As with anxiety, it’s not difficult to feel the connection between your gut and your memory. If you see an old partner who cheated on you, you might instantly become nauseous. If you drive down a street where you ate a delicious meal, you may start to salivate and your stomach might grumble. Given that your gut “remembers,” it should come as no surprise that it works hand in hand with your brain’s memory systems. The key to that connection lies in the chemicals that make your brain and body function, many of which are regulated by your gut.

For example, the stress hormone cortisol can disrupt your ability to recall long-term memories, and as we’ve covered before, your gut bacteria affect blood cortisol levels by regulating the hypothalamic-pituitary-adrenal axis.

That means that the wrong balance of gut bacteria can lead to a spike in cortisol, which in turn can put a damper on your ability to recall memories. Memory is also affected by levels of other neurochemicals, such as noradrenaline, serotonin, and dopamine.

For instance, we now know that noradrenaline enhances memory, especially when emotions are running high. And studies have identified a close association between a serotonin-dopamine imbalance and changes in brain tissue that lead to learning and memory impairment. Once again, all these neurochemicals are dependent upon gut bacteria to produce the necessary precursors to keep them at healthy levels.

The vagus nerve can enhance memory when stimulated because it connects to brain structures like the amygdala and hippocampus, which are central to memory formation. Since gut bacteria can change vagus nerve activation, that’s another way in which they affect your memory. The most telling sign that there is a strong connection between the gut and memory is that the composition of gut bacteria changes in patients afflicted with several memory-related diseases.

For instance, in Parkinson’s disease patients like Brian, there is a significant decrease—77.6 percent—of the specific gut bacterium Prevotellaceae compared to controls. And the microbiomes of Alzheimer’s patients have decreased Firmicutes, increased Bacteroidetes, and decreased Bifidobacterium. Sometimes the relationship can run the other way, with changes in gut bacteria altering the course of these diseases.

Rosacea is known primarily as a skin condition in which people blush or flush more easily, but rosacea patients also have a slightly increased risk of developing dementia, particularly Alzheimer’s disease. Changing gut bacteria can make a huge difference for rosacea patients. In 2009, Andrea Parodi and colleagues demonstrated that when you eradicate small-intestine bacterial overgrowth common in rosacea, the skin condition goes away.

This microbiome-based treatment can last up to nine months, and with the rosacea in remission, the risk of dementia is likely reduced. Researchers also believe that gut bacteria trigger metabolic processes and brain inflammation that impact memory, and they may also compromise blood flow in the brain. In addition, changes in gut bacteria may increase amyloid deposits, thereby contributing to Alzheimer’s disease.

Modification of the gut microbiome by diet or by using probiotics may offer new preventive and possible therapeutic options for Alzheimer’s. All this evidence points to the idea that we may be able to reduce the possibility of dementia by avoiding foods that compromise our gut bacteria and eating foods that enhance them.

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