Tag Archives: fertility

Long Term Effects on Sperm Count, Fertility from Pesticides

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Sounding the Alarm on Connection Between Fertility and Pesticide Exposure

A systematic review of scientific studies on pesticides and fertility finds exposure associated with lower semen quality, DNA fragmentation and chromosomal abnormalities.

A systematic review of scientific studies on pesticides and fertility finds exposure associated with lower semen quality, DNA fragmentation and chromosomal abnormalities.

Published in the journal Andrology, the review is yet another warning from a long string of researchers sounding the alarm over the connection between global fertility and toxic chemical exposure.

With data from the Centers for Disease Control and Prevention (CDC) indicating roughly one in five couples are unable to conceive after a year of trying, and trends continuing to slope downwards, it is critical that contributing factors be identified so that protective changes can be made.

After screening more than 1,300 studies, researchers narrowed their review down to 64 papers assessing semen parameters and DNA integrity after pesticide exposure. Each study is analyzed for its design, the pesticide investigated, the population studied, controls and reproductive effects determined.

Pesticides are evaluated for their impacts to sperm quality and DNA integrity based on their chemical class. Organochlorine insecticides, which are all banned but still persistent in soil, air, water and food in the United States, include a range of impacts to sperm quality.

Higher levels of DDT or its breakdown metabolite DDE are associated with lower semen count, and motility and morphology below normal threshold values established by the World Health Organization (WHO). (Under WHO threshold values, a sub-fertile condition is defined by values lower than the fifth percentile of the general population.)

Several studies find that as organochlorine concentrations increase in individual males, sperm parameters also fall.

In addition to sperm quality, organochlorines are associated with chromosomal aberrations in several studies, including effects such as sperm disomy, where sperm have extra or missing chromosomes. This can result in viable offspring, but those offspring are at greater risk of abnormalities.

Organophosphate, the class of insecticides that replaced the organochlorines as they were phased out, also present a range of deleterious impacts. These chemicals include pesticides like malathion, still widely used, and chlorpyrifos, which is only now being phased out of agricultural use.

Effects on sperm parameters are particularly pronounced for individuals in farming regions or with a history of occupational pesticide work.

However, studies on the general population also show cause for concern, finding total sperm count and concentrations inversely related to urinary metabolites of organophosphate insecticides.

Apart from sperm quality, the literature reveals several studies showing organophosphate exposure resulting in missing or extra chromosomes in sperm, with particular attention paid to diethyl phosphate, a non-specific organophosphate metabolite.

Synthetic pyrethroids are also singled out in the scientific literature for their links to sperm damage. These are the insecticides that are replacing the organophosphates, as they are being phased out for their myriad health hazards.

Unfortunately, the game of whack-a-mole played by the pesticide industry with the U.S. Environmental Protection Agency’s allowance has not resulted in chemicals that are safer for long-term human fertility.

Like organophosphates, occupationally exposed individuals are particularly affected, with pyrethroid factory workers showing higher rates of sperm abnormalities and lower motility than non-exposed individuals. Factory workers are also more likely to exhibit DNA fragmentation in their sperm.

Another concentration-dependent relationship is found, with individuals reporting higher levels of urinary 3-phenoxybenzoic acid (3-PBA), a non-specific pyrethroid metabolite, having a lower sperm counts, disomy and a greater chance of exhibiting sperm morphology below WHO thresholds.

Beyond these three classes, scientists did find evidence of negative associations with carbamate class insecticides, fungicides and herbicides, but the low number of studies does not allow for extensive analysis. Mixtures of various pesticides are cited as having similar effects to the three main pesticide classes investigated though firm results were difficult to specify due to lack of complete information.

In general, occupationally exposed workers are most at risk, with chronic exposure being associated with greater sperm defects.

The results of the study are concerning in light of steadily declining sperm counts. A 2017 study found that sperm counts since 1973 have fallen by nearly 60%.

One author of that study, Shanna Swan, Ph.D., captured public attention regarding sperm declines through her book “Countdown,” which goes into great depth regarding the impact of environmental chemicals on human fertility.

Watch Dr. Swan’s talk, “Modern Life and the Threat to the Future,” at Beyond Pesticides’ 2021 National Forum, Cultivating Healthy Communities.

Researchers have been sounding the alarm on the impact of pesticides on fertility for decades. In 2013, a previous literature review evaluating pesticide impacts on fertility found pesticides strongly associated with declines in sperm count. 

