Something weird is going on with human sperm production. For decades, scientists have warned that sperm counts are dropping among Western men, but no one has really been able to prove it. In what is now the largest and most comprehensive study of its kind, scientists have presented compelling evidence in support of this rather alarming assertion, showing that sperm counts have dropped more than 50 percent in just four decades. 
 
 “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...” 
 
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 The sperm count decline is real and it’s not showing any signs of slowing down, according to new research published in Human Reproduction Update. By conducting a meta-analysis of 185 studies published between 1973 and 2011, researchers from the Hebrew University-Hadassah Braun School of Public Health and Community Medicine and the Icahn School of Medicine at Mount Sinai documented a 52.4 percent decline in sperm concentration, and a 59.3 percent decline in total sperm count among men living in North America, Europe, Australia, and New Zealand. The same declines were not observed among men living in South America, Asia, and Africa, where fewer studies have been performed. 
 
 Both total sperm counts and sperm concentration (i.e. the total number of sperm in a given volume) are good measures of male reproductive ability. The men used in these studies weren’t chosen because of any suspected fertility issues. Alarmingly, the rate of decline does not appear to be stopping; the downward slope was “steep and significant” even when the meta-analysis was restricted to studies done after 1995. 
 
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 “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 study lead author Hagai Levine in a statement. 
 
 
 
 Low sperm counts are often an indicator of other health problems, and are often used by doctors to predict health and morbidity. Reduced sperm is thought to be the result of environmental influences, including exposure to noxious chemicals while in the womb, exposure to pesticides, and lifestyle factors such as smoking, obesity, and stress. Not surprisingly, low sperm counts are also associated with reduced fertility. 
 
 Scientists began to notice that something was amiss with human sperm counts back in 1992, but the issue remained controversial due to unconvincing research. 
 
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 “Previous studies used smaller sample sizes, whereas our study was three times as large as [the one done back] in 1992,” explained Levine and his co-author Shanna H. Swan in an email to Gizmodo. “This enabled us to reliably measure and assess trends in subgroups.” 
 
 Other problems with the earlier research included poor or insufficient screening criteria, lack of quality control, and limited statistical methods—all of which were addressed in the new study, according to the researchers. 
 
 “We developed a very detailed protocol, all our selected studies were examined by two researchers independently, we had a strict quality control process, and we used state-of-the-art meta-regression methods not available in 1992,” said Levine and Swan. 
 
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 For the new analysis, the researchers pored through the existing body of research to evaluate the reliability of study estimates, and controls for factors that might explain the decline such as age, abstinence time, and selection of the study population. By doing so, the researchers were able to confirm what has been suspected for quite some time now. 
 
 “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,” said Swan. “The fact that the decline is seen in Western countries strongly suggests that chemicals in commerce are playing a causal role in this trend.” 
 
 But, that last part’s just speculation. Scientists don’t actually know what’s causing the sperm count crisis, but this study suggests the Western lifestyle may have something to do with it. Levine and Swan recommend that future analyses take a similar approach to their own and investigate parts of the world not covered in this latest analysis. 
 
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 “Studies should also look at environmental and lifestyle factors (such as chemical exposure, stress, and smoking), and semen quality,” Levine and Swan told Gizmodo. “Investments should also be made into studying male reproduction.” 
 
 And indeed, the impact of low sperm counts on male fertility should be of great concern. The researchers say the reported declines in sperm production have manifested in the general population, and that “more couples are infertile,” adding that “From statistical point of view, such a large decline must implicate [a] larger proportion of infertile and subfertile men.” 
 
 
 
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 We’re nowhere near a fertility crisis at the moment, so fears of us entering into a Handmaid’s Tale world are largely overstated. Sure, the data shows an ongoing downward trend, but that’s no guarantee it’ll continue into the future. For all we know we’ve hit (or will soon hit) a wall in terms of low sperm counts). But that has yet to be proven, and this research is admittedly scary. And for the growing number of couple who can’t conceive, this is already a serious problem. 
 
 [Human Reproduction Update] ||||| According to a new study, sperm counts in men from North America, Europe and Australia have dropped by more than 50 percent in less than 40 years. (Reuters) 
 
 The quality of sperm from men in North America, Europe and Australia has declined dramatically over the past 40 years, with a 52.4 percent drop in sperm concentration, according to a study published Tuesday. 
 
 The research — the largest and most comprehensive look at the topic, involving data from 185 studies and 42,000 men around the world between 1973 and 2011 — appears to confirm fears that male reproductive health may be declining. 
 
 The state of male fertility has been one of the most hotly debated subjects in medical science in recent years. While a number of previous studies found that sperm counts and quality have been falling, some dismissed or criticized the studies over factors such as the age of the men included, the size of the study, bias in counting systems or other aspects of the methodologies. 
 
