How Microplastics Are Related to Dementia – Conversations to Remember

How much of your food comes in plastic containers? What about the environment – how much plastic is circulating in there? Now, imagine all those plastic particles being absorbed in the human body. What then? This phenomenon is raising new concern as scientists are trying to uncover what small plastics do to the body, namely microplastics and nanoplastics. Microplastics are less than 5 millimeters in diameter as a result of being manufactured or broken down by elemental factors. Nanoplastics are less than 1 micrometer in length, meaning they pose greater risks than microplastics and can disperse more rapidly across the body. Despite their differences, both types of plastic are virtually invisible to the naked eye.

Microplastics are practically everywhere on Earth, and in various species, both on land and in the sea. To demonstrate their abundance, scientists have found microplastics from the depths of the Mariana Trench to the heights of Mount Everest. It is speculated that these tiny substances enter our bodies when we consume items that are encased in plastic (e.g., water from plastic bottles) or when we inhale the substances from our environments (e.g., degradation of synthetic material). Microplastics can also penetrate the skin, such as through direct contact with clothing or cosmetic materials. Animals are no strangers to microplastic consumption, either, as they are similarly exposed via their environment and/or diet. Such findings demonstrate how much of a global issue this is and how common microplastics are.

Humans and animals can get introduced to microplastics through sewage and agricultural systems. As we wash products that contain microplastics in our sinks or washing machines, these small particles can easily transfer from our sewers to our soil, which already has a concerning amount of microplastics. Consequently, the produce we and animals consume can be coated with microplastics, which can enter our digestive tracts. This plastic exposure is so frequent that a study in the Netherlands reported that 75% of their beef and pork products found in supermarkets and farms contained microplastics. Fish are no exception, either, as many studies have found microplastics in their muscle and gut due to sewage systems transfering microplastics to the ocean.

Aside from being in our environments, microplastics are also in our bodies. In recent studies, scientists have found microplastics in various locations of the human body, including the lungs, testicles, liver, kidneys, blood, brain, placenta tissues, and breast milk. This means that we can be exposed to microplastics even before we are born. On average, scientists predict that we annually consume 78,000 and 211,000 microplastic particles. As we age, the body experiences a harder time filtering out these toxins as it physiologically declines. Ultimately, this accumulation of microplastics can lead to an increase in organ damage, oxidative stress, and genotoxicity over time. Oxidative stress is a neurotoxin that occurs when we have more unstable and highly reactive molecules (i.e., free radicals) in the body compared to protective cell substances (i.e., antioxidants). When this happens, our metabolic pathways can be harmed. One example of this is genotoxicity, which is delineated by neuroinflammation and DNA damage. Genotoxicity can result in our genetic makeup becoming so altered that it could lead to negative genetic mutations.

Even though our understanding of microplastics is still in its preliminary stages, especially with regards to its long-term effects, current research suggests that their accumulation in the human body is linked to a plethora of health conditions. One of the illnesses microplastics is connected with is dementia. Dementia is a neurodegenerative disease that is characterized by a gradual decline in memory and cognition. People living with dementia reportedly have an increased risk of accumulating more microplastics within their brain compared to those who do not have the condition; the amount of risk is currently uncertain as some sources suggest that it could be three to fives times while others infer it is ten times. The brain is most vulnerable to these effects as it harbors the highest rates of microplastics compared to any other organ in the human body. This finding is so prevalent that recent reports suggest that the average human brain contains a spoonful of microplastics, and has seven to thirty times more of these substances compared to vital organs, such as the kidneys and liver. For that reason, many tend to dub microplastics as “plastic pollution” for the brain. The most common type of microplastic found in the brain is polyethylene, which is commonly present in packaging materials, plastic bags, cups, bottles, insulation equipment, and water pipes.

Scientists hypothesize microplastics can travel to the brain via the bloodstream, and are highly attracted to its lipid-composition. This is because microplastics are hydrophobic (i.e., repel water), meaning they are drawn to other hydrophobic materials, like lipids. Once inside, microplastics can remain in the brain for an extended period of time before completely disintegrating, especially since dementia causes the brain to have impaired clearance properties and alters its shape and volume. In healthy individuals, the brain naturally begins to experience changes in its size. However, during dementia, the brain starts to shrink at a faster rate as its cells (i.e., neurons) start to die off; this process is known as brain atrophy. When this happens, the brain will have more available pockets for microplastics to accumulate in over time.

What makes plastics so much more damaging for the brain are nanoplastics, which, as mentioned earlier, are smaller than microplastics. This means that they have the potential of bypassing the blood-brain-barrier (BBB), and entering the brain. Under normal circumstances, the BBB is critical for preventing toxic materials from entering the brain, as it insulates the brain’s tissues with a layer of protective cells. However, when inflammation, which commonly happens when microplastic levels increase, or chronic brain conditions (e.g., dementia) occur, our BBB’s selectively permeable membrane weakens, which can lead to a higher potential of allowing harmful substances to enter the brain.

With all this information, it is important to note that scientists are not currently claiming that micro- or nanoplastics are causing dementia. There is simply not enough evidence to make such a definitive remark, especially as the study of plastic permeability is still in its infancy. Instead, contemporary research merely suggests that there is a correlation between plastic exposure and negative brain health outcomes, which should be further examined. This call for more research is supported by the current literature acknowledging a consistent, global uptick in plastic consumption in recent times compared to years prior. For that reason, we need to encourage more research studies to gather data on this ambiguous relationship between microplastic exposure and dementia.

Scientific studies are already being performed on animal subjects, such as in murine research labs. In one neuroscience study, mice were exposed to microplastics for three weeks. At the end of the experiment, the mice started displaying cognitive decline symptoms similar to dementia, as the microplastics breached their BBB and entered their brains. Even though this study offers critical insights, scientists cannot yet use its findings to claim that microplastics cause dementia as further research needs to replicate the findings and generalize them to human populations. Nevertheless, its results still strongly support the notion that microplastics’ effects are not benign; instead, they are apparent and deserve to be investigated further. In turn, this research can allow scientists to concretely determine if there are any causal explanations between dementia and microplastics in the future.

Present-day researchers have compiled a list of recommendations for reducing microplastic consumption. One suggestion is to limit our plastic utilization by opting for reusable appliances and lessening our single-use plastic choices. For example, instead of purchasing a plastic water bottle, we could use reusable alternatives (e.g., glass or stainless steel) and a filtering system for our tap water. Doing this could reduce our exposure by 90%, as it lessens our annual microplastic consumption from 90,000 to 4,000 particles. Another recommendation is to select clothes with natural fibers (e.g., cotton) rather than synthetic (e.g., polyester) ones that tend to release microplastics in the wash. Additionally, it is important to frequently vacuum and/or sweep the area to limit the amount of dust and debris. This is because microplastics are airborne in indoor settings, and can enter our nasal cavity whenever we inhale. Opening windows to let outdoor air enter and using air purifiers can further assist with preventing the accumulation of microplastics in our environment. Lastly, we should try to reduce how many times we heat food up in plastic containers, especially in microwaves. Such materials can make their way into the foods we eat, which can then enter our bloodstream and negatively affect our vital organs after consumption.

A final piece of advice that researchers advocate for is for us to petition our government agencies and manufacturers to limit our plastic production and use safer alternatives whenever possible. There is no way we can completely escape plastic exposure, as it is used in a variety of settings due to its durability, versatility, cheap manufacturing, and low-weight composition. For that reason, we should try to work as a collective to push for policy change that can bring more attention to this issue, and generate new funds and grants for research in this area to better understand how plastics can impact our health for years to come.

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