagai Levine et al, Temporal trends in sperm count: a systematic review and meta-regression analysis, Human Reproduction Update (2017)