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Is Oral Bacteria a Risk Factor for Alzheimer's?

Is Oral Bacteria a Risk Factor for Alzheimer’s?

In a new review, scientists have added novel information to the growing body of research suggesting that mouth infections may play a role in late-onset Alzheimer’s disease (AD). The researchers analyzed more than 200 studies that had investigated the link between infections of the mouth and AD. They discovered new oral microbial culprits that had somehow previously missed the spotlight.

Alzheimer’s researchers and doctors have been eager to discover a biomarker for the disease, a condition that plagues nearly 44 million people worldwide. Having spent decades studying how oral microorganisms invade local tissue and systematically destroy it, University of Oslo Professor Ingar Olsen was compelled to draw upon his studies and apply them to AD research.

He conducted the research with one of the foremost experts on the topic — Sim K. Singhrao, a senior research fellow at the University of Central Lancashire’s Oral & Dental Sciences Research Group, UK.

Their review is published in the Journal of Oral Microbiology. The paper addresses the “plausible aetiology of late-onset AD being an oral infection.”

It is well known that inflammation of the brain is a characteristic feature of AD. In recent years, scientists have been searching for potential root causes, many zeroing in on “peripheral infections” such as those that originate in the mouth.

Researchers have well established that many bacteria in the mouth, particularly in people with gum disease, find their way into the host bloodstream. If they pass through the blood brain barrier, any number of them could be implicated in the Alzheimer’s enigma, says Olsen.

In poring over the research for the review, Olsen — who has spent decades identifying the hundreds of bacteria species that comprise the oral micro biome — was struck by one particular observation.

“I was amazed that so much of the research to date has been focused on a couple of groups of bacteria, namely spirochetes and Porphyromonas gingivalis,” said Olsen, “when there are well over 900 different bacteria in the oral cavity.

“I thought, this can’t be the entire story!”

“Even oral Candida and herpes virus could possibly cause the inflammation in the brain that we see in Alzheimer’s patients,” said Olsen.

Candida, a typically harmless fungus found in the mouths of half the world’s population, can become treacherous and lead to infection if it enters the bloodstream. And herpes simplex virus is present in more than 70 percent of people over 50 years old. It lies dormant in the peripheral nervous system and is periodically reactivated in the brain.

Of Candida, Olsen and Singhrao wrote in the paper: “With a growing population of elderly, severe systemic fungal infections have increased dramatically in this age group during the last 30 years. Oral yeasts can be found in periodontal pockets, in root canals, on the mucosae, and underneath dentures.”

“Fungal molecules including proteins and polysaccharides were detected in peripheral blood serum, and fungal proteins and DNA were demonstrated by PCR in brain tissue of AD patients.”

PCR (polymerase chain reaction) is a laboratory technique used to amplify or copy a specific DNA target among a mixture of DNA molecules.

Olsen says he is eager to explore these new potential culprits.

Source: Co-Action Publishing

Elderly woman worried about mouth infection photo by shutterstock.

Is Oral Bacteria a Risk Factor for Alzheimer’s?

Traci Pedersen

Traci Pedersen is a professional writer with over a decade of experience. Her work consists of writing for both print and online publishers in a variety of genres including science chapter books, college and career articles, and elementary school curriculum.

APA Reference
Pedersen, T. (2018). Is Oral Bacteria a Risk Factor for Alzheimer’s?. Psych Central. Retrieved on September 25, 2020, from
Scientifically Reviewed
Last updated: 8 Aug 2018 (Originally: 20 Sep 2015)
Last reviewed: By a member of our scientific advisory board on 8 Aug 2018
Published on Psych All rights reserved.