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Recent research looked at environmental causes of male infertility, specifically endocrine-disrupting chemicals. Poor semen quality contributes to increases in infertility and the use of assisted reproductive technology.The researchers also discuss the higher incidence of testicular cancer worldwide, lower levels of testosterone in men, and poor semen quality among men aged 20 to 25 (with the average man having up to 90% abnormal sperm). From Science Daily:

Endocrine-disrupting chemicals may be threatening fertility in industrialized countries

The birth rate is declining in all industrialised countries, and socioeconomic factors and women's age are not solely to blame. Male reproductive health and environmental factors are also significant, as concluded in a new scientific review article. ...Behind the article are fertility researchers from Denmark, the US and Finland. The researchers studied a number of factors related to fertility, and one of the main conclusions of their study was that poor semen quality contributed to increases in infertility and the use of assisted reproductive technology.

The study also revealed higher incidence of testicular cancer worldwide, with the greatest frequency among Caucasian populations. Moreover, the researchers also observed lower levels of testosterone in average men. "I was surprised that we found such poor semen quality among young men aged 20 to 25. The average man had up to 90% of abnormal sperm. Normally, there would be so many sperms that a few abnormal ones would not affect fertility. However, it appears that we are at a tipping point in industrialised countries where poor semen quality is so widespread that we must suspect that it results in low pregnancy rates," said first author of the article, Professor Niels E. Skakkebaek from the Department of Growth and Reproduction (EDMaRC) at Rigshospitalet and the University of Copenhagen.

"The article also demonstrates the impact of the increasing number of male reproductive problems on low birth rates. There is no doubt that environmental factors are playing a role. These are the correlations we are researching at the new research centre EDMaRC at Rigshospitalet," added Professor Anders Juul, who is the last author of the article.

Many of the male reproductive problems could be due to damage to the testes during embryonic development. While the reproductive problems could arise from genetic changes, "recent evidence suggests that most often they are related to environmental exposures of the fetal testes," the researcher team wrote."Since the disorders in male genitals have increased over a relatively short period of time, genetics alone cannot explain this development. There is no doubt that environmental factors are playing a role and that endocrine-disrupting chemicals, which have the same effect on animals, are under great suspicion. The exposure that young people are subjected to today can determine not only their own, but also their children's, ability to procreate," explained Professor Skakkebaek.

A recent study found that men with infertility have a much higher risk for a variety of other chronic medical conditions, including diabetes, heart disease, renal disease, alcohol abuse, and drug abuse. Thus, it appears that male infertility may be a symptom or a clue that there may be other health problems. One example is that male infertility is linked to an 81% greater risk of diabetes, and the greatest risk for renal disease occurred among men with azoospermia (zero sperm counts, the most severe form of male infertility). From Medscape:

Infertility in Men Tied to Heart Disease, Chronic Conditions

Men with infertility have a higher risk for a variety of other chronic medical conditions, including diabetes, heart disease, alcohol abuse, and drug abuse, according to a retrospective cohort study published online December 7 in Fertility and Sterility."The results suggest that male factor infertility has more than just reproductive implications," write Michael Eisenberg, MD, assistant professor of urology and director of male reproductive medicine and surgery at Stanford University School of Medicine in California, and colleagues.

The researchers used insurance claims data from 2001 to 2008 from the Truven Health MarketScan to identify more than 115,000 patients for the study population. They compared outcomes among 13,027 men diagnosed with male factor infertility (average age, 33 years), with outcomes among 23,860 men (average age, 33 years) who received semen or infertility testing and with outcomes among 79,099 men who had received vasectomies.

The authors looked for 16 conditions: hypertension, diabetes, hyperlipidemia, renal disease, chronic pulmonary disease, liver disease, depression, peripheral vascular disease, cerebrovascular disease, ischemic heart disease, other heart disease, injury, alcohol abuse, drug abuse, anxiety disorders, and bipolar disorder.

The men with infertility had higher rates of obesity and smoking, but even after adjustment for these covariates and for age, follow-up time, and healthcare use, men with infertility had a higher risk for multiple conditions compared with vasectomized men or those receiving only fertility testing. Specifically, compared with the men who received fertility testing, men with infertility had a 30% increased risk for diabetes (hazard ratio [HR], 1.30; 95% confidence interval [CI], 1.10 - 1.53), a 48% increased risk for ischemic heart disease (HR, 1.48; 95% CI, 1.19 - 1.84) and for alcohol abuse (95% CI, 1.07 - 2.05), a 67% increased risk for drug abuse (HR, 1.67; 95% CI, 1.06 - 2.63), and a 19% increased risk for depression (HR, 1.19; 95% CI, 1.04 - 1.36).

