Exposure to Bisphenol A and Its Concentration Levels In Relation to Polycystic Ovary Syndrome

Abstract 

Polycystic Ovary Syndrome (PCOS) is one of the most common disorders diagnosed in women. It is characterized by menstrual irregularities, hyperandrogenism, and infertility. A solidified reason as to why so many women develop PCOS has not yet been identified, but research suggests a significant connection with Endocrine Disrupting Chemicals (EDCs). This literature review examines research on BPA, which is one of the most common EDCs in the world and is frequently used in a wide range of utilities. Research groups used its concentration to further identify the values in urine and blood samples between women with PCOS and healthy women. Across almost all studies, women with PCOS were found to have significantly higher levels of BPA in blood and urine samples than healthy individuals. Although clear causality remains debated, these findings can help clarify the factors leading to a patient’s development of the disorder. 

Introduction 

Around 5-21% of women in their reproductive age have some form of Polycystic Ovary Syndrome (PCOS) [6]. PCOS is diagnosed using the Rotterdam Criteria [1,5,6]. This considers menstrual dysfunction, presence of ovary morphology through ultrasound, and clinical or biochemical hyperandrogenism [1,3,5,6]. The latter refers to the excess production of androgens, steroid hormones such as testosterone that aid in regulation within male bodies. When viewing ovary morphology through ultrasound, the technician looks for ovaries that contain cysts on the outer layer. More than twelve follicular cysts on one or both ovaries measuring 2-9 mm in diameter provides direct evidence in diagnosing a woman with PCOS [1,3,5]. This narrows down the meaning of PCOS’s name: poly- meaning “many” and -cystic meaning “cysts.” Identifying two of three categories above as a symptom aids in the diagnosis of women with this disorder. PCOS is characterized by low to no ovulation and hyperandrogenism [6], leading to higher testosterone levels and lower estrogen levels. The condition has been shown to lead to multiple lifetime alterations on the body, both internally and externally. It is accompanied by menstrual irregularities, obesity, infertility, hirsutism (excess hair on the chin and mouth) [3,6], and reduced insulin sensitivity [5], making women more susceptible to hypertension, type 2 diabetes, cardiovascular diseases [3], and endometrial cancer [5]. Endometrial cancer is the most common cancer women can develop within their reproductive system; it refers to cancer cells building up along the uterine wall. While PCOS is a fully hormonal condition and not genetic, the causes leading to its diagnosis continue to be under investigation. Within the ongoing research developing in this field, commonly investigated putative causal agents are Endocrine Disrupting Chemicals (EDCs) [1,3,5,6]. These chemicals interfere with the endocrine system’s ability to maintain our homeostasis by mimicking the activity of essential hormones inside the body, blocking their production and secretion. Without proper regulation of those hormones, human development is severely altered or stunted [1,3]. Many suspected EDCs are used widely, and if associated with PCOS, it is important to decrease their use for better alternatives to help decrease the percentage of women developing the syndrome. This review will examine the relationship between PCOS onset and bodily concentrations of one EDC: Bisphenol A (BPA). It will first discuss what BPA is, how the concentrations were found using blood and samples, and finally how this toxin may or may not affect other hormonal parameters. 

What is BPA? 

BPA and its analogs are highly abundant and potent EDCs found throughout the world [1,3,5,6]. Chemically, they are formed using two phenyl rings joined together [6]. This phenyl ring structure is similar to the structure of sex hormones, meaning the chemicals can interact with sex hormone receptors [2]. Analogs are widely used as alternatives to BPA to achieve BPA-free status, but they have been found to exert similar effects [6]. All are hormonally active: through interaction with sex hormone receptors, they can imitate similar dysfunctional effects as the intended hormones, leading to estrogenic, androgenic, and antiestrogenic effects [2]. Exposure to BPA occurs through various forms of contact on skin, inhalation, and consumption of food or water after heating [6]. But why are we using BPA in the first place?  The combination of its ability to increase the durability of polymers and inexpensive access have made it an especially valuable binder and hardener for many, many products.  It’s used in the production of plastics, water containers, hospital equipment, thermal paper, waste water and electronic equipment [1,2,3,5,6]. It’s able to create packages that extend the shelf life of foods and prevent spoilage [4]. It was even added to baby bottles [2,5,6], though it has since been removed from production and use in many countries [6]. As a result, nearly 10 million tons of BPA are produced and 100 tons are released into the atmosphere on a yearly basis [4, 7]. This led BPA to appear everywhere, including in food items like meat, poultry, and dairy products that came from animals exposed to the chemicals [2]. In Europe, unintentional human intake due to this overabundance of BPA rose as high as 50 ug/kg a day. To tackle these concerns, there has been a restriction in the use of BPA in products within the region. Daily intake values fell to 4 ug/kg [2]. While this sounds like a huge success against PCOS, these measures don’t address the similar-behaving analogs replacing BPA. As a result, findings about BPA in this review can extend to such analogs by a degree. With this information, there is minimal material available that can be used as a safer alternative; further research is still required for this topic. 

