The Gut-Brain-Liver-Eye Axis: A Central Communication Network
1. Gut-Eye Axis: Microbial Metabolites as Key Players in Ocular Health
The gut microbiota, or the community of bacteria living in your digestive system, is traditionally known for helping with digestion and nutrient absorption. However, its influence goes far beyond the gut and reaches other parts of the body, including the eyes. One of the ways this happens is through substances called microbial metabolites, specifically short-chain fatty acids (SCFAs), such as butyrate. These are produced by gut bacteria like Faecalibacterium prausnitzii and Roseburia spp. Butyrate has anti-inflammatory effects, which means it helps reduce inflammation, not only in the gut but also in other parts of the body, including the eyes.
A study by Nguyen et al. (2024) from Mercer University and Augusta University, USA, highlighted that butyrate helps maintain the strength of the gut barrier (the lining that keeps harmful substances out of your bloodstream) and reduces inflammation throughout the body. By keeping inflammation in check, it can lower the risk of eye diseases like glaucoma and age-related macular degeneration (AMD)—two conditions that are partly driven by inflammation. Glaucoma is a disease where the pressure inside the eye damages the optic nerve, leading to vision loss. AMD is a condition that affects the central part of the retina, leading to blurred or lost vision, usually in older adults.
The Impact of Gut Dysbiosis
An imbalance in the gut microbiota, known as dysbiosis, can lead to systemic inflammation and increased gut permeability—a condition often referred to as "leaky gut syndrome." When the gut barrier becomes compromised, toxins and bacterial metabolites enter the bloodstream, triggering widespread inflammation. This systemic inflammation may provoke autoimmune responses, as seen in conditions like Sjögren's syndrome (SS). SS is an autoimmune disorder where the immune system attacks the body's moisture-producing glands, causing dry eyes, among other symptoms.
Research, including that of Jayoon Moon and colleagues, has demonstrated that SS patients frequently exhibit gut dysbiosis, particularly with a decrease in the Firmicutes/Bacteroidetes ratio and reduced levels of Faecalibacterium—one of the key producers of butyrate. This microbial imbalance further underscores the "gut dysbiosis–ocular surface–lacrimal gland axis," highlighting the interplay between the gut microbiota and the development of autoimmune dry eye conditions. By addressing dysbiosis—through interventions like prebiotics and probiotics that promote healthy levels of Faecalibacterium—we may be able to alleviate systemic inflammation and improve symptoms of SS, illustrating the vital connection between gut and eye health.
Immune Cells in Eye Health
Building on this connection between the gut and the eyes, a 2023 study published in Science Translational Medicine found that immune cells originating in the gut, particularly β7+ CD4+ T cells, can damage retinal cells in the eye, especially in glaucoma. Gut dysbiosis can lead to the activation of these immune cells, which send distorted signals to the brain, resulting in inflammation that exacerbates eye diseases like AMD and glaucoma. Among these immune cells, T-helper cells (Th cells)—specifically Th17 cells—play a critical role. In cases of gut dysbiosis, Th17 cells can become overactive and cross into the eyes, causing inflammation that damages the optic nerve and leads to vision loss.
2. Brain-Eye Axis: Cognitive and Neurological Impacts on Vision
Just as the gut influences the eyes through microbial metabolites and immune signaling, the brain's immune system plays a crucial role in maintaining eye health. Recent research has revealed a direct connection between the immune responses in the brain and those in the eye, emphasizing how deeply interconnected these systems are. The eye has its own lymphatic system—tiny vessels that manage immune responses—which is linked to the brain via the optic nerve. This connection means that immune activity in the eye can directly affect the brain, and vice versa, highlighting the intricate nature of the brain-eye axis.
Eye Signals Protecting the Brain
One of the most fascinating insights is how immune signals from the eye can actually protect the brain from infections and diseases. For example, studies involving mice demonstrated that immune-boosting treatments administered to the eyes not only preserved their vision but also shielded the brain from infections and aggressive tumors like glioblastoma, a fast-growing type of brain cancer. This research suggests that enhancing immune function in one part of the body, such as the eyes, may have far-reaching effects on other organs, like the brain, opening up possibilities for dual-targeted treatments that benefit both eye and brain health.
