Most of my health-conscious readers already know about "leaky gut" — a weakened intestinal lining that lets things into the bloodstream that shouldn't be there. Fewer people know that the brain has its own version of this problem. It's called blood-brain barrier breakdown, and new research shows it may be one of the earliest signs of memory and thinking problems — showing up before the changes doctors usually test for.
The blood-brain barrier is a tightly sealed wall of cells lining the blood vessels of the brain. It keeps toxins, germs, and inflammatory substances out of brain tissue, while letting oxygen and nutrients in. Think of it as security screening for everything trying to reach your brain.
When this barrier breaks down, it starts to leak. Unwanted substances slip through into brain tissue, where they can interfere with the way brain cells communicate and function. Damage to small blood vessels in the brain is now thought to play a role in roughly half of all dementia cases worldwide, including many cases of Alzheimer's disease.
For years, most Alzheimer's research focused on two proteins: amyloid-beta and tau. Blood vessel damage was treated as a side effect of these proteins, not a cause of its own. A landmark 2019 study by Daniel Nation and colleagues, published in Nature Medicine, put that assumption to the test.
The researchers studied 161 older adults at two research centers. Some had normal memory and thinking. Others showed early signs of decline. The team measured two things: a biomarker in spinal fluid called sPDGFRβ, which is released when the cells supporting brain capillaries are damaged, and direct measurements of blood-brain barrier leakiness using a specialized brain MRI scan.
The results were clear. The biomarker of vessel damage rose step by step as memory and thinking problems worsened. MRI scans confirmed real leaking of the barrier specifically in the hippocampus — the brain's memory center — and in the nearby parahippocampal gyrus. Both changes showed up in people with early cognitive decline whether or not their amyloid-beta or tau levels were abnormal.
This is the part that changes the conversation. Barrier breakdown in the hippocampus predicted thinking and memory problems even after the researchers accounted for amyloid-beta, tau, brain shrinkage, age, and standard vascular risk factors like high blood pressure, diabetes, and heart disease. It also had nothing to do with general inflammation or nerve cell injury markers.
In plain terms: a leaky blood-brain barrier in the memory center of the brain appears to be its own distinct problem — not just a downstream result of the amyloid or tau buildup that usually gets the spotlight.
The cells most responsible for keeping the barrier sealed are called pericytes. They wrap around the tiny blood vessels (capillaries) in the brain and help control what passes through the vessel wall. When pericytes are stressed or injured, they release the sPDGFRβ biomarker measured in this study — essentially a distress signal that shows up in spinal fluid.
Laboratory experiments confirmed that pericytes release far more of this biomarker than other vascular cells, and that an enzyme called ADAM10 drives the release when cells are under stress. Damaged pericytes mean a weaker, leakier barrier — and a brain more exposed to substances it's supposed to be shielded from.
The leak in this study was not spread evenly across the brain. It showed up specifically in the hippocampus and its sub-regions, along with the parahippocampal gyrus — not in the frontal cortex, temporal cortex, white matter, thalamus, or other regions tested. This lines up closely with the memory complaints that typically mark the earliest stage of cognitive decline, since the hippocampus is the brain structure most responsible for forming new memories.
Since the original 2019 study, follow-up research has continued to build the case for a leaky blood-brain barrier as a meaningful player in brain aging.
A 2024 longitudinal study followed 334 people at a memory clinic and found that greater blood-brain barrier permeability was linked to a higher likelihood of cognitive decline progressing over time — more than half of participants with higher barrier leakiness went on to decline further.
A 2025 study of 83 older adults without dementia, followed for up to five years, found that higher levels of the same sPDGFRβ biomarker were tied to a faster rate of decline in memory, language, attention, and executive function over time — especially in people who already carried Alzheimer's-related biomarkers or the APOE ε4 gene variant, a well-known genetic risk factor for Alzheimer's.
A comprehensive 2025 scientific review brought together the growing body of evidence on blood-brain barrier and blood vessel biomarkers, confirming that barrier breakdown is now recognized as an early step in the development of Alzheimer's disease and related dementias, and highlighting new blood-based tests being developed to detect it.
There is a lot you can do to create a healthy blood brain barrier through the foods you consume and even supplementation. There is a lot of overlap with the recommended foods and supplements used for leaky gut. I have many articles and videos on this at markstengler.com and in my book The Holistic Guide to Gut Health.
