Temporal trends in sperm count : a systematic review and meta-regression analysis | Human Reproduction Update

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  • Sperm counts of Western men are plummeting, analysis finds - CNN.com
    http://edition.cnn.com/2017/07/25/health/sperm-counts-declining-study/index.html

    Sperm counts of men in North America, Europe, Australia and New Zealand are plunging, according to a new analysis published Tuesday.

    Among these men there has been a 52% decline in sperm concentration and a 59% decline in total sperm count over a nearly 40-year period ending in 2011, the analysis, published in the journal Human Reproduction Update, said.
    […]
    Though Levine emphasized that his analysis did not study the cause of declines, he speculated the reason may be “°we are exposed to many chemicals we’ve never been exposed to before.°”

    Previous studies, including his own, show that exposure in utero to endocrine disrupting chemicals can harm male reproductive system development and fertility potential. Commonly used chemicals, including pesticides, lead and fire retardants, can increase or decrease production of certain hormones within our bodies and so are said to disrupt our endocrine, or hormone-making, system.
    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.

    #perturbateur_endocrinien

    • Résumé de l’étude (accessible intégralement)

      Temporal trends in sperm count: a systematic review and meta-regression analysis | Human Reproduction Update | Oxford Academic
      https://academic.oup.com/humupd/article/doi/10.1093/humupd/dmx022/4035689/Temporal-trends-in-sperm-count-a-systematic-review

      Abstract

      BACKGROUND
      Reported declines in sperm counts remain controversial today and recent trends are unknown. A definitive meta-analysis is critical given the predictive value of sperm count for fertility, morbidity and mortality.

      OBJECTIVE AND RATIONALE
      To provide a systematic review and meta-regression analysis of recent trends in sperm counts as measured by sperm concentration (SC) and total sperm count (TSC), and their modification by fertility and geographic group.

      SEARCH METHODS
      PubMed/MEDLINE and EMBASE were searched for English language studies of human SC published in 1981–2013. Following a predefined protocol 7518 abstracts were screened and 2510 full articles reporting primary data on SC were reviewed. A total of 244 estimates of SC and TSC from 185 studies of 42 935 men who provided semen samples in 1973–2011 were extracted for meta-regression analysis, as well as information on years of sample collection and covariates [fertility group (‘Unselected by fertility’ versus ‘Fertile’), geographic group (‘Western’, including North America, Europe Australia and New Zealand versus ‘Other’, including South America, Asia and Africa), age, ejaculation abstinence time, semen collection method, method of measuring SC and semen volume, exclusion criteria and indicators of completeness of covariate data]. The slopes of SC and TSC were estimated as functions of sample collection year using both simple linear regression and weighted meta-regression models and the latter were adjusted for pre-determined covariates and modification by fertility and geographic group. Assumptions were examined using multiple sensitivity analyses and nonlinear models.

      OUTCOMES
      SC declined significantly between 1973 and 2011 (slope in unadjusted simple regression models −0.70 million/ml/year; 95% CI: −0.72 to −0.69; P < 0.001; slope in adjusted meta-regression models = −0.64; −1.06 to −0.22; P = 0.003). The slopes in the meta-regression model were modified by fertility (P for interaction = 0.064) and geographic group (P for interaction = 0.027). There was a significant decline in SC between 1973 and 2011 among Unselected Western (−1.38; −2.02 to −0.74; P < 0.001) and among Fertile Western (−0.68; −1.31 to −0.05; P = 0.033), while no significant trends were seen among Unselected Other and Fertile Other. Among Unselected Western studies, the mean SC declined, on average, 1.4% per year with an overall decline of 52.4% between 1973 and 2011. Trends for TSC and SC were similar, with a steep decline among Unselected Western (−5.33 million/year, −7.56 to −3.11; P < 0.001), corresponding to an average decline in mean TSC of 1.6% per year and overall decline of 59.3%. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. In a model restricted to data post-1995, the slope both for SC and TSC among Unselected Western was similar to that for the entire period (−2.06 million/ml, −3.38 to −0.74; P = 0.004 and −8.12 million, −13.73 to −2.51, P = 0.006, respectively).

      WIDER IMPLICATIONS
      This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by SC and TSC) between 1973 and 2011, driven by a 50–60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand. Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed.

    • ... his analysis did not study the cause of declines, he speculated ...

      Well, that moved quickly from evidence to speculation as to cause. So this is not a scientific journal but a space for speculation?