¿Te has preguntado si existe una manera natural de bajar tus niveles de presión arterial, protegerte contra el alzhéimer, perder peso y sentirte mejor? Resulta que sí la hay. El doctor Michael Greger (FACLM), fundador de NutritionFacts.org y autor del rotundo éxito de ventas del New York Times "How Not to Die" (Comer para no morir), nos presenta la nutrición basada en la evidencia para añadir años a nuestra vida y vida a nuestros años.

Hello and welcome to Nutrition Facts.  I’m your host, Dr. Michael Greger.  Today, we’re going to explore smart nutrition choices based, naturally, on facts.  Have a history of high blood pressure in your family?  How about heart disease?  Diabetes?  There are foods we can eat that may not only help prevent many of these chronic diseases but even stop them in their tracks. 

Today, we take a close look at BPA, the compound that has been used in industrial chemicals to make certain plastics and resins since the 1960’s.

Research suggests that BPA is linked to billions of dollars’ worth of medical problems a year.  So why is it still allowed in the food supply?  Here are some answers.

“The number of new chemicals is increasing exponentially”—we’re talking 12,000 new substances a day. Yet, data aren’t available on the hazards of even some of the high-volume chemicals. BPA is one of the highest-volume chemicals, with billions of pounds produced each year. And, studies have “raised concerns about its possible implication in the [cause] of certain chronic diseases, such as diabetes, obesity, reproductive disorders, cardiovascular diseases, birth defects, chronic respiratory and kidney diseases and breast cancer.”

A new study on the health implications of BPA comes out nearly every week. BPA was first developed over a hundred years ago as a synthetic estrogen. But it wasn’t until the ‘50s that industry realized it could be used to make polycarbonate plastic, and it rapidly became one of the most used chemicals worldwide, even though it was recognized to have hormonal effects. About a billion pounds are also used to line food and beverage cans—especially, it seems, in tuna and condensed soups.

And now, we basically all have BPA in our bodies, and our children’s bodies. But, not to worry; the government says up to 50 a day is safe (50 micrograms per kilogram). And, even those working in Chinese BPA factories don’t get exposed to more than like 70 times lower than that safety limit. Okay, then, why did exposure seem to affect the male workers’ sperm counts?

In the U.S., the general population only gets less than like a thousand times lower than the safety limit. Yet, still, we seem to be seeing adverse effects on thyroid function, weight control, blood sugar control, cardiovascular disease, liver function, and immune function —even at those incredibly low doses. So, “the fact that there are significant adverse effects in populations exposed to BPA at concentrations [thousands of] times lower than the [official tolerable daily limit] indicates that the safe exposure to BPA may be much lower than previously thought in humans.” Yet, the limit hasn’t been changed. It’s been banned from baby bottles and sippy cups, but nearly unlimited doses are still apparently okay for everyone else. What’s the disconnect here?

It has to do with the fascinating world of low-dose effects of hormone-disrupting chemicals. “For decades, [these chemicals] “have challenged traditional concepts in toxicology”—particularly the old adage that it’s the dose that makes the poison, the concept “that lower exposures to a hazardous compound will, therefore, always generate lower risks.” That’s “the core assumption underlying [our] system of chemical-safety testing.” They start dosing lab animals with super high amounts, and then keep lowering the dose until whatever adverse effects disappear; then, add a safety buffer and assume everything below that dose should be okay, assuming the curve looks like this. You know, the higher the dose, the higher the effect. But, hormone-disrupting chemicals can have all sorts of “curious curves.”  Wait a second.  How could something have more of an effect at a lower dose?

Think about a hormone and its receptors in the body. At low levels of the hormone, like going from 0 to 1, the receptors can fill up quickly. But, once they’re almost all filled up, going from 4 to 5, adding really high doses may not change things much. Let’s use an actual BPA example. This was a study to see if BPA suppressed an obesity-protective hormone in fat samples taken from breast reduction and tummy tuck patients. 

As the world’s oldest, largest, and most active organization devoted to research on hormones concluded, “even infinitesimally low doses of exposure—indeed, any level of exposure at all—may cause [problems],” nearly three billion dollars’ worth of problems every year, just counting the estimated effects of BPA on childhood obesity and heart disease alone.

Now, there are alternatives that the industry could use; the problem, though, is that they may cost 2 cents more. 

Using skin lotion or hand sanitizer before touching thermal paper (like cash register receipts and printed tickets) can facilitate the absorption of BPA into the body.  Here’s the story. 

The plastics chemical BPA was banned from baby bottles in Canada in 2008, in France in 2010, in all of Europe in 2011, and in the United States in 2012. But in 2015, France forbid the use of BPA “in any food or beverage packaging”—something the U.S. FDA decided was not warranted. But, what about the 90+ studies reporting links between BPA levels in people’s urine, with a wide array of adverse health outcomes—”including a[n apparent] significant increase in the likelihood of developing [heart disease] and…diabetes, obesity, impaired liver, immune, and kidney function, inflammation, reproductive effects in women…and men…, and altered thyroid [function], and [developmental] deficits in children, such as aggressiveness, hyperactivity, and impaired learning.”

Only a very small minority of studies appear to support the federal government’s assertions that there were no effects at low doses. So, where’s the disconnect? Governments determine safety levels by sticking tubes down into the stomachs of lab animals. The BPA is released directly into the stomach, where it goes to the liver to be detoxified into an inactive form, called BPA-glucuronide. So, very little active BPA gets into the bloodstream.

