What is the relationship between Alzheimer’s and gut health?
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Our gut bacteria can influence the level of inflammation in our body. We know that inflammation can contribute to Alzheimer’s disease. Numerous recent studies show that dysbiosis (bacterial imbalance) in the human gut microbiota is associated with neurodegenerative diseases such as Alzheimer’s disease through neuroinflammatory processes along the microbiota-gut-brain axis. The gut microbiota influences brain health by increasing intestinal permeability, inflammation and secretion of toxins, short-chain fatty acids, which regulate numerous immune functions.
Increased intestinal permeability and toxic structures passing into the system also increase the permeability of the blood brain barrier and affect the pathogenesis of AD. Observational studies show that Alzheimer’s patients have reduced microbiome diversity, which may contribute to the development of the disease. Uncovering the genetic basis of microbiota diversity and its impact on Alzheimer’s may provide benefits that may reduce the individual’s risk of disease through lifestyle changes.
One group of studies found that mice with gut bacteria from Alzheimer’s patients performed worse on memory tests, did not develop as many new nerve cells in memory-related areas of the brain, and had higher levels of inflammation in the brain. The findings suggest that Alzheimer’s symptoms may be caused in part by abnormalities in the gastrointestinal tract. While many causes of Alzheimer’s processes in the brain are being studied, gut health potentially supports a complementary treatment that may be more easily influenced by drugs or dietary changes.
Alongside these studies, some very recent research is trying to identify gut bacteria suspected of playing a role in the development of Alzheimer’s disease. A team of researchers from the University of Nevada, USA, analysed 119 genera of bacteria in the gut, combing through data from a previous study involving thousands of participants. The team found that 10 bacterial genera may play a role in the development of Alzheimer’s. Of these 10 bacterial genera, 4 were linked to a version of a gene called apolipoprotein E (ApoE), which is thought to increase the risk of Alzheimer’s.
One of the bacterial strains was found to be associated not only with Alzheimer’s and the Apo version, but also with rheumatoid arthritis, atherosclerosis and Type-2 diabetes. This bacterial genus, which secretes metabolites that constitute risk factors for Alzheimer’s disease, is called Actinobacterium Collinsella. Future studies will continue on the balance of these and related bacteria, dietary options and pre-pro-postbiotics.
We have long known that genetics plays a critical role in the development of neurodegenerative diseases such as Alzheimer’s. In particular, a gene known as ApoE, which also plays a role in lipid metabolism, was investigated as a risk factor for Alzheimer’s disease and it was shown that one of the three variants of this gene, known as E4, poses a genetic risk for Alzheimer’s disease. In the light of new findings, it is thought that having at least one copy of E4 may also affect the composition of bacteria in the body.
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The new study published in BMC Medicine took the previous findings one step further. More than 60 thousand older adults’ health data were analysed. Among those whose diets were furthest from the Mediterranean diet, about 17 out of every 1,000 people were diagnosed with dementia in those 9 years. Among those whose food choices were most similar to the Mediterranean diet, only 12 out of every 1000 people were diagnosed with dementia.
It was stated that dementia symptoms occurred in 882 out of a total of 60,298 participants during the study period. The main message of this study was that even the possibility of dementia in individuals with higher genetic risk can be reduced by the Mediterranean diet. According to the research team, people close to the Mediterranean diet generally consume less red or processed meat. They also avoid sweets, pastries and sugary or sweetened drinks.
According to experts, other important ways to reduce the risk of Alzheimer’s are as follows:
- Getting enough sleep.
- Controlling blood pressure.
- Having healthy cholesterol and blood sugar levels.
To maintain a healthy brain as we age, the best available evidence suggests that we should stay physically fit, eat a balanced diet, maintain a healthy weight, not smoke, drink alcohol only within recommended limits, and keep blood pressure and cholesterol under control.
