The environment in which your great-great-grandmother lived, breathed, ate and drank might be responsible for health problems endured by you, your children, even your children's children.
This is the disconcerting conclusion of a preliminary study, which experts say could help shift our understanding of disease -- reproductive disorders, in particular -- as well as how we perceive the consequences of everyday choices such as drinking out of a plastic water bottle.
"People can be cavalier with their own health," said Bruce Blumberg, a biologist at the University of California, Irvine, who was not involved in the study. "But it's not just ourselves that are at risk. We're condemning our descendants to have increased risks, too."
Scientists today are uncovering a host of potential new links between environmental exposures in the womb and health problems later in life, from bisphenol A (BPA) encouraging obesity to pesticides precipitating cognitive problems.
The new research takes this notion a step farther -- or many generations into the future.
Published on Thursday, the study exposed pregnant rats to high levels of prevalent plastics (BPA and phthalates), pesticides (vinclozolin, permethrin and DEET) or a notorious pollutant (dioxin), and then looked to see what influence the one-time exposures had on the ovaries of future generations. Of particular interest was a condition known as polycystic ovary syndrome (PCOS), which is itself implicated in a range of health problems including infertility, obesity and diabetes. PCOS has been on the rise over the last couple decades and now affects an estimated 8 to 18 percent of adult women.
The researchers found each of the environmental toxins triggered ovarian disease in future generations. Interestingly, the effects in the third generation -- the first rats not to be directly exposed to the chemicals -- were more pronounced than in the offspring of the exposed rat.
In addition to PCOS, the team also identified rats with the second-most common ovarian disease, also implicated in infertility: primary ovarian insufficiency.
"Ovarian disease, just like many diseases, are primarily thought to be due to genetic abnormalities," said Michael Skinner, a biologist at Washington State University and senior researcher on the study. "This study suggests it is probably more of an environmentally induced phenomenon."
Injections of the compounds into pregnant rats, in fact, did not alter the genes. Rather, the exposures changed how these inherited instructions for life were interpreted by the next generation.
Previous studies of this so-called epigenetic effect have found that the defective programming can be repaired down the family line. John McCarrey, a biologist at the University of Texas, San Antonio, recently published a study in which he actually witnessed such corrections being made as one generation gave rise to the next. Different timing of the single exposures in the new study, he suggested, could explain why the mixed-up signaling wasn't fixed.
"These epigenetic defects are more serious than we thought. It's bad enough that these problems are going on in any individual," said McCarrey. "Having them occur in descendants, that's pretty profound."
Skinner's team is finding evidence of a similar phenomenon leading to kidney and prostate disease, breast cancer and obesity, among other health problems. However, he emphasized that none of the findings to date offer proof that the same permanent flaws would play out in humans. More studies are needed, including research into the levels of exposure necessary to cause harm.
This issue of dosage may further confuse already complicated matters. Growing evidence questions an old assumption that the dose makes the poison. As The Huffington Post reported, even minute amounts of hormone-mimicking chemicals such as BPA appear to be more potent than larger quantities, and can scramble human hormones and cause a host of health problems.
Skinner saw a similar phenomenon in his study: "With the plastics, the lower doses actually gave us a more dramatic effect than the higher doses."
Tracey Woodruff, a reproductive health expert at the University of California, San Francisco, also noted that investigations into how toxic exposures affect a fetus have pointed to the significance of low doses.
She went on to applaud the new study. "There is so little known about the role of the environment on the female reproductive tract and these types of problems: fibroids, PCOS and endometriosis," said Woodruff, whose recent work describes what pregnant women can do to limit environmental exposures. "This research adds data to something we suspect to be the case but for which there is little research."
Some experts suggest that the new research provides new arguments for stricter regulations on certain chemicals.
"This raises the bar," added Blumberg. "Industry likes to say that the risk isn't so big or the exposures are not so high. But, in fact, these exposures can have far-reaching effects. Unfortunately, regulators are having difficulty even coming to sensible conclusions on direct effects, let alone transgenerational ones."