Can chemicals in plastics act as endocrine disruptors? Yes. What does that mean to your body? Much of the research is pointing to disruptive activity in relation to estrogens, androgens, and thyroid hormones. In addition, concerns include adverse consequences for male and female reproductive health, brain development/function, thyroid function, metabolic alterations, immune responses, and cancers in hormone-sensitive tissues.
Let’s take a close look at this critical health issue facing us today.
Endocrine disruptors
An endocrine disruptor is defined as: “an exogenous substance that causes adverse health effects in an intact organism, and/or its progeny, consequent to changes in endocrine function.”
Multicellular organisms depend upon a healthy endocrine system for normal growth, development, and maintenance. Recently, research has shown that certain chemicals like bisphenol A (BPA) and phthalate esters can interfere in hormone action. These endocrine-disrupting chemicals act upon hormone synthesis in the endocrine gland and change the transport, metabolism, and excretion of the hormone. They may also compete with the physiological hormone for binding to receptors in target cells. Thus, they mimic or antagonize hormone action.
Much of the research has been regarding BPA and the phthalate esters and estrogens, androgens, and thyroid hormones, which can result in problems with underlying diabetes, cardiovascular disease, and obesity, impaired brain development/function, compromised immune responses, and to cancers in hormone‐sensitive tissues. The window of susceptibility for exposure seems to be in utero and the early postnatal period. The symptoms may not be apparent until adulthood.
Endocrine-disrupting chemicals (EDC) like the ones above typically are found in plastics and polyvinyl chloride as they provide properties like flexibility, durability, and lighter weight. They are also found in consumer products like adhesives, paints, air‐freshener products, and personal care products. Early research showed that BPA would leach out of plastic, and this has led to further investigations into additives that may leach from plastic to become contaminants in the environment and human system.
BPA as an endocrine disuptor
BPA dates back to the 1890s, and its estrogenic properties were first reported in the 1930s. Pharmaceutical companies sought chemicals with estrogenic properties for medical use. However, more potent chemicals like diethylstilboestrol (DES) were preferred to weaker formulas like BPA. DES was used to prevent miscarriage until scientists discovered that daughters of mothers who had taken DES developed a rare form of cancer. Other research found numerous reproductive abnormalities and cancers in sons as well as daughters following exposure in utero to this potent estrogen. This was a strong warning to the developmental consequences from in utero exposures to endocrine‐disrupting agents
However, BPA was not used as a drug. Instead manufacturers used it in epoxy resin and polycarbonate plastics in high volumes, which resulted in its wide distribution throughout human tissues and urine. Its ability to mimic physiological estrogens comes from its phenolic groupings, which determine binding to estrogen receptors. In vitro, it has been shown to bind to estrogen receptors ERα and ERβ, to stimulate estrogen‐dependent gene expression and to increase proliferation of estrogen‐responsive cells. However, it may also work through membrane estrogen receptors including the G‐protein‐coupled receptor GPR30 and through non‐genomic mechanisms.
In addition, BPA can amplify the expression of aromatase, the key enzyme necessary for converting androgens into estrogens, and it can bind to the androgen receptor and give antiandrogenic responses. BPA can bind to thyroid hormone receptors and interfere in thyroid function. Moreover, BPA can bind to and interfere with peroxisome proliferator‐activated receptors.
The sources of human exposure to BPA and phthalates
BPA and phthalates are common environmental pollutants, and human exposure may result from inhalation, ingestion, and absorption through the skin. Airborne BPA is so common that it has been detected in the polar regions. The highest levels exist in urban India. BPA is also widely present in food, following leaching out from the plastic packaging and is present at low levels in drinking water.
Phthalates are typically airborne and may be found in the indoor environment. One study in Richmond, VA found phthalates in 100% of the homes that were tested. Some phthalates are found in house dust, and PVC flooring has been implicated for raising levels in phthalates in homes. However, diet is the most common method of exposure, and the skin can absorb considerable levels from topical application of personal care products. Phthalate metabolites have been detected in almost all human urine samples, which means there is broad exposure to the population.
The impact on overall health and the consequences of early life exposure
Exposure to EDCs has long been a concern. In the 1920s to 1940s, farmers reported decreased fertility in their livestock after they ate plant‐based phytoestrogens. This led to further investigations into exposure to potent estrogenic compounds on human reproductive health.
Other concerns developed when exposure to pollutant chemicals resulted in reproductive failures in wildlife. Many of these chemicals had endocrine‐disrupting properties. However, the long‐term side‐effects of prescription of DES to women during pregnancy clearly showed the consequences for humans as well as animals. The link between fetal development and adult disease discovered in the 1990s showed the possibility of fetal origins in adult disease. The continuing legacy of DES showed that exposure to endocrine agents in utero could have long‐term effects well into adult life. Although endocrine‐disrupting agents have been linked to many human health problems, a recurring theme exists that there are windows of susceptibility in utero and in early postnatal life.
Some EDCs, now called obesogens, can interfere in the endocrine regulation of energy metabolism and development of adipose tissue architecture leading to weight gain and obesity in adulthood. Animal research has shown that early exposure to BPA can predispose animals to weight gain. Worse, transgenerational studies in rodents showed that this tendency towards obesity can be passed down through generations.
Epidemiological studies show that early‐life exposure to BPA is associated with increased weight gain in children. In addition, research has shown a relation between urinary concentrations of phthalate metabolites and increased waist circumference.
Other research indicates that early life exposure to EDCs may alter development of the brain and immune systems. Prenatal exposures to BPA and phthalates are now being linked to adverse cognitive and behavioral outcomes in children. Early life exposures to EDCs are being linked to suppressed inflammatory processes, which results in insufficient immune responses against viruses, bacteria, fungi, and cancer cells.
Furthermore, one study that used rodents exposed the pregnant females to BPA. The scientists noted that it modulated the innate immunity of their offspring against the influenza virus type A. This is truly important to study more fully as we study the effects of the global COVID-19 pandemic. Has exposure to EDCs negatively impacted our immune system and its response to the coronavirus? Have the symptoms been more severe for individuals with considerable exposure to EDCs?
Final thoughts
Plastics are so common in both indoor and outdoor environments, and it is clear that chemical additives can leach out into our environments as they age or in hotter temperatures. These chemicals can interfere with hormonal systems and the regulation of the entire human body. Our bodies may be able to tolerate minute levels of these pollutants, but the problems develop when exposure rises and use increases. In addition, the problems are compounded because many pollutant chemicals act by similar mechanisms, which facilitates the chemicals to have an even greater negative impact on the endocrine system through disruption.
One solution would be to replace the BPA and phthalate esters with other compounds lacking the endocrine‐disrupting properties. However, efforts to find substitutes have met with significant challenges.With our increasing dependence on plastic materials, consumers must be educated on ways of avoiding or reducing their exposures on a daily basis.
Although we have learned a lot over the past few decades regarding the potential consequences of exposure to EDCs such as BPA and phthalate esters. Additional scientific research must be conducted for greater clarity of specific associations and particularly in the assessment of mixtures. Adverse effects seem unlikely to result from single sources or even single chemicals but rather from long‐term low‐dose mixtures of chemicals with additive, overlapping, or complementary mechanisms of action. We must be very concerned and wary regarding the contribution of BPA and phthalate exposures to human health issues and find the underlying mechanisms of individual susceptibility.
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