Lymphatics Linking Eye and Brain
In groundbreaking research by Eric Song and colleagues (2024), the eye's lymphatic system was shown to play a critical role in immune responses, directly linking the eye and brain. The lymphatic system is traditionally known as the body’s drainage and immune defense network, transporting lymph fluid and immune cells to remove waste and fight infections. While its role in the eye had been underexplored, Song’s research uncovered a distinct lymphatic drainage system in the posterior part of the eye, which connects to the brain via pathways in the optic nerve. This finding demonstrates how immune activity in the eye can help protect the brain from infections and tumors, such as glioblastoma, and opens up new therapeutic avenues for treating diseases that affect both the eye and brain.
Implications for Eye-Brain Disorders
The discovery of this eye-brain immune connection has profound implications for understanding diseases that involve both organs, such as glaucoma, multiple sclerosis, and even Alzheimer's disease. It is now understood that immune cells can travel from the eye to the brain, activating protective responses. This insight is particularly relevant in the case of viral infections like herpes simplex virus (HSV), which can affect both the eye and the brain. Strengthening immunity in the eye through targeted treatments may offer protection against these infections in the brain as well, highlighting the potential for innovative therapies that address both eye and neurological health.
3. Liver-Eye Axis: Nutrient Processing, Circulation, and Inflammation
The liver plays a crucial role in maintaining eye health, regulating blood flow, and processing essential nutrients that support vision. Liver problems—whether due to fat buildup in the liver (non-alcoholic fatty liver disease, or NAFLD), advanced liver scarring (cirrhosis), or inflammation from infections like hepatitis—can lead to vision issues, such as blurred vision, cataracts, or even vision loss in severe cases. For example, disruptions in liver function, particularly in how the liver handles bile acids and sugar levels, have been shown to affect the eyes.
Bile Acids and Inflammation
Another important discovery involves bile acids, which are produced by the liver and help digest fats. These acids also play a role in controlling inflammation in the body, including the eyes. This connection highlights how liver function directly impacts both gut and eye health. When the liver doesn’t properly regulate bile acids or other fat-related processes, it can contribute to inflammation that affects vision.
Intraocular Pressure and Vitamin D
A 2023 study led by Junhao Wu highlights how people with NAFLD are more likely to have higher pressure inside the eye, known as intraocular pressure (IOP). When this pressure increases, it can damage the optic nerve, leading to glaucoma, a disease that can cause blindness. Another important factor is vitamin D, which is often low in people with NAFLD. Low vitamin D levels are linked to increased eye pressure, so addressing this deficiency could help reduce the risk of glaucoma. Since vitamin D made by the skin needs to be processed by the liver and kidneys before it can be used by the body, the liver’s role in making active vitamin D highlights how critical it is to both overall and eye health. Additionally, liver damage, like severe scarring (fibrosis), has been shown to cause changes in the retinal blood vessels, which further connects liver health to eye function.
Nutrients for Eye Health
The liver is also responsible for storing and processing several key vitamins and minerals that protect the eyes. These include vitamins A, C, and E, as well as beta-carotene and minerals like zinc and selenium. These nutrients help prevent damage to the eyes by reducing oxidative stress (which can harm cells) and support the health of the retina. For instance, vitamin A is needed to make rhodopsin, a pigment in the eyes that helps us see in low light. Zinc helps with this process and also supports liver function. Selenium and vitamin E act as antioxidants, protecting both liver and eye tissues from damage.
This connection between nutrient balance and eye health matches findings that deficiencies in liver-stored, fat-soluble vitamins, such as vitamins A, D, E, and K, can contribute to conditions such as glaucoma, emphasizing the liver’s important role in keeping the eyes healthy. For those at risk, maintaining a diet rich in these nutrients or considering a multivitamin and mineral supplement could support both liver and eye health by ensuring adequate levels of these protective vitamins and minerals.