BPA Concentrations Identified Through Blood 

BPA is identified through urine and blood samples, typically via High Performance Liquid Chromatography (HPLC) with Tandem Mass Spectroscopy [1,2,4,6,7]. HPLC is the process of putting a sample under high pressure and being able to separate, identify, and view the quantity of a substance. Some researchers also measure concentrations using High Performance Gas Chromatography (HPGC), which uses vaporizable chemicals instead [3], or a simple immunoassay (a biochemical test measuring the level of a specific molecule using antibodies) [5]. An immunoassay can be used in tracking hormones in the body and identifying their levels. Using these methods, studies have attempted to identify the connection between BPA concentration levels and hormonal levels within the female body that ultimately lead to the diagnosis of PCOS. 

Multiple studies obtained blood samples from both women diagnosed with PCOS and healthy women with no prior hormonal disorders [1,2,3,4,5]. Each study individually assigned a limit of detection (LOD), the lowest possible value that a sample can contain in order for it to be considered significant. The LODs mostly ranged from 0.009 ng/ml [2,4] to 0.00165 ng/ml [5] but went as high as 0.08 ng/ml [6]. It is important to remember that women with PCOS suffer from menstrual irregularities, meaning their menstrual periods can be absent. Within a specific study, they chose to supply females with dydrogesterone [2], a progesterone oral contraceptive. Progesterone is supplied to women in need of a menstrual period in order to aid in the shedding of their lining, decreasing the possibility of endometrial cancer. On the contrary, Zhou et al. (2016) preferred that women with PCOS had no prior hormonal medications, treatments, or oral contraceptives given to them [7]. This difference can aid in the comparison of results as supplying hormones to women with PCOS can cause a change in the levels overall. 

As blood samples were obtained in both group populations, it was found that BPA concentrations could be identified through all gathered samples. Jurewicz et al. (2021) found that within the women diagnosed, there was a little less than half of an increased amount of BPA concentration found in their blood. The women with PCOS had a mean value of 0.14 ng/ml when looking at BPA concentrations, while the control group had a mean value of 0.8 ng/ml [2]. Kawa et al. (2019) found BPA levels to be significantly higher in women with PCOS than the control groups, a mean of 26.4 ± 14.9 in women with PCOS compared to 18.95 ± 8.8 ng/ml in healthy women. Using a p-value test that considers values below 0.05 to be statistically significant, the BPA concentrations scored a p-value of 0.0046, therefore being significant [3]. Throughout the course of all studies using blood as their preferred method for research, it was consistently found that BPA concentrations were significantly higher in women with PCOS than healthy women; this outcome could be identified in both another study done where dydrogesterone [2] was given and when no prior hormonal contraceptives were given [7].

BPA Concentrations Identified Through Urine 

With a clear correlation between BPA blood concentration and PCOS established, scientists then explored a second diagnostic medium: urine. Some studies have suggested that obtaining urine samples can be a better way of assessing the correlation between EDCs and certain disorders. This is because they are metabolized in the liver and then excreted from the body very quickly [2]. BPA in particular has a half-life of 2-6 hours in the body, which is on the lower side for chemicals. As such, it would make sense that much of one’s BPA exposure ends up in urine. Using a similar framework as the blood tests, these studies obtained urine samples from both population groups and examined them via HPLC and HPGC with set LODs for further identification of BPA levels. These LODs ranged from 0.1 ug/L [7] to 0.08 ng/mL [6]. One study, Akgül et al. (2019), found that women with PCOS had mean BPA urine concentrations of 15.89 ± 1.16 ug/g, compared to a mean 7.3 ± 1.38 ug/g for healthy women. This test scored a p-value of 0.001, thus holding strong statistical significance [1]. In a sample size of 321 women with PCOS and 412 healthy women, Zhan et al. (2023) found that the PCOS subjects had a median of 1.42 ug/g of BPA concentration in their urine creatinine. The median amongst healthy subjects was 0.76 ug/g [6]. However, the study also found traces of other BPA analogs in all subjects, which lends the possibility that higher BPA concentration in PCOS subjects was merely incidental.  To test this, they used an adjusted odds ratio (aOR), which calculates the association between two variables within an experiment with multiple variables. This allows the study to account for potential influence by confounding variables. Zhan et al. (2023) calculated the aOR for a BPA-PCOS association at a 95% confidence interval to be 1.05-1.14, meaning that they found a 95% likelihood that BPA in urine increased the risks of PCOS by anywhere between 5-14% when accounting for analogs.[6]. 

