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Comprehensive study shows a significant ongoing decline in sperm counts of Western men, pointing to impaired male health and decreasing fertility

25/07/2017

Meta-analysis finds that among men from North America, Europe and Australia, sperm concentration has declined more than 50% in less than 40 years

SUMMARY: A rigorous and comprehensive meta-analysis of data collected between 1973 and 2011 finds that among men from Western countries who were not selected on the basis of their fertility status, sperm concentration declined by more than 50%, with no evidence of a “leveling off” in recent years. These findings strongly suggest a significant decline in male reproductive health that has serious implications beyond fertility and reproduction, given recent evidence linking poor semen quality with higher risk of hospitalization and death. Research on causes of this ongoing decline and their prevention is urgently needed.

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.

[Video available at https://youtu.be/rb98liTzSgA]

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.

The Hebrew University-Hadassah Braun School of Public Health and Community Medicine is the first school of public health in Israel and one of five schools within the Hebrew University’s Faculty of Medicine. Since 1961, both in Israel and internationally, the Braun School, which is APHEA accredited, has improved the physical, mental and social well-being of populations, trained a public health workforce for the challenges of today and the future, conducted public health research, and made an impact on health services and policy. The School’s renowned International Master’s in Public Health (IMPH) program prepares graduates to take up key positions as leaders and teachers of public health in their home countries.

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Researchers who participated in this study are affiliated with Hebrew University-Hadassah Braun School of Public Health and Community Medicine, and the Hebrew University Center of Excellence in Agriculture and Environmental Health, Jerusalem, Israel; Department of Environmental Medicine and Public Health, and Gustave L. and Janet W. Levy Library, Icahn School of Medicine at Mount Sinai, New York, NY, USA; University Department of Growth and Reproduction,  University of Copenhagen, Rigshospitalet, Copenhagen, Denmark; Department of Physiology, Federal University of Parana, Curitiba, Brazil; Division of Preventive Medicine and Public Health, University of Murcia School of Medicine and Biomedical Research Institute of Murcia, Murcia, Spain; Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel.

Photo for download: http://media.huji.ac.il/new/photos/hu170725_sc1.JPG - 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. (Photo credit: Hebrew University)

Video for download: http://media.huji.ac.il/new/photos/hu170725_sc2.mp4 - Have Sperm Counts Declined? Definitely Yes, Says First-Ever Meta-Analysis on Trends in Sperm Count (Video credit: Hebrew University)

CITATION: Temporal trends in sperm count: A systematic review and meta-regression analysis. Hagai Levine, Niels Jørgensen, Anderson Martino‐Andrade, Jaime Mendiola, Dan Weksler-Derri, Irina Mindlis, Rachel Pinotti, Shanna H Swan. Human Reproduction Update, July 25, 2017, doi:10.1093/humupd/dmx022. Link: https://academic.oup.com/DocumentLibrary/humupd/PR/dmx022_final.pdf.

FUNDING: Researchers received support from the Environment and Health Fund (EHF), Jerusalem, Israel; American Healthcare Professionals and Friends for Medicine in Israel (APF); Israel Medical Association (IMA) [Levine]; Research Fund of Rigshospitalet (grant no. R42-A1326) [Jørgensen); The Brazilian National Council for Scientific and Technological Development [Martino-Andrade]; The Mount Sinai Transdisciplinary Center on Early Environmental Exposures (NIH P30ES023515) [Swan]. 

Comprehensive study shows a significant ongoing decline in sperm counts of Western men, pointing to impaired male health and decreasing fertility
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Higher BMI in Adolescence May Affect Cognitive Function in Midlife

11/12/2016

Study of Israeli adolescents also looks at impact of socioeconomic position on subsequent cognitive impairment

Overweight and obesity in adolescents have increased substantially in recent decades, and today affect a third of the adolescent population in some developed countries. While the dangers posed by high adult BMI on cognitive function in later life have been documented, the association of adolescent BMI with cognitive function in midlife has not yet been reported. (BMI, or Body Mass Index, is a calculation of a person’s weight in kilograms divided by the square of their height in meters.)

To shed light on this issue, scientists at the Hebrew University-Hadassah Braun School of Public Health and Community Medicine set out to determine the association between cumulative life course burden of high-ranked body mass index (BMI), and cognitive function in midlife. The research, which will appear in the Journal of Alzheimer’s Disease 55(3), was led by Prof. Jeremy Kark from the Braun School, in the Hebrew University of Jerusalem’s Faculty of Medicine, working with colleagues in Israel and the United States.

