Chronic cannabis smokers harbored elevated levels of the oral bacterium Actinomyces meyeri, which when fed to mice for six months decreased activity, increased brain macrophage infiltration, and boosted amyloid-beta production.
Neuroscience researchers, oral health professionals, and anyone interested in how cannabis smoking might affect the brain through unexpected pathways.
First study linking cannabis-associated oral bacteria to brain amyloid-beta production
What the researchers found
Cannabis smokers showed oral microbial dysbiosis with increased Streptococcus and Actinomyces and decreased Neisseria. Mice orally exposed to the cannabis-enriched bacterium Actinomyces meyeri for six months showed decreased global activity, increased macrophage brain infiltration, and increased beta-amyloid 42 protein production.
Why it matters
This is the first study to connect cannabis-associated changes in oral bacteria to potential neurological consequences, suggesting a novel pathway by which chronic cannabis smoking might affect brain health.
The numbers in context
16 cannabis smokers vs 27 controls; mice inoculated twice weekly for 6 months; Actinomyces meyeri enrichment inversely associated with age of first cannabis use; increased beta-amyloid 42 production in mouse brains
How the study worked
Researchers compared saliva microbiomes of 16 chronic cannabis smokers with cannabis use disorder and 27 non-smoking controls using 16S rRNA sequencing. Then mice were orally inoculated with Actinomyces meyeri, Actinomyces odontolyticus, or Neisseria elongata twice weekly for six months to test functional effects.
What this study cannot tell us
Very small human sample (16 vs 27). Mouse model may not replicate human oral-brain pathways. Cannot determine whether cannabis itself or combustion byproducts caused the microbial changes. No control for tobacco co-use.
How to read the evidence
Novel translational study combining human microbiome data with animal experiments, but very small human sample and animal-to-human extrapolation limits conclusions.
When this study was published
Published in 2021.
The bigger picture
The oral microbiome-brain axis is an emerging area of research. This study adds cannabis smoking as a factor that may reshape oral bacteria in ways that have downstream neurological consequences, though the pathway from human observation to mouse experiment needs further validation.
Questions still open
- Do non-smoked forms of cannabis produce the same oral microbial changes? Is this pathway relevant to human neurodegenerative disease risk? Could oral hygiene interventions mitigate these effects in cannabis smokers?
Common questions
Does this mean cannabis causes Alzheimer's?
Was it the cannabis or the smoking?
Read the original research
Chronic cannabis smoking-enriched oral pathobiont drives behavioral changes, macrophage infiltration, and increases β-amyloid protein production in the brain.
EBioMedicine, 74, 103701
Citation
Luo, Zhenwu; Fitting, Sylvia; Robinson, Catrina; Benitez, Andreana; Li, Min; Wu, Yongxia; Fu, Xiaoyu; Amato, Davide; Ning, Wangbin; Funderburg, Nicholas; Wang, Xu; Zhou, Zejun; Yu, Xuezhong; Wagner, Amanda; Cong, Xiaomei; Xu, Wanli; Maas, Kendra; Wolf, Bethany J; Huang, Lei; Yu, Jeremy; Scott, Alison; Mcrae-Clark, Aimee; Hamlett, Eric D; Jiang, Wei. (2021). Chronic cannabis smoking-enriched oral pathobiont drives behavioral changes, macrophage infiltration, and increases β-amyloid protein production in the brain.. EBioMedicine, 74, 103701. https://doi.org/10.1016/j.ebiom.2021.103701
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