The Emerging Evidence Of BPA's Effects On Human Development
Over the course of many decades, synthetic chemicals like bisphenol A became ubiquitous in American life. This particular chemical, an organic compound often called BPA, is commonly used in plastic food and water containers, in the linings of food cans and water pipes, and in the plastic components of medical equipment, among many other applications. When these objects are heated, the chemical can leach into food, drinks and intravenous fluids.
When BPA and chemicals like it get into the human body, though, they can bind with hormone receptors in living cells and interfere with the endocrine system. This exposure is increasingly recognized as a potential threat to the physical and mental development of infants and children, which can have serious implications for their long-term quality of life.
Researchers are still working to better understand the impacts of BPA and other endocrine-disrupting chemicals. In animal experiments, petri dish assays and long-term surveys of children who were exposed to BPA in the womb, a picture is gradually emerging of how this and similar substances can affect human development in numerous ways, from fertility to aggressive behavior. This body of research is hardly conclusive in the details, but it's clear that too much of these chemicals in a human body is dangerous, as University of Wisconsin-Stevens Point psychology professor Heather Molenda-Figueira discussed in an April 12, 2016 talk at the Portage County Public Library.
In her presentation, recorded for Wisconsin Public Television's University Place, Molenda-Figueira detailed chemical and biological processes that make endocrine disruptors harmful, and delved deep into the myriad health problems they've been linked to in a plethora of human and animal studies. She also explained why those "BPA-free" plastic bottles aren't necessarily harmless either, as some of them use a similar chemical called bisphenol S, or BPS. While some research indicates that BPS is less dangers than BPA, researchers are still trying to understand its effects.
Molenda-Figueira discussed her research into whether endocrine disruptors have a significant effect on anxiety disorders. Specifically, she studied the effects of BPS on rats to see whether it affected anxiety. The results did not establish a connection, but Molenda-Figueira plans to continue her investigations.
- An endocrine disruptor is a chemical introduced to a body from an external source that interferes with synthesis, secretion, transport, metabolism, binding action or elimination of natural blood-borne hormones that are responsible for homeostasis, reproduction and developmental processes. When these chemicals enter a body, they bind with hormone receptors, which interferes with processes that trigger hormone-dependent gene expressions and behaviors.
- Not all endocrine disruptors come from human-made chemicals — some are naturally occurring. For example, genistein occurs in soy-based foods, and it can bind to estrogen receptors.
- Plastics are a major manufactured source of endocrine disruptors like BPA, including the lining of food cans, medical supplies like syringes and medical tubing, and children's toys. Cosmetics and personal care products, including lotions and soaps, can also have endocrine-disrupting chemicals in them. (The FDA currently approves the use of bisphenol A in materials that come into contact with food products.)
- BPA has been found in human blood, urine, amniotic fluid, fat tissue and placental tissue. The chemical can actually cross the placental barrier from a mother to a developing fetus, and infants can be exposed to BPA through breast milk as well.
- Exposure to endocrine disruptors can impact neural development in infants and children. They can cause problems with memory, potentially contribute to the development of ADHD, and are associated with lower IQs.
- Endocrine disruptors play a role in cancer risks, especially hormone-dependent types like breast cancer, prostate cancer, and testicular cancer. BPA has also been linked with higher risks of obesity and diabetes.
- BPA and pthalates (another class of endocrine-disrupting chemicals) can impact pregnancy outcomes, fertility, and birth rates in both mothers and their children. Some research has correlated exposure with higher likelihoods of pre-term birth, as well as connecting BPA with endometriosis, a condition involving painful buildup around a woman's uterus and other reproductive organs. Other research shows that exposure to these chemicals can promote earlier onset of puberty in girls. Earlier puberty has been connected with reproductive cancers and psychological disorders like depression. Pthalate exposure has been associated with smaller penis size, undescended testes, lower testosterone and the development of breasts in males. It can also decrease fertility in men and women.
- Studies across different age groups have found that infants, toddlers and children have the greatest exposure to BPA through food. These exposure levels were below what the Centers for Disease Control and Prevention deems as safe levels, which is about 50 micrograms per kilogram of body weight per day. Compared to adults, infants, toddlers and children tend to eat more food as a proportion of their body weight, and they're more likely to consume foods that might include BPA.
