What if the health of your gut were influencing far more than digestion? Emerging research suggests that the balance of microbes in the gut may affect inflammation throughout the body, with possible consequences for both brain health and vision. Scientists are uncovering connections that may reshape how we think about healthy aging.
Gut-Eye Axis
The gut and the eyes may seem unrelated, but they are connected through the immune system, inflammation, and nerve signaling. When the gut microbiota is in balance, it helps support healthy immune function and protective barriers throughout the body. When that balance is disrupted, a condition known as dysbiosis, inflammation can increase and may contribute to a range of eye problems. 1
Research suggests that gut dysbiosis may be associated with conditions such as uveitis, Behcet’s disease, Sjogren’s syndrome, and dry eye syndrome. In some cases, this may lead to reduced tear production or poorer tear quality, both of which can make the eyes feel dry, irritated, and uncomfortable. 2 Scientists have also found that lower levels of short-chain fatty acids, beneficial compounds produced by gut bacteria, may affect circadian rhythms and reduce secretion from the lacrimal glands, which help keep the eyes properly lubricated. 3
Gut-related inflammation may also affect deeper structures in the eye. Certain gut bacteria can contribute to the production of inflammatory compounds such as lipopolysaccharides, which may weaken the gut barrier and promote inflammation elsewhere in the body, including the retina. This may be relevant in conditions such as diabetic retinopathy.
Retinal Inflammation
Bacteroidetes in the gut produce lipopolysaccharides (LPS), which can damage the gut mucosal barrier and may contribute to retinal inflammation by increasing interleukin-6 (IL-6). 4 This may be particularly relevant to diabetic retinopathy.
Macular Degeneration (ARMD)
Gut dysbiosis has also been linked to age-related macular degeneration and may contribute to inappropriate complement activation, a possible mechanism in the gut-eye axis. 5
Glaucoma
An unhealthy balance of gut bacteria, called dysbiosis, may harm the blood-retinal barrier, which helps protect the eye. The gut microbiome plays an important role in building and maintaining this protective barrier.
Glaucoma is an eye disease that damages the optic nerve over time and can slowly reduce side vision. This happens when important eye cells, called retinal ganglion cells, begin to die.
Inflammation caused by gut imbalance may also affect microglia, which are cells that help protect the nervous system, including the eyes. When this protection is weakened, retinal ganglion cells may be more vulnerable to damage and degeneration.
Thyroid Eye Disease
Graves’ disease is an immune disorder in which autoantibodies stimulate the thyroid gland to overproduce thyroid hormone, resulting in hyperthyroidism. Dysbiosis can affect cytokines that are thought to drive inflammation and may also have a direct effect on thyroid hormone production.
Brain Inflammation, Gut Imbalances, Alzheimer’s Disease and Parkinson’s Disease
Alzheimer’s disease currently affects 1 in 10 adults over age 65 and 1 in 3 adults over age 85. Early signs often include memory loss, confusion, and trouble thinking clearly. Over time, the disease can gradually become severe enough to interfere with daily life and independence.
This is a multifaceted disease, meaning there are a number of ways normal brain function can be disrupted, including the brain’s housekeeping function of eliminating waste, maintenance of synapses, neurogenesis, mitochondrial function, and more.
Inflammation can be one of the key components affecting normal brain function.
Research suggests that chronic inflammation in the brain may play a role in the development of Alzheimer’s disease. 6
The gut microbiota consists of bacteria, fungi, archaea, viruses, and protozoa that live in the digestive system and normally work together to support health. When the balance of this complex community changes, a condition called dysbiosis can occur. Dysbiosis has been linked to aging and to the development of inflammatory disorders and disorders of the central nervous system, including Alzheimer’s disease. 7
In older adults, this imbalance in gut microbes may contribute to inflammation throughout the body. That inflammation may then worsen inflammation in the brain, which could further contribute to Alzheimer’s disease. Studies in mice have also shown that age-related changes in the gut microbiota can affect behavior and thinking, supporting the idea that changes in gut permeability and body-wide inflammation may play an important role. 8
External factors can affect gut microbiome balance, including obesity, 9 chronic stress, 10 a poor diet, 11 type 2 diabetes, 12 and excessive use of antibiotics. 13
Parkinson’s Disease
Recent research has found an important connection between the gut microbiota and Parkinson’s disease. A study led by the Nagoya University Graduate School of Medicine in Japan found that people with Parkinson’s disease had fewer gut bacteria carrying the genes needed to produce vitamin B2 (riboflavin) and vitamin B7 (biotin), two vitamins that are important for overall health. 14
The researchers also found that this shortage was linked to lower levels of substances that help maintain the intestinal barrier, the protective lining that keeps harmful toxins from leaking into the bloodstream. When this barrier becomes weakened, toxins may enter the body more easily and contribute to the inflammation seen in Parkinson’s disease.
