Los consumidores modernos están constantemente inundados de advertencias de productos químicos nocivos en productos cotidianos. Es tan común que estas advertencias sean falsificadas o exageradas que encontrar el peligro en químicos inofensivos casi se ha convertido en cliché. Desafortunadamente, estas advertencias distraen la atención de los informes sobre sustancias químicas que en realidad podrían causar daños. Uno de estos químicos nocivos omnipresentes es el bisfenol A (BPA).
BPA es un componente crítico de la fabricación de plástico y epoxi, lo que significa que está en una variedad de productos, incluso aquellos que usted no esperaría. para encontrar cualquier plástico, como empastes dentales y latas de aluminio. Estas latas están revestidas con una variedad de materiales, incluidos plásticos y epóxicos, que evitan que el contenido líquido degrade o oxide el aluminio de la lata.
El BPA en revestimientos de latas es un análogo de estrógenos, lo que significa que puede interferir con la señalización hormonal. La mayoría de la gente normalmente piensa en el estrógeno como una hormona relacionada con las características sexuales secundarias y la fertilidad, pero también está involucrado en muchos otros procesos, como función hepática y respuesta a la insulina. En consecuencia, los investigadores han comenzado a estudiar los efectos del BPA en diversos parámetros de salud. Como era de esperar, el foco principal de la investigación inicial fue sobre los efectos del BPA en la fertilidad, especialmente a la luz del hecho de que la contaminación ambiental del BPA en general perjudica la reproducción y el desarrollo de los animales .
A medida que el campo madura, sin embargo, los investigadores están comenzando a evaluar una variedad de otros parámetros de salud que podrían verse afectados por el BPA (como se ve en la Figura 1), incluida la presión arterial. Algunos estudios previos han demostrado una correlación entre el consumo de bebidas enlatadas o la exposición al BPA y la hipertensión, pero hay muy pocos estudios para evaluar si la exposición al BPA provoca cambios en la presión arterial. Este estudio fue un seguimiento del trabajo previo realizado por los autores. Específicamente, buscó determinar si la exposición al BPA del consumo de bebidas enlatadas podría afectar la presión arterial.
BPA, un componente de la fabricación de plásticos y epoxi, se encuentra en el revestimiento de las latas de bebidas y muchos otros productos. Es un análogo de estrógeno y puede causar una variedad de problemas de salud. Los autores de este estudio examinaron si el BPA puede afectar la presión sanguínea.
Los participantes en este estudio fueron 60 personas mayores, pero por lo demás relativamente sanas. Casi todos los participantes eran mujeres. Alrededor de la mitad de ellos informaron antecedentes médicos de hipertensión o diabetes, y la mayoría de los participantes que informaron estas afecciones estaban recibiendo tratamiento para ellos en el momento del estudio. Los investigadores seleccionaron específicamente participantes de edad avanzada porque es más probable que se vean afectados por la exposición a sustancias químicas ambientales que los adultos jóvenes y de mediana edad. Los participantes bebieron dos porciones de leche de soya de botellas de vidrio o latas de aluminio. La leche de soja proviene del mismo fabricante que ofrece dos opciones de envasado diferentes: una botella de vidrio sin BPA o una lata de aluminio que contiene BPA.
Los participantes ayunaron durante ocho horas, llegaron al sitio de estudio, bebieron dos porciones de leche de soja de un recipiente elegido al azar, y se analizaron dos horas más tarde. Debido a que ambas porciones fueron aleatorizadas, los participantes recibieron dos porciones embotelladas, dos porciones enlatadas o una porción enlatada y una porción embotellada. Los análisis consistieron en pruebas de orina altamente sensibles para la concentración de BPA, evaluaciones duplicadas de la presión sanguínea en reposo tomadas con una separación de aproximadamente 10 minutos y monitorización de la variabilidad de la frecuencia cardíaca.
Is there evidence for heart rate variability?
Heart rate variability (HRV) has recently gained more attention in popular media, but it has shown associations with health outcomes for many years. Most of the original research on HRV was done in the context of heart attack risk and mortality. More recent studies have focused on the interaction between HRV and other parameters beyond cardiac functions. Associations between HRV and a variety of processes, including factors like concentration, have been noted, and the field is rapidly expanding. HRV monitoring has also become a popular tool for athletes to assess whether or not they are over-reaching, because it is believed that HRV can be used as a barometer for overall bodily stress. But so far, the scientific evidence behind this claim isn’t so strong.