Compared with men who received vasectomies, those with infertility had a 9% higher risk for hypertension (HR, 1.09; 95% CI, 1.02 - 1.17), a 14% greater risk for hyperlipidemia (HR, 1.14; 95% CI, 1.07 - 1.22), a 41% greater risk for ischemic heart disease (HR, 1.41; 95% CI, 1.19-1.67), and a 16% greater risk for other heart disease (HR, 1.16; 95% CI, 1.04 - 1.29). Further, men with infertility, compared with vasectomized men, had an 81% greater risk for diabetes (HR, 1.81; 95% CI, 1.57 - 2.08), a 60% greater risk for renal disease (HR, 1.60; 95% CI, 1.14 - 2.24), a 53% greater risk for liver disease (HR, 1.53; 95% CI, 1.31 - 1.80), and a 52% greater risk for peripheral vascular disorders (HR, 1.52; 95% CI, 1.12 - 2.07).

Yes, this finding is important , but what should be also noted is this sentence in the article: "He also noted that it may not be a disease itself, but the treatment for the disease, that's actually responsible for reproductive malfunction." It has been known for decades that men's sperm is affected by environmental chemicals (such as pesticides), alcohol, smoking, and medications. So it's important to figure out if it's the medicine or the health condition that's causing the problem - or perhaps it's both. From Science Daily:

Infertility is a warning: Poor semen quality linked to hypertension, other health problems

A study of men who were evaluated for the cause of their infertility finds previously unknown relationships between deficiencies in their semen and other, seemingly unrelated health problems. A study of more than 9,000 men with fertility problems has revealed a correlation between the number of different defects in a man's semen and the likelihood that the man has other health problems.

The study, conducted by investigators at the Stanford University School of Medicine, also links poor semen quality to a higher chance of having various specific health conditions, such as hypertension, and more generally to skin and endocrine disorders....A study Eisenberg co-authored a few years ago showed that infertile men had higher rates of overall mortality, as well as mortality linked to heart problems, in the years following an infertility evaluation. 

In the new study, Eisenberg and his colleagues analyzed the medical records of 9,387 men, mostly between 30 and 50 years old, who had been evaluated at Stanford Hospital & Clinics (now Stanford Health Care) between 1994 and 2011 to determine the cause of their infertility. ...So, using the database, the investigators were able to compare the overall health status of men who had semen defects to that of the men who didn't.

With a median age of 38, this was a fairly young group of men. However, 44 percent of all the men had some additional health problem besides the fertility problem that brought them to the clinic. In particular, the investigators found a substantial link between poor semen quality and specific diseases of the circulatory system, notably hypertension, vascular disease and heart disease. 

In addition, as the number of different kinds of defects in a man's semen rose, so did his likelihood of having a skin disease or endocrine disorder. When looking at the severity of all health problems, the scientists observed a statistically significant connection between the number of different ways in which a man's semen was deficient and the likelihood of his having a substantial health problem.... He also noted that it may not be a disease itself, but the treatment for the disease, that's actually responsible for reproductive malfunction. He said he is exploring this possibility now.

This article mentions a few of the other issues that are linked with male infertility.While incomplete, at least it mentions smoking, BPA exposure, binge drinking, obesity, and lack of sleep.From Medical Daily:

Your Sperm And Your Health: What Your Semen Can Tell You About Your Health

The following article focused on other links to male infertility. It also discussed an interesting 2012 study that looked at the effects of wearing tight briefs (which heats the genitals) versus boxers on sperm production (hint: briefs had very negative effect). From Five Thirty Eight Science:

Men, Those Tightie Whities Really Are Killing Your Sperm Count

Some recent research on sperm quality and implications for fertility. All from Science Daily:

Exposure to aluminum may impact on male fertility, research suggests

Research from scientists in the UK and France suggests that human exposure to aluminum may be a significant factor in falling sperm counts and reduced male fertility.Fluorescence microscopy using an aluminum-specific stain confirmed the presence of aluminum in semen and showed aluminum inside individual sperm.And the team of scientists, at the universities of Lyon and Saint-Etienne in France and Keele in the UK, found that the higher the aluminum, the lower sperm count.