The researchers used weight and height data from 507 individuals tracked from over 33 years starting at age 17. The participants completed a computerized cognitive assessment at ages 48–52, and their socioeconomic position was assessed by multiple methods. Using mixed models the researchers calculated the life-course burden of BMI from age 17 to midlife, and used multiple regression to assess associations of BMI and height with global cognition and its five component domains.

In this population-based study of a Jerusalem cohort, followed longitudinally from adolescence for over 33 years, we found that higher BMI in late adolescence and the long-term cumulative burden of BMI predicted poorer cognitive function later in life. Importantly, this study shows that an impact of obesity on cognitive function in midlife may already begin in adolescence, independently of changes in BMI over the adult life course,” said the paper’s senior author, Prof.  Jeremy Kark of the Hebrew University-Hadassah Braun School of Public Health and Community Medicine.

“Our results also show that taller stature was associated with better global cognitive function, independent of childhood and adult socioeconomic position, and that height increase in late adolescence, reflecting late growth, conferred a protective effect, but among women only,” added Irit Cohen-Manheim, doctoral candidate at the Braun School and lead author.

The researchers point out that while socioeconomic position may have a particularly important role in the trajectory of a person’s lifetime cognitive function, it has rarely been adequately taken into account: “To the best of our knowledge, the association between BMI and cognition as a function of childhood and adult socioeconomic position has not been previously reported. Childhood household socioeconomic position appears to strongly modify the association between adolescent BMI and poorer cognition in midlife, the inverse association being restricted to low childhood socioeconomic position,” said Prof. Kark.

"Our results are consistent with the hypothesis that childhood living conditions, as reflected also by height, influence cognitive function later in life; however, our study is unique in showing that an adverse association of higher BMI with cognitive function appears to begin in adolescence and that it appears to be restricted to adults with lower childhood socioeconomic position,” said Prof.  Kark.

Evidence for the association between impaired cognitive function in midlife and subsequent dementia supports the clinical relevance of our results. Findings of the relation of BMI in adolescence with poorer midlife cognitive status, particularly in light of the ongoing epidemic of childhood obesity, require confirmation," said Irit Cohen-Manheim.

Scientists involved in this research are affiliated with the Hebrew University-Hadassah Braun School of Public Health and Community Medicine, Jerusalem, Israel; Department of Clinical Research, NeuroTrax Corporation, Modiin, Israel; Centre for Medical Decision Making, Ono Academic College, Kiryat Ono, Israel; Department of Neurology, Albert Einstein College of Medicine, Bronx, NY, USA; Biostatistics Unit, Gertner Institute for Epidemiology and Health Policy Research, Tel-Hashomer, Israel.

FUNDING: The research was supported by grants from the Chief Scientist of the Israel Ministry of Health, the Israel Science Foundation, and the US-Israel Binational Science Foundation to Prof. Jeremy Kark.

REFERENCE: Irit Cohen-Manheim, Glen M. Doniger, Ronit Sinnreich, Ely S. Simon, Havi Murad, Ronit Pinchas-Mizrachi and Jeremy D. Kark. Body Mass Index, Height, and Socioeconomic Position in Adolescence, Their Trajectories into Adulthood, and Cognitive Function in Midlife. The Journal of Alzheimer's Disease 55(3), article pre-published on December 6, 2016, DOI: 10.3233/JAD-160843.

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

Higher BMI in Adolescence May Affect Cognitive Function in Midlife
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Increased BMI During Adolescence Predicts Fatal Cardiovascular Events In Adulthood

14/04/2016
Nationwide study of 2.3 million Israeli adolescents examined from 1967 through 2010 finds association between elevated BMI in late adolescence and subsequent cardiovascular mortality in midlife

Overweight and obesity in adolescents have increased substantially in recent decades, and currently affect a third of the adolescent population in some developed countries. This is an important public health concern because obesity early in life is considered to be a risk factor for death from cardiovascular disease and from all causes in adulthood.

Some studies suggest that an elevated body-mass index is associated with an increased risk of death from cardiovascular causes. However, a determination of the BMI threshold that is associated with increased risk of fatality remains uncertain. (BMI is a calculation of a person’s weight in kilograms divided by the square of their height in meters, to quantify body mass and enable categorization as underweight, normal weight, overweight, or obese.)

