How harmful can those phytoestrogens really be to mammals? They can decimate an entire population of mammals.
Chapter 5: Fifty Ways to Lose Your Fertility (Could also be called Fifty Ways to Derail a Healthy Pregnancy from Theo Colborn’s Our Stolen Future)
The early 1940s seemed like a particularly promising time for the sheep ranchers in the gentle rolling hills south of Perth in western Australia. Three unusually good seasons had followed one after another, and with the favorable weather, the pastures exploded into lush, green growth, allowing the sheep to graze for an exceptionally long time. According to ranchers in the region, the sheep—handsome, burly merinos that produce fine, luxurious wool—had never looked so good.
But just when things had never been better, a strange epidemic began hitting the flocks—an epidemic of infertility. The first sign was a striking increase in stillborn lambs. Then the ewes carrying lambs failed to go into labor; the lambs died and often the mothers as well. Each year the problem worsened until finally, even after repeated breeding to fertile rams, most of the ewes simply did not conceive at all. In a matter of five years, the breeding program stopped cold, and ranchers in the area faced financial disaster. Without the irrepressible exuberance of the gamboling lambs, spring did not really seem like spring.
After extensive detective work that involved not only state agricultural specialists but federal scientists as well, researchers finally determined that the cause of the sterility epidemic wasn’t found in poison or disease or a genetic defect. The cause was clover….
The first scientific paper on this phenomenon appeared in the Australian Veterinary Journal in 1946, but it took several more years to isolate three chemicals suspected of causing infertility. In the end, however, researchers determined that only one of these chemicals, formononetin, was the culprit. This natural compound, which escapes breakdown in the sheep’s stomach, can, like DES and DDT, mimic the biological effects of estrogen.
Surprisingly, plant evolution had produced chemicals that mimic estrogen long before Dodds synthesized DES in the laboratory, and not just one or two, but many—twenty of which are now known to science. To date, researchers have found these estrogenic substances in at least three hundred plants from more than sixteen different plant families. The list includes many foods that feed the world as well as some of our favorite herbs and seasonings. Hormone mimics lurk in parsley, sage, and garlic; in wheat, oats, rye, barley, rice, soybeans; in potatoes, carrots, peas, beans, and alfalfa sprouts; in apples, cherries, plums, and pomegranates, and even in coffee and bourbon whiskey. Like DES and DDT, these plant compounds can fool the estrogen receptor.
So why are plants making estrogens?
“Plants are making oral contraceptives to defend themselves,” says Claude Hughes, a researcher exploring the effects of hormone-like compounds on the reproductive system. It might sound like a wild idea, but from an evolutionary perspective it makes sense.
Since plants cannot escape predators by running away, they have evolved a fascinating variety of defenses. Some smell bad, taste bad, or poison those that eat them. Others have unpalatable thorns, spines, or indigestible substances in their leaves. When insects attack, many plants fight back with a chemical arsenal the can kill insects outright, making them stop feeding, or disrupt their growth by mimicking insect growth regulator hormones. This growth disruption typically makes an insect sterile, thus reducing the troubling insect population.
The more Hughes explored the notion that plants might be making contraceptives, the more evidence he found consistent with the theory that this is indeed what plants are up to. By lacing their leaves with hormonally active substances, they suppress the fertility of the animals that feed on them. By Hughes’s theory, clover disease isn’t simply an unfortunate livestock malady, it is a subtle and previously unrecognized form of plant self-defense. The plants that make estrogen mimics, he notes, are tasty ones sought out by animals and humans for food, not the unappetizing plants that contain foul-tasting compounds—an alternative defensive strategy….
The thought that plants might be making chemicals aimed at undermining fertility of their predators first occurred to Hughes while he was a doctoral student studying the impacts of marijuana on the brain. Humans have long used marijuana as a drug because the chemical it contains act in the brain to alter mood and perception, creating a “high.” But as Hughes and others, discovered, these chemicals do more than induce a pleasant mellowness; they interfere with reproduction in a wide variety of ways. The same compound that makes a pot smoker high also acts on the testicles to reduce the synthesis of testosterone and on the brain to suppress lutenizing hormone, a key hormone that cues ovulation in females and testosterone production in males. Studies have reported that marijuana feminized males who smoked it heavily.
Hughe’s work focused on the way the marijuana interferes with the hormone prolactin, which is produced in the brain and signals the breast to produce milk. Mother rats given marijuana produced no milk, and their pups died of starvation. Hughes later moved on to investigate the effects of plant estrogens on the endocrine system and the hormones that orchestrate reproduction, an area few scientists had explored.
For a defensive strategy to work, he explains, the plant would logically target females rather than males because a predator’s reproduction is limited by the number of fertile females. If, for example, a plant managed to impair of all the males save one, that single male can, nevertheless, fertilize an entire flock of females. But if only a single female is fertile, she can produce only one or two lambs.
Plants containing estrogen mimics produce them according to a seasonal pattern that fits perfectly with this strategy. Clover packs the greatest concentrations of estrogenic compounds into the new growth in spring, and when a rabbit or sheep injures it by munching on these tender shoots, the plant responds by producing even more estrogen at the site of injury, delivering an added dose to predators that continue grazing….
Historian John M. Riddle of North Carolina State University reports that women throughout the ancient world used a variety of plants to prevent pregnancies and precipitate abortions, including a now extinct giant fennel called silphium. Researchers have confirmed that many plants in the fennel family produce estrogenic substances or other hormonally active compounds. The ancients also used wild carrot, the beautiful and delightfully common weed known as Queen Anne’s lace, which the Greek physician Hippocrates, who lived in the fourth century B.C., described as having similar powers. Studies have shown that its seeds contain chemicals that block the hormone progesterone, which is necessary for establishing and maintaining a pregnancy.
The pomegranate played a central role in both Greek myth and their birth-control efforts. According to the myth, Persephone, the daughter of the fertility goddess Demeter, was told to eat nothing during a visit to the underworld Hades, but she disobeyed and ate a pomegranate. As punishment, the gods sentenced her to spend part of the year in the underworld, and for this reason, Earth experiences the barren season of winter until Persephone returns each spring. Riddle says the Greeks used pomegranate as a contraceptive, and here again studies have found that it contains a plant estrogen that acts like the chemicals found in modern oral contraceptives manufactured by the pharmaceutical industry.
“Sheep infertility from pasture legumes.” Infertility from subterranean clovers. Some older varieties of subterranean clover (and most red clovers) contain high levels of phyto-oestrogens, which can affect the sheep reproductive system.”
Clover infertility was a severe problem in the 1960s for sheep grazing subterranean clover-dominant pastures, particularly on new land. These pastures were often dominated by the highly oestrogenic Dwalganup or
Yarloop cultivars.
In some ewes, the uterus prolapsed through the vulva while other ewes suffered dystokia (difficult lambing) and appeared unable, or disinterested in, delivering their lambs. Frequently, the lamb and ewe died before delivery. Other ewes became infertile and lamb marking rates fell to 20 – 40 per cent, in a condition known as ‘clover disease’.
Some wethers also died because of swollen bulbourethral glands and blocked urethras. When the subterranean clover content of pastures declined, signs of clover infertility also decreased.
(Very special thanks to the WayBack Machine for archiving this! It’s no longer available elsewhere, of course.)
The Silent War 