Professor Exley said: "There has been a significant decline in male fertility, including sperm count, throughout the developed world over the past several decades and previous research has linked this to environmental factors such as endocrine disruptors"..."Human exposure to aluminum has increased significantly over the same time period and our observation of significant contamination of male semen by aluminum must implicate aluminum as a potential contributor to these changes in reproductive fertility."

Stress degrades sperm quality, study shows

Psychological stress is harmful to sperm and semen quality, affecting its concentration, appearance, and ability to fertilize an egg, according to a study. It is not fully understood how stress affects semen quality. It may trigger the release of steroid hormones called glucocorticoids, which in turn could blunt levels of testosterone and sperm production. Another possibility is oxidative stress, which has been shown to affect semen quality and fertility.

Twenty hours of TV a week linked to almost half sperm count of those who watch little TV

Healthy young men who watch TV for more than 20 hours a week have almost half the sperm count of men who watch very little TV, indicates a new study.

Cell phones negatively affect male fertility, new study suggests

Men who keep a cell phone in their pant pocket could be inadvertently damaging their chances of becoming a father, according to a new study. Previous research has suggested that radio-frequency electromagnetic radiation (RF-EMR) emitted by the devices can have a detrimental effect on male fertility. Most of the global adult population own mobile phones, and around 14% of couples in high and middle income countries have difficulty conceiving.

In control groups, 50-85% of sperm have normal movement. The researchers found this proportion fell by an average of 8 percentage points when there was exposure to mobile phones. Similar effects were seen for sperm viability. The effects on sperm concentration were less clear. 

Moderate weekly alcohol intake linked to poorer sperm quality in healthy young men

Moderate alcohol intake of at least 5 units every week is linked to poorer sperm quality in otherwise healthy young men, suggests research. And the higher the weekly tally of units, the worse the sperm quality seems to be, the findings indicate, prompting the researchers to suggest that young men should be advised to steer clear of habitual drinking.

Sperm size, shape in young men affected by cannabis use

Young men who use cannabis may be putting their fertility at risk by inadvertently affecting the size and shape of their sperm, according to new research. In the world's largest study to investigate how common lifestyle factors influence the size and shape of sperm, a research team found that sperm size and shape was worse in samples ejaculated in the summer months, but was better in men who had abstained from sexual activity for more than six days.

Researchers found that many common chemicals, including Triclosan, interfere with normal sperm function. Perhaps this is contributing to fertility problems.From Science Daily:

Endocrine disruptors impair human sperm function, research finds

A plethora of endocrine-disrupting chemicals interfere with human sperm function in a way that may have a negative impact on fertilization. These are the findings of a German -- Danish team of researchers from the Center of Advanced European Studies and Research in Bonn, Germany, and the University Department of Growth and Reproduction, Rigshospitalet, Copenhagen, Denmark. The work, which is published in EMBO reports,suggests that endocrine disruptors may contribute to widespread fertility problems in the Western world in a way that hitherto has not been recognized.

Endocrine disruptors are present in food, textiles, drugs, household, and personal-care products such as plastic bottles, toys, and cosmetics. Proving the deleterious effects of endocrine disruptors on human beings has been difficult due to a lack of suitable experimental systems.

"For the first time, we have shown a direct link between exposure to endocrine disrupting chemicals from industrial products and adverse effects on human sperm function,'' said Niels E. Skakkebaek, professor and leader of the Danish team.

Hundreds to thousands of chemicals can be rapidly tested for their potential to interfere with human sperm function using the bioassay developed by the researchers. In this initial study, about one hundred chemicals were tested. Around one third, including ultraviolet (UV) filters like 4-methylbenzylidene camphor (4-MBC) used in some sunscreens, the anti-bacterial agent Triclosan used in toothpaste, and di-n-butylphthalate (DnBP), showed adverse actions.

Altogether, the study indicates that endocrine disruptors might disturb the precisely coordinated sequence of events underlying fertilization in several ways: the chemicals might evoke changes in swimming behaviour at the wrong time and wrong place, hinder navigation of sperm towards the egg, and hamper penetration into the protective egg coat.

Different article about the same research, and here they also discuss the very important finding that mixtures of common chemicals have an even stronger adverse "cocktail effect" on sperm. From The Independent:

Chemicals in soap can cause male infertility, claim scientists

They also found that the concentrations needed to trigger these adverse reactions were similar to the very low levels commonly found within the human body. In addition, they showed for the first time that there was a “cocktail effect”, when a number of chemicals worked together to amplify their individual effects.