Can Bacterial Infections Increase the Risk of Dementia?

Written By Dr. Jessica Knape

Medically Reviewed by Dr Jessica Knape, MD MA. Board Certified in Internal Medicine and Integrative and Holistic Medicine

Short answer

Yes—certain bacterial infections are linked to a higher risk of cognitive decline. Some act indirectly by driving long-term inflammation (for example, chronic gum disease), while others can directly affect the brain or trigger episodes of delirium that accelerate decline in vulnerable adults. Understanding these links helps us prevent problems early, work up reversible causes, and protect long-term brain health.

At HealthSpan Internal Medicine in Boulder, CO, we emphasize evidence-based evaluation of infectious and inflammatory contributors to cognitive change, then build a personalized plan to treat root causes and restore brain resilience.

Overview

  • Chronic bacterial burdens (periodontal disease, chronic H. pylori, recurrent UTIs) are associated with higher dementia risk via systemic inflammation and immune activation.

  • Some infections can involve the nervous system directly (neurosyphilis, neuroborreliosis/Lyme).

  • Work-up includes history, oral/dental assessment, targeted infection tests, inflammatory markers, cognition screening, and (when indicated) brain imaging.

  • Treatment focuses on eradicating confirmed infections, reducing inflammation, rehabilitating the brain, and strengthening future defenses (oral care, vaccines, metabolic health).

How Bacteria Can Affect the Brain

  1. Chronic inflammation (“inflammaging”)
     Long-standing infections keep the immune system switched on. Circulating inflammatory molecules cross-talk with the brain’s immune cells (microglia), promoting neuroinflammation that can impair memory and processing speed.

  2. Endotoxins and barrier effects
     Bacterial components such as LPS (lipopolysaccharide) can disrupt the gut and blood-brain barriers, allowing more inflammatory signals to reach brain tissue.

  3. Direct nervous system involvement
     Certain bacteria can infect the nervous system (e.g., Treponema pallidum causing neurosyphilis; Borrelia burgdorferi in Lyme neuroborreliosis), leading to cognitive and psychiatric symptoms if untreated.

  4. Acute illness → delirium → decline
     In older adults, infections like UTIs or pneumonia often trigger delirium (sudden confusion). Even after the infection clears, some patients experience a step-down in baseline cognition.

Common Bacterial Links to Cognitive Decline

  • Periodontal (gum) disease: Chronic infection with organisms such as Porphyromonas gingivalis is associated with higher dementia risk. Mechanisms include bloodstream spread of bacterial products, systemic inflammation, and potential effects on amyloid pathways. Good oral care and periodontal treatment are protective.

  • Helicobacter pylori (H. pylori): This stomach bacterium is linked to systemic inflammation, B12/iron deficiency, and higher dementia risk in some studies. Eradication can improve nutrition, reduce inflammation, and may benefit cognition indirectly.

  • Recurrent UTIs: Especially in older adults, UTIs commonly provoke delirium and hospitalization. Repeated inflammatory hits and periods of inactivity can accelerate cognitive decline.

  • Lyme disease (Borrelia): Neurologic involvement (neuroborreliosis) can cause cognitive changes. Proper testing and guideline-based treatment are essential.

  • Atypical/respiratory bacteria: Severe pneumonia and sepsis are linked with later cognitive impairment, likely through inflammatory and vascular pathways.

  • Neurosyphilis: A rare but important “can’t-miss” cause of reversible dementia syndrome; treatable when identified.

Note: Association doesn’t always mean causation. The strongest clinical wins come from identifying and treating clear, active infections and removing ongoing inflammatory drivers (like poor oral health or recurrent UTIs).

Red Flags Suggesting an Infectious Contributor

  • Subacute cognitive decline following an acute infection (UTI, pneumonia, Lyme, etc.)

