Does Alzheimer’s Disease Start In The Gut Microbiome?

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Welcome to my blog post ‘Does Alzheimer’s Disease Start In The Gut Microbiome?’.

You may also be interested in the section of my blog dedicated to brain health, click here, in particular:

Does Alzheimer’s Start In The Gut?

Multiple experimental and clinical studies revealed the role of gut microbiota in cognition, and its dysbiosis associated with aging leads to neurodegeneration.

Gut microbiome composition acts as a significant influencing factor in several age related neurological disorders. Several extrinsic factors (diet, lifestyle, and infection) and intrinsic factors (genetics, metabolites, immune response, and hormones) influence the composition of the gut microbiome, which in turn produces neurotransmitters or ‘neuromodulators’ in the gut that regulate the central nervous system.

Aging causes alteration in gut bacteria composition with an increase in pro-inflammatory bacteria and a general decrease in the distribution of anti-inflammatory bacteria. This may induce local and systemic inflammation leading to enhanced ‘leakiness’ of the gut lining, impairing blood brain barrier function, and promoting neuroinflammation (brain inflammation).

So to answer this question, and to be balanced in my response – Alzheimer’s disease doesn’t necessarily start in the gut but imbalances in the gut most certainly contribute to the condition.

IBS And Alzheimer’s Disease

As a result of this, we do want to be particularly mindful if we suffer with poor gut health. Just thinking about this logically, individuals with IBS often are found to have:

  • Small intestine bacterial overgrowth.
  • Intestinal permeability (leaky gut).
  • Imbalances in the microbiome of the large intestine.
  • Altered immune and inflammatory status.

Hypothesis based on these reports is gut barrier dysfunction leads to inflammation followed by dysbiosis, enhancing the level of calprotectin contributing to amyloid fibril formation in the gut and the brain leading to microglial cell activation and neurodegeneration.

These are all things that are being discussed in the Alzheimer’s research that is focusing on the role of the gut in the condition.

This is NOT to say that those with IBS will develop Alzheimer’s but it may increase the risk in a subset of individuals who also have other risk factors for Alzheimer’s.

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What Bacteria Cause Alzheimer’s?

There is not a single bacteria that has been associated with Alzheimer’s and in fact research has discussed not only bacteria, but also viruses, fungi and parasites that might be associated with the condition.

Post-mortem of Alzheimer’s disease brains showed multiple pathogens such as bacteria (Borrelia burgdorferi), viruses (herpes simplex virus type 1), fungi, and protist parasites depicted the fact that Aβ peptide is part of a generalised innate immune response that is not specific to a particular microorganism (1).

Also a lot of the research discusses more generalised imbalances in the gut microbiome potentially contributing to Alzheimer’s.

Alteration in gut microbiome composition enhances the release of metabolites called ‘lipopolysaccharides’ (LPSs) and amyloids, which may contribute to the pathogenesis of Alzheimer’s, especially during ageing when both the gut lining and blood brain barrier become more permeable (‘leaky’) (1).

It has been proposed that LPS and amyloids may directly pass through a compromised GI tract or BBB.

For example, fecal microbiota studies of AD and non-AD patients showed a decreased level of Firmicutes and Bifidobacterium, and a rich source of Bacteroidetes.

Recent studies revealed that H. pylori infection in AD and PD patients enhanced the severity of the disease.

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Do Probiotics Help Alzheimer’s?

As ageing together with poor diet and gut-derived inflammatory response due to dysbiosis contributes to the pathogenesis of Alzheimer’s, modification of gut microbial composition by uptake of probiotic-rich food can act as a preventive/therapeutic option for AD (1).

The future is promising in this regard. Overall the results of in vivo studies in model animals showed that the “probiotic supplementation ameliorates the AD-associated physical, psychological, and cognitive health issues“.

In a human study (1) supplementation of probiotic milk (200 ml/ day) containing a mixture of probiotic strains (Lactobacillus acidophilus, L. casei, Bifidobacterium bifidum, and L. fermentum) for 12 weeks improved the following in AD patients:

  • The mini-mental state examination (MMSE) score
  • Malondialdehyde (MDA)
  • The inflammatory marker called serum high sensitivity C-reactive protein (hs-CRP)
  • Homeostatic model of assessment for insulin resistance (HOMA-IR) score
  • Quantitative insulin sensitivity check index (QUICKI) value
  • Triglycerides (TG)

The results suggested that supplemented probiotic milk improved the cognitive status and insulin metabolism in AD patients without interfering with the lipid profile, antioxidant, and inflammatory system.

In another study (1) the supplementation of probiotic mix (L. casei W56, L. acidophilus W22, B. lactis W52, L. paracasei W20, L. plantarum W62, Lactococcus lactis W19, B. lactis W51, B. bifidum W23, and L. salivarius W24) for 28 days improved the gastrointestinal health of AD patients.

In this study notably the level of zonulin (a marker for leaky gut) was decreased after the probiotic intervention compared to the baseline value.

The results showed that the intervention of multispecies probiotic preparation might alter the microbiome, and influence the tryptophan metabolism, and improve the intestinal permeability in AD patients.

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Which Probiotics Are Best For Alzheimer’s Disease?

At present, research is in it’s early days and we are still learning the best ways forward with this. Recommendations must start with consuming enough probiotic and prebiotic foods, getting adequate exercise, managing our stress, sleeping enough, focusing on our relationships and community, reducing toxic exposures. These have all been discussed in the research of Alzheimer’s.

  • Probiotic foods/drinks: Kombucha, kefir, sauerkraut, kimchi, live yoghurt.
  • Prebiotic foods: onions, garlic, asparagus, artichokes, wheat (if tolerated), olives and many others

Researchers have turned their attention towards developing novel therapeutics such as psychobiotics (microbiota, which supports good mental health) for the treatment of neurological disorders related to cognitive function and gastrointestinal disorders (1).

Summary Of ‘Does Alzheimer’s Disease Start In The Gut?’

  • The gut microbiome may contribute to neurodegenerative conditions such as Alzheimer’s disease.
  • Leaky gut is one of the mechanisms behind this.
  • Probiotics may be helpful in a. subset of people with the condition – and certainly focusing on optimising gut health is away to reduce our risk of developing the condition.
  • A holistic approach, focusing on many areas os lifestyle is by far the most important approach to ageing well.

References For ‘Does Alzheimer’s Disease Start In The Gut?’:

  1. Role of gut-brain axis, gut microbial composition, and probiotic intervention in Alzheimer’s disease: click here.
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