With the aforementioned studies, it would seem that urine research further supports the hypothesis that BPA concentrations in women with PCOS are significantly higher than those of healthy individuals. In reality, there are still disagreements. Zhou et al. (2016) stood out as the outlier of all sources provided. It examined urine samples from 268 healthy women and identified BPA concentrations well above the LOD in all of them, the LOD being 0.1 ng/ml. The median was 2.35 ng/mL [7], highlighting the fact that healthy women can obtain higher BPA concentrations than expected. This points to an area of research that would require further investigation as it marks a significant contrast to other studies’ conclusions. 

BPA’s Association to Hormonal Parameters 

If PCOS is a hormonal disorder, it would be valid to ask whether or not BPA can have a direct correlation with other hormonal parameters. Multiple studies tested the correlation between hormone levels such as testosterone, insulin, progesterone, follicle stimulating hormones (FSH; manages menstrual cycle) [1,2,4,7], and antral follicle count (AFC; number of follicles inside the ovarian reserve) [7] and BPA. Follicles are liquid filled sacs within women’s ovaries that carry immature eggs; through menstrual period stages those eggs become mature and are eventually sent into ovulation. In PCOS, these follicles neither mature nor secrete the necessary hormones needed for menstruation. It was found that all women with PCOS had a significantly higher level of insulin and significantly higher levels of testosterone in their immunoassays [2,4], as expected of the syndrome. Additionally, women with PCOS had a significantly higher FSH ratio, which can indicate an ovary producing too few eggs. While it was clear that women with PCOS had an increased amount of BPA concentrations within their body, it was found to be the opposite for hormonal parameters. There was no statistical significance found when looking at BPA and FSH, indicating an inconclusive relationship between the two variables [1,2,7]. Although there was no connection found between listed hormonal parameters, Zhou et al. (2016) found a correlation with AFC. Using linear regression analysis, an inversely proportional relationship could be seen between BPA concentrations and AFC. This negative correlation was significant, yielding a coefficient (the “slope” of the linear relationship) of -0.32 and p-value of 0.01 [7]. This suggests that exposure to BPA could have a further negative effect on the ovarian reserve within women. Although there was a direct connection between BPA and AFC, no further connections for the hormonal parameters tested were found. 

Conclusion 

With PCOS diagnoses on the rise every year, the need for research in its cause and cure grows ever dire. This review found that concentrations of BPA are significantly higher in women with PCOS through both blood and urine samples. This direct association could help further identify the true cause to why more and more women are developing PCOS. As PCOS is not a genetic disorder, it can be hard to pinpoint the exact cause for diagnosis or development within the female body.  However, ongoing research of EDCs clearly demonstrates their association with the disorder. Being capable of entering the body and mimicking hormone production, EDCs are the most probable causes for PCOS development. BPA is an especially potent culprit due to its near-omnipresence around the world and particular estrogenic mimicry. 

However, the research on what can cause PCOS and what is associated with a diagnosis is far from finished.  The apparent discrepancies that contradict majority findings must be further investigated and research on a broad category of EDCs further expanded before we can say that the relationship between PCOS and EDCs is causal beyond any doubt. Only when this conclusion is reached can we most effectively support women struggling with the debilitating lifelong condition that is PCOS.

About the Author: Angelina Osley

Angelina Osley is a fourth-year Biological Sciences major with an interest in DNA analysis. Her love for all things biology began junior year of high school when introduced to a forensic science class. Since learning about the details of forensic science analysis within a lab she has chosen to pursue a bachelor’s degree in biological sciences to further obtain skills within the lab environment in hopes of one day obtaining a position that helps solve day-to-day crimes. When asked what scientific topic she would like to discuss in further detail it was not hard to know that PCOS was the one for her. After being diagnosed with PCOS at a young age it always weighed heavily on her mind and left her wondering as to what may have caused it. There were days where she felt hopeless and felt like everything always happened to her. Getting diagnosed was one of the biggest moments of her life as PCOS is a lifelong condition, although there are things that diagnose the condition there is still no exact reason as to why it develops. She felt that explaining the condition and potential reasons may help other women understand it and potentially realize that some symptoms being experienced are PCOS.

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