As she recounted in a presentation at Beyond Pesticides’ 2021 National Pesticide Forum Dr. Swan’s own work is borne out of efforts to try to disprove a paper published in 1992 by Carlsen et al., which highlights significant declines in sperm quality since the late 1930s.

As the human civilization grapples with a range of cascading crises, from climate change to the insect apocalypse and global biodiversity crisis, we may be missing the chance to address one of the most critical aspects to the continuation of humanity as we now know it.

Originally published by Beyond Pesticides. 

from:    https://childrenshealthdefense.org/defender/male-fertility-toxic-pesticide-chemical-exposure/

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Men & Menopause

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Hot Flash! Men May Be Cause of Menopause

Tia Ghose, LiveScience Staff Writer
Date: 13 June 2013
older man on date with woman
 Through history, older men have, on average, tended to partner with younger women, which may have led to the evolution of menopause, new research suggests.
CREDIT: auremar | Shutterstock.com

Ladies, here’s one more thing you can blame on men: menopause. At least, that’s according to a new theory.

Women go through menopause because men have consistently preferred younger women in recent evolutionary history, according to a study published today (June 13) in the journal PLOS Computational Biology.Thus, menopause is not evolutionarily advantageous and may be the result of a series of random, harmful mutations that accumulated in women but weren’t acted on by evolution because the women had already reproduced by the time the mutations affected them.

“Our first assumption is that mating in humans is not random with respect to age, which means men of all ages prefer to mate with younger women,” said study co-author Rama Singh, an evolutionary biologist at McMaster University in Canada. “If mating is with younger women, any deleterious mutations which affect women’s reproduction later in life will accumulate because they are not being acted on by natural selection.”

Menopausal mystery

Menopause, in which women stop menstruating and become infertile, has been a long-standing puzzle for biologists: Why would evolution have led to a trait that essentially reduces the reproductive potential of an animal?

Most other animals don’t go through menopause (although killer whales do). Even chimpanzees, humans’ closest living relatives, seem to reproduce into old age in the wild, and males even prefer older females.

Biologists have proposed the grandmother hypothesis to explain the conundrum. The hypothesis holds that menopause allows a grandmother who is done rearing her own kids to help rear the young of her children, thereby increasing the survival odds of her grandkids, and therefore, her genes.

But grandchildren and grandparents share just a quarter of their genes, versus half for children and their parents, so menopause would have to dramatically boost survival of grandchildren to be evolutionarily advantageous. Past studies have shown that maternal grandmothers boost their grandkids’ survival rates, though exactly how much depends on the society.

Younger women

For thousands of years (at least), men have, on average, mated with younger women, Singh said.

That’s because, if all else is equal, “those who reproduce earlier, their genes are passed on faster,” Singh told LiveScience.

So the researchers created a computer simulation to model that preference.

Early on, both men and women in the model reproduced until death. But over time, the model found, men’s preference for youth reduced older women’s odds of reproducing.

Simultaneously, people accumulated random mutations, some of which decreased later-life reproductive ability. But since older women were left out in the cold anyways, those mutations didn’t impact their reproductive success, whereas mutations in men that could reduce late-life reproduction were weeded out. (Men who stopped reproducing at some point in life would produce fewer offspring than those who didn’t, and the late reproducers would outcompete those who stopped breeding earlier.)

Over 50,000 to 100,000 years, the accumulation of all those mutations could have led to universal menopause, the researchers suggest. Menopause would then be another form of aging akin to graying hair or wrinkles.

If later childbearing becomes the norm, as current societal trends suggest, women who can reproduce at older ages might gain an evolutionary advantage, and menopause could, in theory be pushed later, Singh said.But it’s more plausible that technological changes such as fertility treatments will artificially extend women’s ability to reproduce, Singh said.

Questionable assumptions

But the new model might have the causation reversed, wrote Kristen Hawkes, an anthropologist at the University of Utah, who was not involved in the study, in an email to LiveScience.

As human life spans increased, women might have had many healthy years after fertility. As a result, men grew to prefer younger women because older women couldn’t reproduce.

Supporting that hypothesis, female chimpanzees see their egg reserves decline around the same age as human females, Hawkes noted. But unlike humans, they die shortly after this age, whereas humans have decades of healthy life left.

“The preference men have for young partners is a striking contrast with other primates,” Hawkes said. “My guess about that has been it’s a consequence of our life history.”

from:    http://www.livescience.com/37430-male-preference-younger-women-menopause.html