Constipation and dementia are linked. In 462,327 middle-aged and older adults, constipation came before dementia with 50% added risk. In real numbers, 7.0% of people with constipation went on to stroke, dementia or Parkinson’s disease, against 4.3% without it. Real, and modest.
A sixty-eight-year-old woman came to me about words. Nouns, mostly, and the names of people she had known for decades. Her screening score was called borderline, and she was told to come back in a year. Nobody asked about the constipation she had handled with two laxatives since her early fifties.
That order, bowel first and memory second, is why constipation and dementia belong in the same talk. I am Dr. Gurpreet Singh Padda, MD, MBA, MHP. The video above covers the brain-barrier scans and the bacteria debate from The Angry Gut, the book I wrote with Ami Michelle Grimes. This page goes further. It covers real-number risk, the hidden factors inside stool research, and what a pain practice does with a patient like her.
The gut is the first brain. The skull holds the second. The vagus nerve ties them together, and they share a blood supply. When one of them has been inflamed for sixteen years, the other is not a bystander.
A clean colonoscopy is not a clean bill of health
Her colonoscopy in her late fifties found nothing. A scope answers one narrow question: is cancer growing on the colon wall? It cannot tell you how fast the tube moves or what crosses its lining. A normal scope became a closed file.
The reason is the billing map. Her bowel belongs to one specialist and her memory to another. No billing code pays either one to ask about the other organ. The patient is left carrying the link alone. People in chronic pain know this setup well. A spine doctor, a psychiatrist and a gut doctor never compare notes. That is exactly why a scan that does not match the pain so often ends a workup instead of starting one.
Is constipation linked to dementia? What large cohorts show
The biggest dataset followed 462,327 middle-aged and older adults. Constipation came before a combined outcome of stroke, dementia and Parkinson’s disease, at an adjusted hazard ratio of 1.35. Broken out, the added risk was 20% for stroke, 50% for dementia and 56% for Parkinson’s (Yun et al., 2025).
Now the real numbers. Among people with constipation, 1,415 of 20,263 went on to one of those events, or 7.0%. Among people without it, 18,848 of 442,064 did, or 4.3%. That is a 2.7-point gap over years of follow-up. Real, and modest. How the constipation was recorded changed the answer too. Self-report carried a hazard ratio of 1.31. A coded diagnosis carried 1.44.
Stroke on that list is the tell. A bowel signal that predicts three different brain diseases is not pointing at one plaque or one misfolded protein. It is pointing at shared terrain, loaded with metabolic and inflammatory stress, that can fail in more than one direction. The link was also strongest in the first two years. That is the pattern you see when the brain disease itself causes the constipation. Both readings can be true at once.
Parkinson’s disease gives the sharpest version. A national database compared it with healthy people and with Alzheimer’s and stroke-related disease. Four gut problems came first specifically in Parkinson’s: a stomach that empties too slowly, trouble swallowing, irritable bowel without diarrhea, and constipation (Konings et al., 2023). Diarrhea and fecal incontinence did not set it apart. The slow bowel carried the signal, not the loose one.
Can you trust a microbiome stool test if you are constipated?
Here is what most microbiome marketing leaves out. Stool texture moves every headline number a microbiome kit reports. That includes richness, the balance between the major bacteria groups, and the enterotype label (Vandeputte et al., 2016). In 53 healthy women, faster transit favored fast-growing species. Bacteria that survive a fast tube divide quickly. Slow the tube and a different crowd wins.
People with Parkinson’s are constipated at an odds ratio of 6.1 against controls in the largest gene-based gut study. They used laxatives at an odds ratio of 3.8 (Wallen et al., 2022). That team ran the test that settles the question in people who did not have the disease. Constipation caused the same drop in spore-forming gene groups in healthy people — an even stronger one. It was a fold change of 0.58 in healthy people against 0.76 in the Parkinson’s group.
So a species list from a constipated person is mostly a readout of the constipation. The census is not the activity. It counts who lives in the tube, not what they did today. A bowel habit can be treated. It deserves a plan before anyone sells you a species list as a diagnosis.
How does gut inflammation reach the brain?
What actually travels from the first brain to the second? On the best-controlled evidence, it is traffic, not a colony. Bacterial products and immune signals cross a barrier that no longer closes well.
Twelve healthy young men got endotoxin (a bacterial toxin) through an IV. They developed fever and a surge in interleukin-6, cortisol and norepinephrine. Yet memory, attention and planning did not budge (Grigoleit et al., 2010). But a single dose in healthy volunteers is not sixteen years of an inflamed bowel in a woman in her late sixties. Trial entry rules screen that patient out.