  • Cognitive symptoms with headaches, gait change, or neurologic findings

  • History of advanced periodontal disease, chronic reflux/ulcer symptoms, or long-standing dyspepsia (possible H. pylori)

  • Recurrent fevers, night sweats, or unexplained weight loss

  • Episodes of delirium or sudden confusion during infections

Recommended Work-Up (What We Check and Why)

  1. History & Exam

  • Timeline of cognitive changes; link to illnesses, dental procedures, travel, tick exposure, or antibiotics

  • Oral/dental assessment (ask about bleeding gums, tooth loss, periodontitis)

  • Review of sleep, mood, medications (anticholinergics), alcohol use, and metabolic health

    2. Baseline Labs (safety and contributors)

  • CBC, CMP, fasting glucose/A1c, lipids

  • B12, folate, vitamin D, ferritin/iron studies (deficiencies can mimic or worsen cognitive symptoms)

  • High-sensitivity CRP ± ESR (inflammation context)

  • Thyroid panel (thyroid dysfunction affects cognition)


    3. Targeted Infection Testing (case-by-case)

  • Periodontal disease: Dental/periodontal evaluation; consider referral for deep cleaning and periodontal therapy

  • H. pylori: Stool antigen or urea breath test (noninvasive, preferred)

  • UTIs: Urinalysis and urine culture (avoid overtreatment of asymptomatic bacteriuria unless criteria met)

  • Lyme disease: Two-tier testing (ELISA/EIA followed by Western blot/confirmatory immunoassay) when exposure risk and symptoms fit

  • Syphilis: RPR (or VDRL) with confirmatory treponemal test when appropriate

  • Other tests are individualized (e.g., blood cultures in sepsis, TB screening based on risk)

    4. Cognitive & Imaging

  • Brief cognitive screening (MoCA or similar) to set a baseline and track progress

  • Brain MRI if atypical features, stepwise decline, focal deficits, or to rule out structural causes

Treatment: What Actually Helps

  1. Eradicate Confirmed Infections

  • Periodontal therapy: Professional scaling/root planing; consistent home oral care; treat peri-implant disease if present

  • H. pylori: Guideline-based combination therapy and confirmation of eradication

  • UTIs: Treat true infections per culture; address contributors (hydration, bladder habits, vaginal estrogen therapy for postmenopausal women, urology referral for recurrent cases)

  • Lyme disease: Treatment per ILADS guidelines

  • Neurosyphilis: ID referral and IV penicillin per guidelines


    2. Reduce Systemic Inflammation

  • Mediterranean-style eating pattern (fiber, polyphenols, omega-3s)

  • Optimize oral hygiene: soft toothbrush, interdental cleaning, antimicrobial rinses as directed

  • Manage sleep apnea, blood pressure, glucose, and lipids (vascular health supports brain health)


    3. Support Brain & Mitochondria

  • Physical activity with resistance training (improves inflammation, insulin sensitivity, and neurotrophic factors)

  • Key nutrients as indicated: omega-3s, B-complex (with methylated B12/folate if deficient), vitamin D, magnesium

  • Address mood, sleep, and social engagement (all improve cognitive outcomes)


    4. Rehabilitation & Follow-Up

  • Cognitive exercises, hearing/vision optimization, and fall-prevention strategies

  • Recheck cognition (e.g., MoCA) after treatment and lifestyle changes

  • Dental follow-up to maintain periodontal health; UTI prevention plan for those at risk

What Not to Do

  • Don’t start antibiotics “just in case” without evidence of infection—this can cause harm and resistance.

  • Don’t ignore oral health—periodontal disease is a modifiable risk factor.

  • Don’t treat asymptomatic bacteriuria in older adults unless specific criteria are met (your clinician will guide you).

  • Don’t assume all cognitive decline is “just aging”—screen for reversible factors early.

When to Seek Care Urgently

  • Sudden confusion, fever, or severe headache

  • New neurologic deficits (weakness, trouble speaking, facial droop)

  • Altered mental status with suspected infection (possible sepsis or meningitis)

How We Help at HealthSpan Internal Medicine

Our approach combines conventional and functional medicine to address both cause and consequence:

  1. Comprehensive history, physical and lifestyle assessment

  2. Targeted infectious and inflammatory testing

  3. Guideline-based eradication of confirmed infections

  4. Anti-inflammatory nutrition, oral-care plan, and metabolic optimization

  5. Brain rehabilitation, exercise prescription, and follow-up cognition tracking

Our goal is simple: identify what’s driving inflammation, treat what’s treatable, and rebuild brain resilience for the long term.

Sources

Dr. Jessica Knape https://www.healthspaninternalmedicine.com
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