And I want to talk about this now. So there's a potential link between BPA and autism spectrum disorder. There are multiple human observational studies that suggest a connection between maternal BPA levels and an increased risk of neurodevelopmental disorders, including autism spectrum disorder. For example, one study from Harvard School of Public Health found that higher BPA levels in pregnant women were associated with behavioral problems in their children, particularly boys. So these included issues like anxiety, aggression, impaired social functioning. These are traits that overlap with autism spectrum disorder symptoms.

Another large cohort study followed pregnant women and their children over several years and found that higher maternal BPA exposure during pregnancy was associated with poor neurodevelopmental outcomes in children, including several behavioral problems. And again, these effects were more pronounced in boys. While the study didn't specifically diagnose autism. The behavioral impacts they observed align again with traits that are seen in autism spectrum disorder. There's also a meta-analysis that reviewed several studies on maternal BPA exposure and neurodevelopment.

And although it didn't conclusively prove a direct link to autism, it did find consistent evidence that prenatal BPA exposure increased the risk of behavioral issues like hyperactivity and inattention, which are common in children with autism spectrum disorder and also other neurodevelopmental disorders. And when you pair that with the animal data, it becomes harder to ignore this potential connection. Animal studies have consistently shown that BPA exposure during pregnancy causes offspring to have deficits in social behaviors, increased anxiety, and altered brain structure in key areas like the prefrontal cortex and hippocampus, the same brain areas that's affected in humans with autism. And it's not just about BPA exposure during pregnancy. There's actually another layer to this.

So one study found that children Children with autism spectrum disorder actually struggle to metabolize BPA, so their bodies aren't detoxifying the chemical as efficiently, so it builds up, especially in its active form, free BPA, which means it's circulating in their systems longer and potentially affecting brain development throughout childhood and adolescence. This is important because estrogen receptors in the brain play a key role in things like cognition, memory, social behavior, areas that are often impacted in autism. Some research actually suspect that this impaired metabolism of BPA in kids with autism spectrum disorder could be disrupting those key neural pathways, which could explain some of the cognitive and behavioral challenges that are seen in autism.

It's almost like this one-two punch. First, you've got maternal exposure during pregnancy, which affects the structure and development of the brain. Then if that child is less able to metabolize BPA efficiently, it sets up this prolonged exposure to a chemical that's known to interfere with brain development. So animal studies consistently show that early life exposure to BPA disrupts neuronal circuits responsible for learning, attention, behavior. And this could explain some of the cognitive and social deficits seen in children with autism spectrum disorder. But the effects of BPA on the developing brain don't end with autism. There's also evidence that prenatal exposure to BPA is linked to a higher risk of behavioral problems like anxiety, attention disorders, and even ADHD.

So a study published in 2017 found that kids who were exposed to higher levels of BPA during pregnancy were more likely to develop ADHD along with anxiety and depression later in childhood. So how does BPA do all this damage? Well, it seems like it interferes with the key neurotransmitter systems, specifically dopamine, and serotonin that affect brain function. So these, these chemicals are crucial for regulating mood, attention, cognitive function. And during development, serotonin actually plays a key role in shaping the structure and function of the brain. It's actually called a brain morphogen during development. So it's shaping the growth and differentiation of neurons during early life.

It acts as a growth factor during embryonic development, influencing the development of key brain regions like the cerebellum by promoting dendritic growth and synapse formation and stabilization. These are critical processes for proper neural circuit formation and coordination between brain regions. Disruption of the serotonin system during this very critical period could absolutely affect brain development. In fact, vitamin D deficiency during pregnancy may also disrupt serotonin production, which could affect autism risk. I actually published 2 studies on this very topic a few years ago.

So the fact that BPA is linked to autism and it disrupts the serotonin system, and vitamin D deficiency also is linked to autism during pregnancy and also disrupts the serotonin system, to me strengthens the connection. Because when you start to see different environmental factors that are all sort of aligning and converging on a similar mechanism, it's really hard to ignore. So on top of that, BPA also induces oxidative stress in the brain. So this means it's generating harmful free radicals that damage brain cells. It impairs their ability to communicate and to adapt. This is what we call synaptic plasticity. That oxidative stress can also trigger inflammation, which just sort of amplifies the damage, especially in developing neurons.

Now I want to get onto something that we touched on earlier in the podcast that also is pretty concerning. And it's the idea that microplastics could actually be making their way into the adult brain. So when we think about how the body protects the brain, we usually think of the blood-brain barrier. This is a highly selective shield that's supposed to keep harmful substances out of the brain. But there's emerging evidence suggesting that microplastics, especially the smaller nanoplastics— so these are less than 1 micrometer— can actually cross the blood-brain barrier. And once they're in, they could cause some real damage. For example, one study found that polystyrene microplastics were accumulating in critical brain regions like the hippocampus and the prefrontal cortex.

These are areas responsible for memory, for learning, for emotional regulation. When these microplastics settle into brain tissue, they can trigger an inflammatory response. They spike levels of pro-inflammatory cytokines like TNF-alpha, IL-6. These are markers that are associated with chronic brain inflammation, and we know chronic brain inflammation is linked to neurodegenerative diseases like Alzheimer's disease, like Parkinson's disease, and even just normal cognitive decline. If you want to learn more on how neuroinflammation plays a major role in the development of neurodegenerative disease, please check out my previous episode, episode number 79, with Dr. Axel Montagne on the blood-brain barrier and Alzheimer's disease.

And it's not just animal studies that are showing this connection. There's emerging human data showing accumulation of microplastics in brain samples taken from human autopsies. In one study, researchers examined tissues from livers, kidneys, and brains of autopsied individuals. While all organs contained microplastics, the brain samples were particularly concerning because, on average, the 91 brain samples studied contained 10 to 20 times more plastic than the other organs. And these findings are even more disturbing when you consider their implications for neurodegenerative diseases. Among the brain samples studied, 12 were from individuals who had died with dementia, including Alzheimer's disease.

These samples contained up to ten times more plastic by weight compared to those people who had plastics in their brains without dementia. While this doesn't yet prove causation, I think the correlation is enough to raise serious concerns about the role of microplastics in cognitive decline and diseases like Alzheimer's disease. What's also striking is the increase in microplastic concentrations over time. So human brain samples from 2024 had about 50% more plastic than similar samples dating back to 2016. This trend mirrors the rising level of microplastics found in the environment, suggesting that as our environmental plastic pollution increases, so does the plastic accumulation in human tissues like the brain.

So the question becomes, what does long-term, low-dose exposure look like for humans, especially in urban environments where microplastic air pollution is high? And what about kids? So we already discussed this somewhat. During early development, the blood-brain barrier is even more permeable, which means that pregnant women and young children could be at a greater risk for neurodevelopmental issues like autism or ADHD if exposed to microplastics. And observational evidence seems to suggest that this is the case for chemicals associated with them as well, like BPA. So the implications are that we could be looking at higher risk of neurodegenerative diseases, cognitive impairments, and even neurodevelopmental issues if exposure starts early in life. This is something we absolutely need more research on, but the early signs are not good.