In light of the worldwide increase in childhood obesity, Prof. Jeremy Kark from the Hebrew University-Hadassah Braun School of Public Health and Community Medicine, in the Hebrew University of Jerusalem’s Faculty of Medicine, together with Dr. Gilad Twig of Sheba Medical Center, and Dr. Hagai Levine also of the Braun School of Public Health and other colleagues in Israel, set out to determine the association between body-mass index (BMI) in late adolescence and death from cardiovascular causes in adulthood.

Their study, which appears in The New England Journal of Medicine, was based on a national database of 2.3 million Israeli 17 year olds in whom height and weight were measured between 1967 and 2010. The researchers assessed the association between BMI in late adolescence and death from coronary heart disease, stroke, and sudden death in adulthood by mid-2011.

During 42,297,007 person-years of follow-up, 2918 of 32,127 deaths (9.1%) were from cardiovascular causes, including 1497 from coronary heart disease, 528 from stroke, and 893 from sudden death.

The results showed an increase in the risk of cardiovascular death in the group that was considered within the “accepted normal” range of BMI, in the 50th to 74th percentiles, and of death from coronary heart disease at BMI values above 20. The researchers concluded that even BMI considered “normal” during adolescence was associated with a graded increase in cardiovascular and all-cause mortality during the 40 years of follow-up. This included increased rates of death from coronary heart disease, stroke, and total cardiovascular causes among participants.

As BMI scores increased into the 75th to 84th percentiles, adolescent obesity was associated with elevated risk of death from coronary heart disease, stroke, sudden death from unknown causes, and death from total cardiovascular causes, as well as death from non-cardiovascular causes and death from all causes. Participants also had an increased risk of sudden death.

The rates of death per person-year were generally lowest in the group that had BMI values during adolescence in the 25th to 49th percentiles, although higher rates were observed among those below the 5th percentile.

How might adolescent BMI influence cardiovascular outcomes in adulthood? The researchers considered two possible pathways. First, obesity may be harmful during adolescence, since it has been associated with unfavorable metabolic abnormalities through risk factors such as unfavorable plasma lipid or lipoprotein levels, increased blood pressure, impaired glucose metabolism, insulin resistance, and formation of coronary and aortic atherosclerotic plaques. Furthermore, the timing of exposure to obesity during a person's lifetime may play an important role. Second, BMI tends to "track' along the life course so that overweight adolescents tend to become overweight or obese adults, and overweight or obesity in adulthood affects the risk of cardiovascular disease.

“Our findings appear to provide a link between the trends in adolescent overweight during the past decades and coronary mortality in midlife,” said the paper’s senior author, Prof.  Jeremy Kark of the Hebrew University-Hadassah Braun School of Public Health and Community Medicine. “The continuing increase in adolescent BMI, and the rising prevalence of overweight and obesity among adolescents, may account for a substantial and growing future burden of cardiovascular disease, particularly coronary heart disease.”

Scientists involved in this research are affiliated with the Department of Medicine and the Dr. Pinchas Bornstein Talpiot Medical Leadership Program, Sheba Medical Center; Israel Defense Forces Medical Corps; Sackler School of Medicine, Tel Aviv University; Hebrew University-Hadassah Braun School of Public Health and Community Medicine; Israel Ministry of Health; Department of Medicine, Mount Auburn Hospital; and Harvard Medical School.

FUNDING: The study was funded by a research grant from the Environment and Health Fund in Jerusalem

REFERENCE: Gilad Twig, Gal Yaniv, Hagai Levine, Adi Leiba, Nehama Goldberger, Estela Derazne, Dana Ben‑Ami Shor, Dorit Tzur, Arnon Afek, Ari Shamiss, Ziona Haklai, and Jeremy D. Kark. Body-Mass Index in 2.3 Million Adolescents and Cardiovascular Death in Adulthood. The New England Journal of Medicine, published on April 13, 2016, at NEJM.org. DOI: 10.1056/NEJMoa1503840. LINK: http://www.nejm.org/doi/full/10.1056/NEJMoa1503840

The Hebrew University of Jerusalem is Israel’s leading academic and research institution, producing one-third of all civilian research in Israel. For more information, visit http://new.huji.ac.il/en.

Increased BMI During Adolescence Predicts Fatal Cardiovascular Events In Adulthood
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