The researchers performed the same procedure three separate times with a week in between each visit. In each visit, the researchers randomized the participants to another group, so every participant eventually consumed soy milk from all three possible packaging combinations. This crossover design ensured that any demographic differences between the groups canceled each other out because every participant had a data point in every experimental group, which means it takes fewer overall participants to notice any effects. This is a key feature of crossover studies and one of the reasons they are regarded as very reliable.
The researchers also used very stringent statistical analyses to ensure that blood pressure measurements were standardized for all environmental factors, including climate and nonexperimental BPA exposure.
The experiment consisted of giving healthy, elderly participants soy milk to drink either from two bottles, two cans, or one bottle and one can in a crossover design, where each participant participated in each condition. Researchers measured the blood pressure and urinary BPA concentration of each participant.
Urinary BPA concentration increased significantly only in participants who consumed soy milk from aluminum cans. After accounting for environmental factors, blood pressure increased linearly with urinary BPA. Participants who consumed two servings from the cans showed roughly a five mmHg increase in systolic blood pressure compared to those who consumed two servings from bottles. The change in systolic blood pressure was significant between groups both with and without extensive statistical adjustment, whereas there was no significant change in diastolic blood pressure.
Despite the significant changes in blood pressure, heart rate variability did not change. This is in contrast to the researchers’ previous study, which found that heart rate variability significantly decreased (and blood pressure increased) in a much larger cohort of patients. Decreased heart rate variability is associated with a variety of negative health outcomes, including mortality after heart attacks.
BPA was associated with an increase in systolic blood pressure, but not with changes in heart rate variability.
BPA exposure acutely increases blood pressure in elderly women. One canned drink serving is sufficient to significantly increase BPA concentrations in the body, while two canned drink servings causes a transient, measurable blood pressure effect.
It can be implied that a substantial amount of BPA leached from the can liners and into the canned beverages. This suggests that the consumption of canned beverages (depending on the BPA content of the packaging) will not only increase the BPA concentration in the body, but also have measurable, negative effects on blood pressure. Drinking the same beverage from a BPA-free glass bottle does not result in this response.
The researchers used soy milk rather than water. They note that soy milk hasn’t been found to increase blood pressure and is widely commercially available, and is hence an ideal study beverage. While they cited longitudinal and trial evidence of soy milk actually decreasing blood pressure, that evidence doesn’t really apply to the current study because it doesn’t look at acute blood pressure changes, occurring right after beverage consumption.
Given that soy phytoestrogens have some estrogenic activity and that soy milk contains fat (which could theoretically increase the extraction and solubility of fat-soluble compounds such as BPA from the liner), soy might not actually be the ideal study beverage. Interestingly, even the soy milk in the glass bottles had a bit of BPA in it (with levels at 0.31 and 8.2 μg/L, in bottles and cans respectively.) As shown in Figure 2, heat exposure and age of packaging can affect BPA levels, so there are other factors to consider outside of simply the beverage and type of packaging material. It would be worth replicating this trial with water, soda, and other common beverages, to see if the results are similar.
This study is in line with previous studies that found significant biological changes in response to acute BPA exposure. Some of these previous studies were conducted by the same group that conducted this study. This study is still important, however, because it confirmed many previous correlative findings from a variety of groups. More importantly, it also suggests a direct causative role for BPA increasing systolic blood pressure: participants experienced a small, but significant, increase in blood pressure after consuming a canned beverage, and this blood pressure increase appeared to correlate with an increase in urinary BPA.
Despite the fact that this study showed that BPA exposure can cause acute blood pressure changes, it is still not clear how chronic BPA consumption affects health outcomes. It is important to avoid extrapolating biological changes to disease states. This is one of the most common errors in science journalism. Practically speaking, this means that a small transient increase in blood pressure may not necessarily cause hypertension or other chronic diseases in the long run. BPA exposure might have a clinically relevant effect on blood pressure in some cases (for example, increasing the blood pressure of a prehypertensive person into the hypertensive range for a few hours), but it is not clear how long the response to BPA lasts. Much more work needs to be done before can-based exposure to BPA can definitively be linked to a disease state like hypertension or cardiovascular disease. If this link is eventually found, it would be a major finding, but it would also make it difficult to conduct further studies on BPA because ethical review boards are unlikely to approve studies that involve exposing participants to chemicals with known harmful effects.