East Meets West: The Liver's Expanded Roles
In both Traditional Chinese Medicine (TCM) and Western medicine, the liver is a vital organ, albeit with different scopes of interpretation. In TCM, the liver is seen as a broader system connected to various bodily functions, particularly eye health. The liver's role in TCM goes beyond metabolism, encompassing emotional regulation and blood storage, all of which impact ocular health.
According to TCM principles, liver blood is essential for proper eye function. When liver function is disrupted, it can lead to visual disturbances. This concept aligns with modern research showing that metabolic and immune disruptions in the liver can lead to ocular diseases. For instance, studies in TCM have long associated liver imbalances with conditions like dry eyes and blurred vision, ideas that find parallels in Western medicine's understanding of the liver’s role in vitamin A metabolism and bile acid regulation.
Both TCM and Western medicine also recognize the impact of stress on liver function. In TCM, stress can stagnate liver qi, leading to symptoms like headaches, irritability, and visual disturbances, including glaucoma. This mirrors modern scientific understanding, where chronic stress and gut dysbiosis affect the gut-liver-brain axis, causing systemic inflammation that impacts eye health. The parallels between these two medical paradigms highlight the liver’s influence on overall well-being, especially in terms of eye health.
In TCM, the liver is symbolized by the color green, associated with renewal and growth. Green is believed to calm and balance liver energy, supporting both physical and emotional health. From a Western perspective, the color green is also linked to health through chlorophyll, the green pigment found in plants. Chlorophyll plays a key role in detoxification and supports liver function, aligning with botanical therapies aimed at cleansing and rejuvenating the body. The synergy between the healing power of green—both metaphorically in TCM and literally in plant-based medicine—underscores the liver’s importance in maintaining health across cultures.
Conclusion: The Interconnectedness of the Gut-Liver-Brain-Eye Axis
The emerging understanding of the gut-eye, brain-eye, and liver-eye axes underscores the profound interconnectivity of our organs. Microbial metabolites like butyrate, bile acids, and immune regulation play central roles in maintaining eye health, while disruptions in the gut, liver, or brain can manifest as ocular diseases. This holistic approach, supported by both modern scientific research and traditional practices like TCM, highlights the need for integrated strategies to maintain health across systems.
Holistic Interconnectivity
When viewed through the broader lens of the gut-liver-brain-eye axis, this discovery reinforces the idea that our organs are not isolated. Just as the gut microbiome influences brain health through immune signaling, the eye’s immune system can also affect brain function. Maintaining healthy immune responses in each of these organs could protect not just one area, like the eyes, but overall systemic health. This holistic view of interconnected body systems could change the way we approach treatment for a wide range of conditions, emphasizing the importance of balance in maintaining wellness.
The interconnectedness of the gut, liver, brain, and eyes highlights how maintaining the health of one organ system supports the others. By maintaining a balanced gut microbiome, supporting liver function, and managing brain health, you’re also safeguarding your vision and overall well-being.
To support the balance of the gut-brain-liver axis, incorporating targeted supplements and lifestyle changes can make a significant impact. For more information, check out these recommended supplements and explore 10 simple steps to reset the axis for optimal health.
Return to:
Let’s begin by exploring the well-known gut-brain-liver axis, a critical communication network that now includes the eyes. These organs work together, maintaining the body’s balance through interconnected signals and responses:
The Gut: Home to trillions of bacteria known as the gut microbiota, the gut plays a key role in digestion, immune function, and communication with distant organs like the liver and eyes. Microbial metabolites such as short-chain fatty acids (SCFAs), including butyrate, and bile acids are important players in this system, influencing both the liver and brain
The Brain: The brain receives and processes signals from both the gut and liver, influencing mood, cognitive function, and visual processing. When the liver and gut are not functioning optimally, brain function, including vision, can be impaired.
The Liver: The liver processes nutrients from the gut, detoxifies harmful substances, and helps regulate blood flow to the eyes. It also produces bile acids, which are now recognized as signaling molecules that impact systemic inflammation and ocular health.
The inclusion of the eyes in this axis is an exciting development, particularly because of their vulnerability to immune dysregulation and metabolic changes. The health of one organ often affects the others, with disruptions in the gut or liver potentially leading to cognitive issues or even visual disturbances.
