EXPERT REACTION: Study of studies points to falling sperm counts in western men

Embargoed until: Publicly released:

A steady decline in sperm count over the last 40 years among men in Australia, New Zealand, Europe and North America is reported by international scientists reviewing 185 separate studies. Although previous studies reporting sperm declines have been controversial due to the quality of the data, the researchers say that, after quality control measures, they still found a 50 per cent overall reduction in sperm concentration. They suggest that future research should focus on identifying lifestyle factors behind falling sperm counts. Australian experts respond below.

Journal/conference: Human Reproduction Update

Link to research (DOI): 10.1093/humupd/dmx022

Organisation/s: Hebrew University of Jerusalem, Israel

Funder: Environment and Health Fund (EHF), Jerusalem, Israel; American Healthcare Professionals and Friends for Medicine in Israel (APF); Israel Medical Association (IMA); Research Fund of Rigshospitalet (Grant no. R42-A1326); The Brazilian National Council for Scientific and Technological Development (CNPq 249184/2013-3); The Mount Sinai Transdisciplinary Center on Early Environmental Exposures.

Media Release

From: The Hebrew University of Jerusalem

Comprehensive study shows a significant ongoing decline in sperm counts of Western men

Meta-analysis finds that among men from North America, Europe and Australia, sperm concentration has declined more than 50 percent in less than 40 years, pointing to impaired male health and decreasing fertility

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.

Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr Orly Lacham-Kaplan is Senior Scientist in the Centre for Exercise & Nutrition at Australian Catholic University

The data presented is indeed a true representation of the situation with sperm count and concentration. There is a decline in sperm count and concentration up to 60 per cent over four decades. Although it will be interesting to identify the causes associated with this directly (which will be based on large scale epidemiological studies), as a reproductive biologist it will be more interesting to see data associated with semen quality. Although there are many studies that show correlation between sperm count concentration and quality, the information would have been helpful.

Also, a follow up study including the same individuals over a span of several years would be interesting. There is information to associate all cause morbidity with sperm count and concentration and this is something to think about; i.e. is sperm count and concentration is indicative of poor health?
As for Australia, I would not worry our 'guys' too much, just to maybe be a bit conscious. I will refer to the study as informative rather than scientific and maybe, just maybe the simple(r) life in non-western countries is actually the best, even for sperm.  Maybe a study can be done in Australia regarding city men versus rural men?

Last updated: 25 Jul 2017 3:32pm
Dr Shaun Roman is the Assistant Dean, International & Marketing and Program Convenor for the Bachelor of Biotechnology in the Faculty of Science and Information Technology and Head of Biology in the School of Environmental and Life Sciences at the University of Newcastle.

On face value this study suggests a decline in sperm numbers continues. These numbers follow the numbers of the other studies cited.

The dates used in the study were the date of sampling and are not related to the age of the donor. So there is not an age effect but an environmental effect that is limited to 'western countries'. This requires some vigorous investigation.

However it should be noted that it only takes one sperm to fertilise an egg and, on average, western men are still producing 50 million per ejaculate. We are not in crisis yet but this study serves as a warning that we should investigate the role our diet and environment pay on sperm production.

Last updated: 25 Jul 2017 2:02pm
Professor Kelton Tremellen is Professor of Reproductive Medicine at Flinders University

This paper confirms previously observations of a significant fall in sperm counts over the last four decades. However, what is interesting about this latest analysis is that it the decline in sperm counts appears to primarily effect men from western countries like Australia and United States, not those from Africa or Asia. This suggests an environmental or lifestyle issue specific to western society is the underlying cause.

The most likely cause of this halving of sperm count is obesity. Poor diet and lack of exercise, both endemic in the western world, has resulted in two-thirds of men being overweight or obese, and obesity is known to be a significant risk factor for both low testosterone levels and sperm count.

Men should take these results as a wake-up call to adopt a healthy lifestyle. By maintaining a healthy weight, plus eating plenty of good foods like fish, nuts, fresh fruit and vegetables, while avoiding high fat and sugar foods, will help maintain both a healthy sperm count and good overall health.

Last updated: 25 Jul 2017 2:00pm
Professor Rob McLachlan is Director of Clinical Research at the Hudson Institute of Medical Research and Director of Andrology Australia

The paper by Levine et al is at first glance alarming in reporting a 50 per cent decline in sperm output across the world over the past forty years.  While not providing new primary data, it provides a meta-analysis of the hundreds of papers that have examined the semen quality over many years.
Examining for trends in semen quality is extremely challenging as one needs to find a way of assessing whole populations (not just selected men) using consistent analytical procedures over decades. If it were an easy issue to pin down, it would have been done years ago. This issue has been controversial, as issues of patient selection and inconsistent methodologies have resulted in varying conclusions.  For example, a paper describing 4867 young Danish men showed a modest increase in sperm counts between 1996 and 2010.  Other studies have shown no change, while others have also suggested decline. 
The current paper represents a concerted effort to collate and evaluate 185 studies involving 43,000 men over 38 years in the hope that the statistical power derived from so many studies will compensate for potential flaws in the component studies.  The authors excluded many studies because they had overtly biased patient samples. Those that were evaluated were classed as involving either ‘unscreened men’ who were considered to have no reason to be concerned about their fertility and therefore might be potentially representative of general population. Others were classed as ‘fertile’ due to their proven fertility.  A decline was reported in both groups. There were differences in geographical regions; only the western centres showing a decline.
It is unlikely that anything more can be done in the foreseeable future to definitively answer this major public health question. But taking a cautionary path, this latest analysis presents the challenge to identify and address potential negative impactors on male fertility such as lifestyle, obesity and comorbidities that are rising in developed countries particularly, and generally the role of environmental toxicants for which there is certainly evidence in more select populations. 
Ultimately the concern is that a fall in sperm output will be reflected in delays in natural conception rates. To date this has not been established. There is much more awareness and discussion of fertility, and major changes in the management of male infertility over the past 25 years in particular. Between 4-7 per cent of western populations are now conceived using assisted reproductive technology (ART).  Male factor infertility accounts solely or in part for half of ART treatment. An apparent increase in male infertility may reflect the success of sperm microinjection technology with more male factor couples coming to recognition.
This meta-analysis will no doubt increase the debate about health and environmental impacts on male reproductive health.

Last updated: 25 Jul 2017 1:57pm

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