The long-term picture looks different. Among 217 older adults, about a third had thinking problems. That group had interleukin-6 three times higher. Their stool calprotectin was four times higher. Calprotectin is the protein white cells leave behind in an inflamed bowel. The strongest single link with thinking was stool calprotectin, at r = -0.573 (Arikawa et al., 2025). The study is a one-time snapshot and was not adjusted for age. But it points at the bowel, not the blood.
For someone living with chronic pain, this lands twice. The metabolic inflammation that loosens a barrier is the same engine that keeps a nervous system on high alert. That is why high insulin can make you hurt. It is also why belly fat pumps out inflammatory signals long before a memory score slips. The spinal side of that traffic is the subject of how the gut reaches the spine.
The gums, and a pill that did not hold
The mouth is the likeliest open door. Check the gums after a dementia diagnosis, and the pooled odds ratio is 2.26. Measure the gums first and follow people forward, and the hazard ratio shrinks to 1.15 (Kim & Han, 2025). The gap between those two figures comes from faulty memory of the past. And severe disease carried the whole link.
Then a drug was built to block the gum bacterium’s protein-cutting enzymes. It was tested in 643 people with mild to moderate Alzheimer’s disease. Every group declined by about the same amount. It missed both main goals. Liver enzymes rose past three times normal in 7 and 15 percent on the two doses. And the program was stopped (Alzforum, 2022). People also left the drug groups faster: 163 of 217 finished on placebo, against 129 of 214 on the high dose (Cortexyme, 2022).
A late pill in established disease is not the same as closing a door early. Severe gum disease is still an inflammatory load you can treat.
What a pain practice does with a slow gut and a slipping memory
Here is what I told her.
- The barrier problem is metabolic before it is neurological. In healthy older adults, a high body mass index and waist-hip ratio predicted a leaking brain barrier twenty years later. That leak tracked diabetes, not amyloid or APOE genes (Janelidze et al., 2017). So the levers are the ones that move a waistline and a fasting insulin: what you eat, when you eat, how you sleep and whether you move.
- Ask why the bowel stopped. A laxative keeps things moving. It never asks the question. Stool calprotectin is a simple way to start asking.
- Get the gums examined with numbers. If there is severe gum disease, treat it as the inflammatory load it is.
- Write down the years your bowel changed and your memory did.
None of this means stopping a laxative or any other medicine on your own. Work every change through with your doctor. Chronic pain adds its own layer to the memory question. Whether chronic pain raises dementia risk deserves the same visit. Every study behind these figures, with its limits, is in the Deep Dive for Chapter 12. The next step down the same system is what unresolved trauma does to the bowel.
Seal the first brain anyway. The metabolic case for it does not wait on the bacteria debate.
Frequently asked questions
Can constipation cause dementia?
A link is not proof of cause. In a group of 462,327 adults, people with constipation had 50% higher dementia risk. The link was strongest in the first two years. That also fits a slow brain disease that shows up in the gut first. See how the vagus nerve carries signals between the gut and the brain.
Is gum disease linked to dementia?
Yes, but less strongly than headlines suggest. Studies that check gums after diagnosis show about double the odds. Studies that follow people forward find a hazard ratio of 1.15. And only severe disease carries the link. Severe gum disease is still inflammation worth treating. Read why we treat inflammatory load at its metabolic source.
Can gut inflammation cause brain fog?
Long-term gut inflammation travels with thinking problems in older adults. In 217 people, those with thinking problems had stool calprotectin four times higher and interleukin-6 three times higher. Stool calprotectin tracked thinking more strongly than any blood marker. The study was a one-time snapshot, so it shows a link, not a cause. Learn how a fire in the gut shows up as anxiety and mood symptoms.
Should I get a microbiome stool test for memory problems?
Be careful. Stool texture drives most of what a microbiome kit reports. Constipation alone causes the same bacteria pattern seen in Parkinson’s disease, even in healthy people. A species list from a slow bowel is mostly a report on the slow bowel. Stool calprotectin, which measures inflammation, is often the more useful question. Find out why the popular leaky gut test cannot see the gut wall.
What should I bring to a memory appointment if I have gut symptoms?
Bring a timeline with years, not decades. When did bowel symptoms start? When did memory change? Which laxatives or other medicines do you use? Ask about your waist size and fasting insulin in the same visit, since body size and diabetes tracked a leaking brain barrier. Ask whether stool calprotectin makes sense for you. See what a computerized cognitive assessment measures.
Is constipation an early sign of Parkinson’s disease?
It can come first. A national database compared Parkinson’s disease with healthy people and with other brain diseases. Four gut problems came before it specifically, constipation among them. In the largest group, constipation carried 56% added risk for Parkinson’s. Diarrhea and fecal incontinence did not set it apart. The slow bowel carried the signal, not the loose one.