Supplementing with these vitamins shows promise as a potential therapeutic approach for helping alleviate Parkinson’s disease symptoms and decreasing disease progression.
Previous studies indicated that changes in gut bacteria in Parkinson’s disease and the lack of B vitamins were linked to decreased levels of short-chain fatty acids and polyamines. These molecules in the gut help create a healthy mucus layer in the gut’s intestinal barrier. This thinning in the intestinal mucous lining and increased permeability have both been observed in Parkinson’s disease patients.
Such toxins may contribute to the overproduction of alpha-synuclein fibrils, which are molecules that accumulate in dopamine-producing cells in the substantia nigra, a region particularly relevant to patients with Parkinson’s disease. This can result in increased nervous system inflammation, resulting over time in more debilitating motor and dementia symptoms in Parkinson’s disease patients.
An older 2003 study found that high doses of riboflavin can assist in the recovery of some motor functions when combined with the elimination of red meat from the diet. 15
Nose-Gut Connection
Is it possible that in Parkinson’s disease patients, gut imbalance can begin with the nose-gut connection? Scientists are discovering a back-and-forth relationship between nasal, sinus, respiratory, and gut health. These systems are connected by shared immune pathways, inflammation, and microbiota. One theory is that gut dysbiosis may contribute to low-grade, system-wide inflammation that triggers chronic sinusitis, congestion, and allergies. Researchers are also asking whether the nose-gut connection and environmental exposures may contribute to Parkinson’s disease.
Possible contributors include:
- exposure to dry cleaning and degreasing chemicals
- use of herbicides and weed killers
- air pollution
- contaminated drinking water
Gut microbiome imbalance may contribute to the misfolding of alpha-synuclein proteins in the brain, which then accumulate in clumps known as Lewy bodies. Lewy bodies are found in Parkinson’s disease and Alzheimer’s disease patients. 16
Lifestyle Considerations
While research on the gut-brain connection is still evolving, the encouraging news is that everyday habits may help support both gut health and brain health as we age. Diet, exercise, sleep, stress management, and social connection all influence inflammation, metabolism, and the balance of microbes in the gut. 17 Together, these factors may play a meaningful role in protecting memory, mood, and long-term cognitive function.
One of the most practical places to start is with food. A diet rich in vegetables, fruits, legumes, whole grains, nuts, seeds, and healthy fats can help nourish beneficial gut bacteria. Fermented foods such as yogurt, kefir, sauerkraut, and kimchi may also help support a healthier gut microbiota. At the same time, reducing highly processed foods, excess sugar, and unhealthy fats may help lower inflammation that can affect both the gut and the brain.
Regular physical activity is another powerful tool. Exercise has been associated with better learning and memory, lower inflammation, healthier brain cell function, 18 and reduced loss of nerve cells over time. 19 Even moderate activity, such as walking, strength training, stretching, or balance exercises, can be beneficial when done consistently. In addition, getting enough sleep, staying mentally engaged, managing stress, and maintaining strong social ties may all support healthier aging. 20
Although no single habit can prevent neurodegenerative disease, these lifestyle choices offer real, practical ways to support overall well-being. Small, steady changes can make a meaningful difference over time, helping people take an active role in caring for both the gut and the brain.
Suggested Supplements
Dr. Grossman’s Complete Eye Formula 2oz (oral spray)
Advanced Eye & Vision Support Formula (whole food) 60 vcaps
Dr. Grossman’s Meso Plus Retinal Support and Computer Eye Strain Formula with Astaxanthin 90 vcaps
Dr. Grossman’s Advanced Eye and Dr. G’s Whole Food Superfood Multi1 20 Vcap Combo – 2 months supply
ReVision Formula (wild-crafted herbal formula) 2 oz – based on classic Chinese medicine Liver tonic formula to help support healthy circulation and blood flow throughout the eyes and body.