Another factor to keep in mind is that many of the participants in this study were already being treated for hypertension. There is always a risk for confounding factors when a large subset of a study population is known to have aberrations in a measured variable. Consequently, a similar study in a different population could have different results. The findings of this study are likely real, but they may be population-specific. For example, younger participants with normal blood pressure values could respond very differently to BPA, and BPA may interact with anti-hypertensive medication in some unknown way. Therefore, other studies to specifically assess the mechanisms linking BPA and blood pressure are needed to conclusively say how BPA causes these effects.
Even in this study, the researchers were uncertain as to how exactly BPA increased blood pressure. The effect may have been due to estrogen receptors (which can play a role in blood vessel repair, although that may more of a role in longer term blood pressure impacts), thyroid hormone effects, or mechanisms that haven’t yet been well-elucidated.
If BPA is ubiquitous, what’s the point in avoiding it?
Because BPA seems to have dose-dependent effects, it’s still likely useful to minimize BPA exposure whenever possible. Many correlative studies, some of which used extremely large data sets, have found associations between BPA exposure and a variety of cardiovascular disease states, including heart attacks.
However, there isn’t much evidence for direct interactions between BPA exposure and health risks in humans. There is, however, a large body of evidence studying the effects of BPA exposure in a variety of animals, and which typically show harm. At this point, minimizing BPA exposure is a good idea, since a policy-level intervention like banning BPA from all food products isn’t so likely, at least in the US (in contrast, France has much stricter policies, with regulations starting in 2015). This may be due to huge economic ramifications and lack of feasible alternatives for all of BPA’s many uses.
Why don’t manufacturers move away from BPA if there’s so much data suggesting against its use?
It would be very expensive to convert machinery and processes from standard procedures to BPA-free alternatives. More importantly though, such a conversion likely wouldn’t increase sales enough to offset the expense. Because there’s no government regulation and no definitive proof that BPA causes medically relevant harm, it’s far easier and more economical for large companies to maintain their current manufacturing and packaging processes. One example is store receipts. As seen in Figure 3, many receipts contain fairly large amounts of BPA. This may be a concern for those who repeatedly handle store receipts (such as clerks or shopaholics), and the effect is amplified when hand sanitizer or certain lotions are worn. Despite the public outcry in 2010, when the data was released, few stores have turned to alternatives.
However, many niche and small manufacturers, especially those in the health and wellness community, have moved to BPA-free processes. Therefore, these BPA-free products may be good alternatives as the growing body of research on BPA’s negative effects pushes consumers toward BPA-free products
Why is there so much research on BPA?
BPA is an estrogen analogue, which means it can bind to estrogen receptors in the body. Estrogen is a nearly ubiquitous signaling hormone in the animal kingdom, and it is responsible for many things beyond the secondary sexual characteristics it is normally associated with. Estrogen receptors are found on nearly every major tissue type in the human body, and they are key regulators of processes including bowel motility, fluid balance, blood coagulation, and metabolic health.
It is also similarly important in most animals, some of which are far more sensitive to endocrine disruption than humans. Fish and other aquatic species are especially susceptible to BPA exposure, and because it causes a variety of birth defects in these species, it is believed (with a growing body of supporting evidence) that it may also affect human cellular and metabolic signaling.
BPA is nearly ubiquitous, but it should still be avoided when possible, which means avoiding canned beverages and trying to find containers that are BPA-free.
The findings in this study are mostly applicable to elderly women, but the entire body of research on BPA exposure seems to indicate that BPA offers no known health benefits while being associated with a variety of potential health risks. Unfortunately, BPA is everywhere, which makes avoiding it very difficult. However, it is also important to realize that although there are many correlations between BPA and disease states, as well as some direct evidence that BPA causes acute biological and metabolic changes, there still isn’t enough evidence to say whether or not BPA actually directly contributes to disease. If it does, it’s nearly impossible to quantify the exact contribution to disease, as it’s one single part of a multifactorial disease process. Since the evidence for health impacts will never be ideal, it’s a personal decision as to how much you want to focus on BPA-reduction in everyday life.