A comprehensive 2025 scientific review examined the plant compounds with the strongest evidence for protecting the cells that make up the blood-brain barrier. Flavonoids, anthocyanins, carotenoids, and related polyphenols — the pigments concentrated in berries, leafy greens, colorful vegetables, and olive oil — act directly on brain endothelial cells. They reinforce the tight junction proteins that seal the barrier shut, calm inflammatory signaling within brain blood vessels, and reduce the oxidative stress that damages the vessel lining over time. The review also highlighted vitamin D, sulforaphane from cruciferous vegetables like broccoli and Brussels sprouts, and the polyphenol metabolite urolithin — produced in the gut from foods like pomegranates and walnuts — as compounds with anti-inflammatory and barrier-reinforcing effects backed by a growing body of research. Together, this evidence points to a dietary pattern built around fatty fish, colorful produce, olive oil, and cruciferous vegetables as one of the most direct, food-based ways to support a well-sealed blood-brain barrier.
Omega-3 fatty acids have the strongest direct human evidence for supporting blood-brain barrier integrity. A 2021 study of 45 healthy older adults measured blood-brain barrier permeability directly with the same DCE-MRI technique used in the hippocampus research above. People with higher blood levels of the long-chain omega-3s DHA and EPA — the types found in fatty fish like salmon, sardines, and mackerel — showed significantly less barrier leakiness in the internal capsule, a deep brain region vulnerable to age-related decline. Higher omega-3 levels also trended toward better memory and language performance in the same participants. This is the first study to confirm in living humans what animal research had already shown: diets rich in long-chain omega-3s are tied to a tighter, better-sealed blood-brain barrier.
This growing body of research reframes what protecting your memory and thinking as you age actually requires. It is not only about managing amyloid and tau. It is also about protecting the blood vessels that supply the brain and the pericyte cells that keep those vessels sealed. A leaky blood-brain barrier, much like a leaky gut, allows material into a space that depends on being tightly controlled.
Blood-brain barrier breakdown is now established as a measurable, early, and independent warning sign of cognitive decline — not simply a footnote to the amyloid and tau story. For anyone focused on long-term brain health, vascular integrity deserves a central place in the conversation.
Barnes, S., Chowdhury, S., Gatto, N. M., Fraser, G. E., & Lee, G. J. (2021). Omega-3 fatty acids are associated with blood-brain barrier integrity in a healthy aging population. Brain and Behavior, 11(8), e2273. https://doi.org/10.1002/brb3.2273
Edwards, L., Gonzalez, A. I., Thomas, K. R., Smirnov, D. S., Brenner, E. K., Nation, D. A., Chang, F., Blennow, K., Salmon, D. P., Galasko, D., & Bangen, K. J. (2025). Interactive effects of blood-brain barrier breakdown and Alzheimer's disease biomarker status on cognitive decline in older adults without dementia. Alzheimer's & Dementia, 21(11), e70910. https://doi.org/10.1002/alz.70910
French, S. R., Meyer, B. P., Arias, J. C., Levendovszky, S. R., & Weinkauf, C. C. (2025). Biomarkers of blood–brain barrier and neurovascular unit integrity in human cognitive impairment and dementia. Alzheimer's & Dementia, 21(3), e70104. https://doi.org/10.1002/alz.70104
Kocsis, A. E., Kucsápszky, N., Santa-Maria, A. R., Hunyadi, A., Deli, M. A., & Walter, F. R. (2025). Much more than nutrients: The protective effects of nutraceuticals on the blood-brain barrier in diseases. Nutrients, 17(5), 766. https://doi.org/10.3390/nu17050766
Nation, D. A., Sweeney, M. D., Montagne, A., Sagare, A. P., D'Orazio, L. M., Pachicano, M., Sepehrband, F., Nelson, A. R., Buennagel, D. P., Harrington, M. G., Benzinger, T. L. S., Fagan, A. M., Ringman, J. M., Schneider, L. S., Morris, J. C., Chui, H. C., Law, M., Toga, A. W., & Zlokovic, B. V. (2019). Blood-brain barrier breakdown is an early biomarker of human cognitive dysfunction. Nature Medicine, 25(2), 270–276. https://doi.org/10.1038/s41591-018-0297-y
Puig-Pijoan, A., Jimenez-Balado, J., Fernández-Lebrero, A., et al. (2024). Risk of cognitive decline progression is associated to increased blood-brain-barrier permeability: A longitudinal study in a memory unit clinical cohort. Alzheimer's & Dementia, 20(1), 538–548. https://doi.org/10.1002/alz.13433
