Sperm count in men from North America, Europe, Australia and New Zealand declined by 50-60% between 1973 and 2011, according to a new study from the Hebrew University of Jerusalem. Surprisingly, the study, which analyzed data on the sperm counts of 42 935 men, found no decline in sperm counts in men from Asia, Africa and South America, although there was limited data from these areas.
Overall, this is a very disturbing report. There has been a longstanding debate among scientists as to whether sperm counts have decreased or not. But what’s different about this study is the quality of the analysis. It was done in a systematic manner, accounting for several of the problems that had affected previous studies, such as the method used to count sperm and comparing studies performed sometimes decades apart. As such, most experts agree that the data presented is of a high quality and that the conclusions, although alarming, are reliable.
So what is going on? There has been a concern for a number of years about an increase in abnormalities in male reproductive health, such as testicular cancer. The decline in sperm counts is consistent with these increases and this adds weight to the concept that male reproductive health is under attack and is declining rapidly.
In fact, if the data on sperm counts is extrapolated to its logical conclusion, men will have little or no reproductive capacity from 2060 onwards. The most rational explanation for the decline in male reproductive health is the changes in the environment. Current research suggests that the male foetus is particularly susceptible to exposure to pollutants and so changes that occur early in foetal life can have a very significant effect on the adult.
What can be done?
The simple answer is that we need much more research to find out why this decline in sperm count is happening. We cannot be complacent about the potential negative effect on fertility and must now urgently rally to substantially increase the research effort into male reproductive health.
Also, although the prevailing evidence shows a decline in reproductive health, not all studies show this; there are some geographical differences. It will be critical to determine what the key differences between geographical regions are – such as genetic differences and exposure to specific pollutants – so we can then examine treatment strategies to limit these negative effects.
If it’s the foetus that is mainly affected, what can the adult man do? Even in adults, exposure to chemicals, such as bisphenol A, which are thought to affect fertility, can have a negative effect, so men should limit their exposure to toxic chemicals. This includes stopping cigarette smoking. Also, a healthy lifestyle is very important as there is a known link between obesity and reduced sperm count.
Written by Chris Barratt, Professor of Reproductive Medicine, University of Dundee (The Conversation)
Chris Barratt receives funding from MRC NHS and Bill and Melinda Gates Foundation Editor In Chief MHR
"Temporal trends in sperm count: a systematic review and meta-regression analysis" – Hagai Levine et al. – Oxford Academic, Human Reproduction Update – July 25, 2017 – DOI: https://doi.org/10.1093/humupd/dmx022 – OPEN ACCESS
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.
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.
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).
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.
Featured image credit: NASA
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