- BPA exposure has been tied to an overproduction of neurons in the hypothalamus, an area of the brain that regulates metabolic processes related to hormone production and social behavior. An excess of neurons can harm the brain's development in utero. The brain is supposed to lose some neurons during development as it becomes more efficient, but with an excess of neurons, that process can become disrupted.
- Infants who've been in a neonatal intensive care unit have higher levels of BPA exposure because of the presence of the chemical in medical products.
- BPA can also alter the regulation of the brain's mood and reward systems. It specifically alters the function of dopamine receptors, which can make a person feel a greater sense of reward from various drugs, including methamphetamine and morphine.
- Studies on people whose mothers had higher levels of BPA in their urine found higher levels of anxiety and depression, as well as social problems like increased aggression and emotional reactivity. The chemical has also been linked to attention and hyperactivity problems, and difficulties in reading, writing and math. However, different studies on people have produced different results, especially diverging along gender lines — some studies showed greater effects in girls than in boys.
- Animal studies show BPA exposure increases aggressive behaviors in both males and females. It makes females more receptive to sex, and males less interested in sex. It also tends to increase exploratory behavior in females.
- Concerns about BPA have led many companies to remove it from their products, but it is often replaced with the structurally similar BPS, which is a bit more heat-resistant, and therefores less likely to leach into food or drinks. However, it's also less biodegradable. BPS can still make its way into the human body. Like BPA, it can have estrogenic effects. In research on fish, BPS has also been connected to lower testosterone in males, lower fertilities and brain development issues. The chemical has also been shown to increase uterine growth in rats, suggesting that it could increase risks of endometriosis in females, similar to BPA.
- On how widespread BPA is: "In the U.S. it's one of the highest volume chemicals produced and it is found in a variety of products, including plastics, where it's used to make plastics more heat resistant and clear. So it's found, again, in water bottles and containers that are used to house food, plastic food packaging. BPA is also a component of PVC, and it also is part of the epoxy resins that line food cans and beverage cans." [The National Institute of Health's National Library of Medicine notes BPA is used to make PVC plastic products.]
- On the health concerns surrounding endocrine disruptors: "Exposure to these endocrine-disrupting chemicals can cause things to go awry at many different levels. Exposure to endocrine-disrupting chemicals can disrupt things like lactation, sexual maturation, also reduce fertility, as well as potentially increase the risk for psychological disorders."
- On the presence of BPAs in medical supplies like medical tubing: "When endocrine disruptors leach out of these plastics into the fluids that pass through these medical supplies they're going right into your bloodstream, so probably not such a good thing."
- On personal care products: "In this case we kind of get a double whammy, because a lot of these products also are housed within plastic bottles, so that's one source, and then the products themselves often contain fragrances, and fragrances is another source of phthalates, one of those endocrine-disrupting chemicals."
- On exposure to EDCs in the womb: "One of the most harmful time points for exposure to these EDCs tends to be during in utero development. This is a time point when there's a lot of changes in the brain going on, and one area in which some of these EDCs can affect development is the hippocampus, which some of you might already know is important for memory."
- On animal-based studies into the effects of BPA exposure: "Typically in these studies what occurs is that animals are exposed to BPA either during gestation, through administration to the mom, or shortly after birth. These are important time points for the development and organization of brain circuits, including organization in the brain in terms of circuits that are necessary for learning, memory, and social behaviors. It is also during this time point that their sex differences in the brain become apparent."
- On focusing on anxiety in her rat-based studies investigating BPS: "Why I chose to look at anxiety is because it's one of the most prevalent psychiatric illnesses in the U.S. population, with about 16 million people suffering from the disorder."
- On steps people can take to reduce their BPA and BPS exposure: "Number one, we can avoid plastics that have their recycling labels numbered 3, 6, and 7. Safer bets are numbers 1, 2, [4 and 5]. We can also look for glass or metal containers for our food and drink. Next, we can avoid microwaving our food in plastic containers or washing plastic containers in dishwashers with harsh detergents; so again, heating up these plastic components or plastic products is one way to promote the leaching of these chemicals into your food sources. Next we can reduce or eliminate the consumption of canned foods and try to eat more fresh foods or frozen foods. And finally, with concerns for exposure to children, you can look for BPA- and BPS-free baby bottles, as well as toys."
[Editor's note: This item was updated with additional information about the use of BPA in making PVC plastic products.]