Cognirev Extra Strength 2 oz Oral Spray
Brain and Memory Power Boost 120 caps
Dr. Grossman’s Vitamin C Plant-Based Formula – 60 caps
Dr. Grossman’s Premium Turmeric Vcaps (Organic)
Brain and Memory Support Package 1
Recommended Books
Natural Eye Care: Your Guide to Healthy Vision and Healing
Natural Parkinson’s Support: Your Guide to Preventing and Managing Parkinson’s
- Taylor R. The Gut and the Eye. EyeNet Magazine. 2020 Oct 1. Available from: https://www.aao.org/eyenet/article/the-gut-and-the-eye#disqus_thread ↩
- Moon J, Choi SH, Yoon CH, Kim MK, Appel S. Gut dysbiosis is prevailing in Sjogren’s syndrome and is related to dry eye severity. PLoS One. 2020;15(2):e0229029. doi:10.1371/journal.pone.0229029 ↩
- Jiao X, Pei X, Dingli L, et al. Microbial reconstitution improves aging-driven lacrimal gland circadian dysfunction. Am J Pathol. 2021;191(12):2091-2116. doi:10.1016/j.ajpath.2021.08.006 ↩
- Tanase DM, Gosav EM, Neculae E, et al. Role of gut microbiota on onset and progression of microvascular complications of type 2 diabetes (T2DM). Nutrients. 2020;12(12):3719. doi:10.3390/nu12123719 ↩
- Zinkernagel MS, Zysset-Burri DC, Keller I, et al. Association of the intestinal microbiome with the development of neovascular age-related macular degeneration. Sci Rep. 2017;7(1). doi:10.1038/srep40826 ↩
- Calsolaro V, Edison P. Neuroinflammation in Alzheimer’s disease: current evidence and future directions. Alzheimers Dement. 2016;12(6):719-732. doi:10.1016/j.jalz.2016.02.010 ↩
- Friedland RP, Chapman MR. The role of microbial amyloid in neurodegeneration. PLoS Pathog. 2017;13(12):e1006654. doi:10.1371/journal.ppat.1006654 ↩
- Scott KA, Ida M, Peterson VL, Prenderville JA, Moloney GM, Izumo T, et al. Revisiting Metchnikoff: age-related alterations in microbiota-gut-brain axis in the mouse. Brain Behav Immun. 2017;65:20-32. doi:10.1016/j.bbi.2017.02.004 ↩
- Naseer MI, Bibi F, Alqahtani MH, Chaudhary AG, Azhar EI, Kamal MA, et al. Role of gut microbiota in obesity, type 2 diabetes and Alzheimer’s disease. CNS Neurol Disord Drug Targets. 2014;13(2):305-311. doi:10.2174/18715273113126660147 ↩
- Bangasser DA, Dong H, Carroll J, Plona Z, Ding H, Rodriguez L, et al. Corticotropin-releasing factor overexpression gives rise to sex differences in Alzheimer’s disease-related signaling. Mol Psychiatry. 2017;22(8):1126-1133. doi:10.1038/mp.2016.185 ↩
- Claesson MJ, Jeffery IB, Conde S, Power SE, O’Connor EM, Cusack S, et al. Gut microbiota composition correlates with diet and health in the elderly. Nature. 2012;488(7410):178-184. doi:10.1038/nature11319 ↩
- Beli E, Yan Y, Moldovan L, Vieira CP, Gao R, Duan Y, et al. Restructuring of the gut microbiome by intermittent fasting prevents retinopathy and prolongs survival in db/db mice. Diabetes. 2018;67(9):1867-1879. doi:10.2337/db18-0158 ↩
- Wang T, Hu X, Liang S, Li W, Wu X, Wang L, et al. Lactobacillus fermentum NS9 restores the antibiotic induced physiological and psychological abnormalities in rats. Benef Microbes. 2015;6(5):707-717. doi:10.3920/BM2014.0177 ↩
- Minato T, Maeda T, Fujisawa Y, Tsuji H, Nomoto K, Ohno K, et al. Progression of Parkinson’s disease is associated with gut dysbiosis: two metagenome-wide association studies. BMC Genomics. 2024;25:435. Available from: https://en.nagoya-u.ac.jp/news/articles/research_information_215/ ↩
- Coimbra CG, Junqueira VB. High doses of riboflavin and the elimination of dietary red meat promote the recovery of some motor functions in Parkinson’s disease patients. Braz J Med Biol Res. 2003;36(10):1409-1417. doi:10.1590/S0100-879X2003001000019. PMID:14502375 ↩
- Klingelhoefer L, Reichmann H. Pathogenesis of Parkinson disease-the gut-brain axis and environmental factors. Nat Rev Neurol. 2015;11(11):625-636. PMID:38773112 ↩
- Bruce-Keller AJ, Salbaum JM, Luo M, et al. Obese-type gut microbiota induce neurobehavioral changes in the absence of obesity. Biol Psychiatry. 2015;77(7):607-615. doi:10.1016/j.biopsych.2014.07.012 ↩
- Lu Y, Dong Y, Tucker D, Wang R, Ahmed ME, Brann D, et al. Treadmill exercise exerts neuroprotection and regulates microglial polarization and oxidative stress in a streptozotocin-induced rat model of sporadic Alzheimer’s disease. J Alzheimers Dis. 2017;56(4):1469-1484. doi:10.3233/JAD-160869 ↩
- Papenberg G, Ferencz B, Mangialasche F, Mecocci P, Cecchetti R, Kalpouzos G, et al. Physical activity and inflammation: effects on gray-matter volume and cognitive decline in aging. Hum Brain Mapp. 2016;37(10):3462-3473. doi:10.1002/hbm.23252 ↩
- Papenberg G, Ferencz B, Mangialasche F, Mecocci P, Cecchetti R, Kalpouzos G, et al. Physical activity and inflammation: effects on gray-matter volume and cognitive decline in aging. Hum Brain Mapp. 2016;37(10):3462-3473. doi:10.1002/hbm.23252 ↩