 Some of the other concerns are outlined in an analysis published by the American Society of Andrology, which focuses on the male reproductive system. The skepticism also has to do with the difficulty of comparing records from a fertility center in the 1970s with one from today and with the fact a single man's sperm count may fluctuate during his life span due to his weight, use of alcohol and many other factors. 
 
 However, Shanna H. Swan, one of the authors of the new study published in the Human Reproduction Update, said that the new meta-analysis is so broad and comprehensive, involving all the relevant research published in English, that she hoped it would put some of the uncertainty to rest. Then the scientific community could move forward into putting its resources into figuring out the why of what is going on, she said. 
 
 “It shows the decline is strong and that the decline is continuing,” Swan said in an interview. 
 
 The analysis found drops only for men in Europe, North America and Australia and not for those in South America, Asia and Africa. Swan explained that this could mean that there's something specific to certain cultures or regions that affects sperm, but that it's also possible that there just isn't enough data yet to draw firm conclusions about the rest of the world. There have been far fewer sperm studies conducted in non-Western countries. (Some of the most recent ones have also noted a decline in aspects of sperm quality. A study published earlier this year about China's Hunan province found that 56 percent of sperm donations met the criteria for health in 2001 vs. only 18 percent in 2015.) 
 
 The most important data points in the new study involved sperm concentrations for what are known as “unselected” men who haven't yet proven they are fertile. These are men in the studies who are on the younger side and are not yet fathers or do not have partners who are pregnant. Researchers estimated that these men had an average sperm concentration of 99 million per milliliter in 1973 but that that had dropped to an average 47 million per milliliter in 2011. 
 
 That is a disturbing number given that, according to World Health Organization criteria, men with a sperm concentration of less than 40 million are considered to have an impaired chance of conceiving and those with a sperm concentration of less than 15 million per milliliter are unlikely to be able to have children. 
 
 These numbers mean “surprisingly higher proportions of men are falling into the infertile and sub fertile categories,” Swan said. 
 
 There are numerous theories about what may be happening to sperm. Many scientists say the most sensitive period may be during the first trimester, when the developing fetus's reproductive system may be impacted by a mother smoking, stress she experienced or food she ate. Exposure to chemicals that can change hormone levels, known as endocrine disrupters, are among the issues being studied. 
 
 Over the life span, men are also exposed to a number of other things that could potentially influence sperm concentration: pesticides, lead, X-rays, stress and countless other factors. 
 
 The changes in the womb can cause permanent damage, Swan explained, while the adult exposures are mostly reversible. 
 
 The issue of sperm isn’t just about having babies. 
 
 It has larger implications for men's health. Poor sperm health has been linked to cardiovascular issues, obesity, cancer and more generally to higher rates of hospitalization and death. While men’s life expectancy is increasing overall thanks to advances in medical care, nutrition and sanitation, it isn’t unthinkable that that could one day reverse. 
 
 “Having a low sperm count is a signal,” Swan said, “that there’s something wrong in men’s health overall.” 
 
 Read more: 
 
 The U.S. fertility rate just hit a historic low. Why some demographers are freaking out. 
 
 Not quite half of American teens have had sex by 18. That’s actually low. 
 
 Teen birthrate hits all-time low, led by 50 percent decline among Hispanics and blacks ||||| 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).
– The Western man's sperm count just isn't what it used to be. In what the Washington Post calls the largest and most comprehensive look into the matter, an international team of researchers reports in the journal Human Reproductive Update that after analyzing 185 previous studies involving 42,000 men worldwide between 1973 and 2011, they've observed a 52% drop in sperm concentration in men from North America, Europe, Australia, and New Zealand. This is in stark contrast to men in South America, Asia, and Africa, where no such decline was found, though not nearly as much data comes out of those regions, researchers report in press release. "Given the importance of sperm counts for male fertility and human health, this study is an urgent wake-up call," the lead author says. In 1973, the researchers estimate, men had an average sperm concentration of 99 million per milliliter. The World Health Organization puts the threshold for impaired chances of conception at 40 million, and today, the average Western male's sperm concentration has dropped very close to that: 47 million. And while there isn't exactly a fertility crisis among humans, Gizmodo calls the research "admittedly scary." Having a low sperm count has been linked to a range of increased health problems and even higher mortality. It's "a signal that there's something wrong in men's health overall," one researcher tells the Post, noting that "the decline is strong and ... the decline is continuing." What's causing the drop is up for debate, and everything from chemical and pesticide exposure to smoking and stress have been blamed. (Tight underwear could be part of the problem.)