But, that’s not what studies on humans show—people have active BPA in their blood. And so, the FDA response was to reject all such human studies as implausible. The problem with a blanket rejection of human data is that there may be sources of BPA exposure that are not modeled by stomach tube exposure in rats. After all, “[T]his isn’t how food enters our bodies,” actually. “We chew it, move it around in our mouths…before it enters the stomach.” And, it turns out “BPA can be completely absorbed directly into the bloodstream from the mouth,” thus bypassing instant liver detoxification. The same would be the case for BPA absorbed through the skin.

So-called thermal paper is 1 to 2% BPA by weight. That’s like “cash register receipts, luggage tags, [and] bus/train…lottery tickets.” Taking hold of a receipt can transfer BPA to our fingers, especially if they’re wet or greasy. But, does it then get absorbed into our system through the skin?

Well, cashiers were found to have more BPA flowing through their bodies. But, that was just based on a few people. Same problem with studies showing those eating plant-based diets having lower levels: too small of a sample size really to make a conclusion. It’s been estimated that even cashiers handling receipts all day long may not exceed the tolerable intake. However, if they’re using something like hand cream, that could change.

“…[M]any skin care products…hand sanitizers, lotions, soaps and sunscreens, contain…chemicals that [enhance skin penetration].” So, using a hand sanitizer before touching a receipt could, in theory, cause a breakdown of the skin barrier. Theoretically, that is—until now.

We now know that holding a receipt and eating food, after using hand sanitizer, results in high blood levels of active BPA. Researchers at the University of Missouri “conducted [a] study to mimic aspects of the behavior of people in a fast-food restaurant where [they’ve] observed people using [a] hand sanitizer,…handling a…receipt,…and then eating food with their hands.” They found that when people handled the receipt right after using Purell, BPA was transferred to their fingers, then fries, and then the combination of absorption through the skin and the mouth led to significant levels of active BPA in their blood.

You can hold a receipt in your hand for 60 seconds and only come away with 3 micrograms in your body. Whereas, if you pre-wet your hands with hand sanitizer, you get 300 in just a few seconds—a hundred times more. These findings show that just a few seconds touching a receipt after using something like hand lotion could transfer large amounts of BPA.

And so, this could explain why dozens of human studies show active BPA in people’s systems—contrary to the assumptions based on stomach tube studies in rodents. When actual evidence contradicts your assumptions, you reject the assumptions. But, what the FDA did was instead reject the evidence.

Here’s our next question: Do BPA-free plastics, such as Tritan, have any human hormone-disrupting effects? And what about BPS and BPF?  Here’s the research.

“Recent human studies indicate that…exposure [to the plastics chemical BPA] may be associated with…[infertility], miscarriage, premature delivery, reduced male sexual function,…[polycystic ovaries],…altered thyroid…and immune function,…diabetes,…heart disease,” and on down the list.

Yet, “[a]s recently as March 2012, FDA stated that low levels of BPA in food are considered safe.” But, months later, to their credit, “the agency banned the use of BPA [plastics] in baby bottles and sippy cups.” Wow, regulators standing up to industry! Maybe I shouldn’t be so cynical. Oh, wait, the ban was at the behest of the plastics industry. They had already stopped using BPA in baby bottles; so, ban away—it was their idea.

What they did is switch from BPA to similar compounds, like BPF and BPS. And so, now our diet contains everything from BPA to BPZ. So now, the majority of us have these new chemicals in our bodies, as well. Are they any safer?

Well, based on the similarities of their chemical structures, they are all predicted to affect testosterone production and estrogen-receptor activity. But, only recently were they put to the test.

We’ve known BPA significantly suppresses testosterone production. And now, we know so does BPS and BPF—”the first report describing…adverse effects on a physiologic function in humans…” Well, kinda. These were experiments performed on the testicles of aborted human fetuses. But, bottom line, BPS and BPF seemed to have similar “antiandrogenic”—meaning anti-male hormone—effects to BPA.

So, when you’re assured that, “Don’t worry, your sales slip at the store was ‘BPA-free,’” it may be just BPS instead. And, BPS receipts “may contain up to 40% more” BPS than it would have had BPA. So, BPA-free could be even worse! In fact, all BPA-replacement products tested to date released chemicals “having reliably detectable [estrogenic activity].”

And, this includes Tritan™, which is specifically marketed as being estrogen-activity free. But, drip an extract on human breast cancer cells in a Petri dish, and you can accelerate their growth—an effect that’s abolished by an estrogen blocker. Now, this was after exposing them to simulated sunlight. Only one out of three Tritan products showed estrogen activity in an unstressed state—not exposed to microwaving, heat, or UV rays.

“Because there would be no value in trading one health hazard for another, we should urgently focus on the human health risk assessment of [all these] BPA substitutes.”

In the meanwhile, there are steps we can take to limit our exposure. We can reduce our “use of polycarbonate plastics,” which are usually labeled with recycle codes 3 or 7, and opt for fresh and frozen food, over canned goods—especially tuna and condensed soups.

Canned fruit consumption didn’t seem to matter, but weekly canned vegetable consumption was associated with increased BPA exposure. If you do use plastics, don’t microwave them, don’t put them in the dishwasher, don’t leave them in the sun or a hot car, or don’t use once scratched.

To see any graphs, charts, graphics, images, or studies mentioned here, please go to the Nutrition Facts podcast landing page. There, you’ll find all the detailed information you need plus links to all the sources we cite for each of these topics.

NutritionFacts.org is a nonprofit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.

Everything on the website is free. There are no ads, no corporate sponsorship. It’s strictly non-commercial. I’m not selling anything.  I just put it up as a public service, as a labor of love, as a tribute to my grandmother, whose own life was saved with evidence-based nutrition.

Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.

This is an approximation of the audio content, contributed by Allyson Burnett.

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