Does a normal colonoscopy mean my bowel is healthy?
No. A colonoscopy answers one narrow question: is cancer growing on the colon wall? It cannot tell you how fast the bowel moves or what crosses its lining. A normal scope too often becomes a closed file. But a slow bowel still deserves a plan and a question about why it stopped. Stool calprotectin is a simple way to start asking.
Memory changes and a gut nobody asked about?
We look at the whole terrain — the bowel, the metabolic numbers and the nervous system — in one plan, not three waiting rooms. Bring your timeline and we will start there.
Request an appointment, or call or text us.
Sources
- Yun, Q., Wang, S., Li, B., Yang, Z., Wei, C., Yuan, J., Hu, J., Li, Y., Yang, Z., Sha, F., & Tang, J. (2025). Constipation preceding stroke, dementia and Parkinson’s disease in middle-aged and older adults: a population-based cohort study. Age and Ageing, 54(9), afaf257. https://doi.org/10.1093/ageing/afaf257
- Konings, B., Villatoro, L., Van den Eynde, J., Barahona, G., Burns, R., McKnight, M., Hui, K., Yenokyan, G., Tack, J., & Pasricha, P. J. (2023). Gastrointestinal syndromes preceding a diagnosis of Parkinson’s disease: testing Braak’s hypothesis using a nationwide database for comparison with Alzheimer’s disease and cerebrovascular diseases. Gut, 72(11), 2103-2111. https://doi.org/10.1136/gutjnl-2023-329685
- Wallen, Z. D., Demirkan, A., Twa, G., Cohen, G., Dean, M. N., Standaert, D. G., Sampson, T. R., & Payami, H. (2022). Metagenomics of Parkinson’s disease implicates the gut microbiome in multiple disease mechanisms. Nature Communications, 13(1), 6958. https://doi.org/10.1038/s41467-022-34667-x
- Vandeputte, D., Falony, G., Vieira-Silva, S., Tito, R. Y., Joossens, M., & Raes, J. (2016). Stool consistency is strongly associated with gut microbiota richness and composition, enterotypes and bacterial growth rates. Gut, 65(1), 57-62. https://doi.org/10.1136/gutjnl-2015-309618
- Arikawa, A. Y., Waterman, A., Mishra, S. P., Labyak, C., Williams, C., Chaudhari, D. S., Shukla, R., Kumar, V., Masternak, M., Holland, P., Golden, A., Dangiolo, M., Kociolek, J., Fraser, A., Agronin, M., Aymat, M., Yadav, H., & Jain, S. (2025). Cognitive impairment is associated with alterations in diet quality and inflammatory biomarkers in older adults: a cross-sectional analysis of data collected from the Microbiome in Aging Gut and Brain (MiaGB) Consortium cohort. The Journal of Nutrition, Advance online publication (PubMed record carries no volume/issue/pages). https://doi.org/10.1016/j.tjnut.2025.06.026
- Grigoleit, J. S., Oberbeck, J. R., Lichte, P., Kobbe, P., Wolf, O. T., Montag, T., del Rey, A., Gizewski, E. R., Engler, H., & Schedlowski, M. (2010). Lipopolysaccharide-induced experimental immune activation does not impair memory functions in humans. Neurobiology of Learning and Memory, 94(4), 561-7. https://doi.org/10.1016/j.nlm.2010.09.011
- Kim, D.-H., & Han, G.-S. (2025). Periodontitis as a risk factor for dementia: A systematic review and meta-analysis. The Journal of Evidence-Based Dental Practice, 25(2), 102094. https://doi.org/10.1016/j.jebdp.2025.102094
- Cortexyme, Inc. (sponsor). ClinicalTrials.gov registry record NCT03823404. (2022). GAIN Trial: A randomized, double-blind, placebo-controlled study of COR388 in subjects with Alzheimer’s disease. https://clinicaltrials.gov/study/NCT03823404
- Alzforum (Biomedical Research Forum, LLC). Therapeutics database entry: Atuzaginstat. (2022). Atuzaginstat (COR388) – Alzforum Therapeutics entry. https://www.alzforum.org/therapeutics/atuzaginstat
- Janelidze, S., Hertze, J., Nägga, K., Nilsson, K., Nilsson, C., Wennström, M., van Westen, D., Blennow, K., Zetterberg, H., & Hansson, O. (2017). Increased blood-brain barrier permeability is associated with dementia and diabetes but not amyloid pathology or APOE genotype. Neurobiology of Aging, 51, 104-112. https://doi.org/10.1016/j.neurobiolaging.2016.11.017
Dr. Gurpreet Singh Padda, MD, MBA, MHP
