– Over 55 million people around the world are estimated to be living with dementia, with Alzheimer’s Disease (AD) being the most common type.
– Although the exact causes of AD have yet to be fully established, amyloid and tau proteins are found to accumulate in the brain of patients with AD. Neuroinflammation is also often a key element in AD.
– Health of our gut microbiota is associated with AD. Harmful bacteria may worsen neuroinflammation, while metabolites from beneficial gut bacteria may help protect against it.
– Prebiotics could be used to enhance and regulate the health of the gut microbiota, thereby lowering the risk of developing AD.
Over 55 million people around the world are estimated to be living with dementia in 2020. This number is likely to double every 20 years, reaching a total of 78 million by the year 2030 [1]. The most common type of dementia is Alzheimer’s Disease (AD). We have discussed how dietary fiber may have effects on dementia based on a Japanese study done recently which found that a high intake of dietary soluble fiber is linked to a lower risk of developing disabling dementia [2]. Most prebiotics are dietary fibers. However, not all dietary fibers are prebiotics. Read on to find out more about the effects of prebiotics and gut microbiota on dementia and Alzheimer’s disease.
Our gut consists of trillions of such microorganisms including bacteria, viruses, fungi and protozoa species. This composition of microorganisms residing in our gut is collectively termed gut microbiota, which is unique to everyone. It varies due to several factors, such as environmental, lifestyle, dietary habits, and consumption of medications such as antibiotics [3].
This innate set of gut microbiota (the set that we are born with) is thought to be the most optimum for oneself. This optimum composition deteriorates as we age. Along with poorer modern-day diets lacking in prebiotics (i.e., food for the beneficial gut bacteria) as well as increased use of medications, the composition and amount of good gut bacteria decrease even faster.
Prebiotics are defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP) as a substrate that is selectively utilized by host microorganisms conferring a health benefit [4]. In loose terms, prebiotics are food for the beneficial gut bacteria in a process called fermentation. This feeding process produces metabolites such as short-chain fatty acids (SCFAs) which confer health benefits to us. One such health benefit could be healthy aging.
Although the exact causes of AD have yet to be fully established, it has been found that various types of proteins (e.g., amyloid and tau proteins) accumulate in the brains of patients with AD [5]. Neuroinflammation is also a key element in the accumulation of amyloid hence the progression of AD [6].
The health of our gut microbiota is associated with AD. The gut microbiota and the brain communicate bi-directionally, and this interaction has been termed the gut-brain axis [7]. Dysbiosis, which refers to an altered gut microbiota, has been associated with various neurodegenerative diseases including AD. Reduction in microbial diversity has been observed in patients with AD as compared to patients without [8].
Harmful gut bacteria may even produce amyloid peptides, which can enter the bloodstream due to increased gut permeability. These peptides can then cross the blood-brain barrier and accumulate amyloid in the brain, further exacerbating AD [9]. Metabolites produced from harmful bacteria can also worsen neuroinflammation in the brain, while metabolites (such as SCFAs) produced from beneficial gut bacteria may help protect against AD by inhibiting the aggregation of amyloid peptides and maintaining cognitive functions [9,10].
Prebiotics are food selectively utilized by beneficial gut bacteria. By taking prebiotics, we improve the health of our gut microbiota by allowing the beneficial bacteria to grow and proliferate, at the same time crowding out the harmful ones. This may help to ameliorate the risk factors of AD such as gut permeability, amyloid peptides, and systemic inflammation [9].
There is currently no cure for AD. Current evidence points to the importance of the gut microbiota as a modulator of neurodegenerative diseases such as AD. The gut microbiota serves as a promising therapeutic target for the prevention and treatment of AD. Prebiotics could potentially be used to enhance and regulate the health of the gut microbiota, thereby lowering the risks of neurodegenerative diseases.
Dietary Fiber and Its Links To Dementia
Prebiotic: Gut Microbiota, Gut Health, and Beyond
