In the scientific publication, “Alzheimer’s Disease and Gut Microbiota” published in the 59th volume, 10th issue of the Journal, Science China Life Science, (2016) authors Hu,X, Wang, T, and Jin, F present the possible links between gut microbes and Alzheimer’s Disease. This is a summary and interpretation of their findings.

THE ALZHEIMER’S CRISIS:
Alzheimer’s Disease is the most common form of dementia affecting memory, thinking and behavior. It is a progressive disease, increasing in risk with age. Current knowledge is that it is irreversible.

This topic is “near and dear” to my heart. When I was a child, my Great Uncle committed suicide because he found out that he had Alzheimer’s Disease. At the time, my viewpoint of this tragedy was that of a child. I didn’t understand why he chose to do that. Now that I’m an adult and I understand more, it breaks my heart to know how he must have been feeling to make such a decision.

I know he is not alone. According to the Alzheimer’s Association:

• Currently, 5 million Americans live with Alzheimer’s Disease (AD) in the U.S.
• This number could be 16 million by 2050.
• AD is the 6th leading cause of death, more than breast and prostate cancers combined.

MAYBE GUT BACTERIA?
In the past, the understanding of Alzheimer’s disease has focused on genetics and environment (lifestyle, hazardous materials, etc…). Scientists are now starting to question if the gut microbes play a role, as well. The rapid increase in Alzheimer’s diagnoses in recent years suggest that something more than just mom and dad’s genes are at play. In 2003, the Human Genome Project was completed. The result of the project was that we discovered the exact DNA sequence of a human. It was determined that humans have approximately 30,000 genes (rice has 46,000). So, how are humans so complex? Our DNA contains less genes than a rice plant!? The answer lies in our gut (intestines). The average human gut contains around a quadrillion (1014) bacterial cells, that hold about 4 million genes! These genes code for products that influence everything from our health to our thinking and behavior.  So, is this starting to make sense? Potentially four million genes plus 30,000 genes equals a complex organism!

BLOOD-BRAIN BARRIER
At birth, and even before, bacteria and other microbes begin to enter your body and make a home. Your gut is a prime destination. The microbes that live in your gut during childhood are essential to your brain development. In fact, which microbes live there and how many can impact your physical and mental health for the rest of your life. We now know that gut microbes influence the maturation and function of cells that make up your blood-brain barrier (BBB). This is the barrier that is supposed to protect your brain from outside things, like virus, bacteria and other molecules.

LEAKY BRAIN
In the past, scientists thought that the BBB was completely leak-proof. We now know that this is not the case. A recent study in germ-free mice showed that without gut microbes, the mice had altered cell numbers (less) and more immature cells in their BBB. This is now called “leaky brain.” Things could pass through that should not pass through. In the mouse study, this leaky brain lead to neuro-degenerative diseases, including Alzheimer’s disease.  How did this protective barrier become leaky? It’s possible that inflammation in the body, as a result of leaky gut, impacts how well the blood-barrier functions.

LEAKY GUT
Now, you may have already heard of leaky gut. The tube that is your gastrointestinal (GI) tract is lined with one layer of skin cells. Think of them like the toy snap cubes children use to learn math. They are linked together by snaps, called tight junctions. When these snaps are compromised (un-snapped) a hole forms between two cells. Now, the stuff inside your intestines (bacteria, food, and more) can “leak” out into your bloodstream. This is called “leaky gut.” Your blood is full of immune cells (little soldiers) that are on the hunt for anything that is not human. When they “see” the leaking bacteria, or food particles, they mount a response. That response is inflammation. If you don’t repair the holes, the inflammation never stops. People live for years and years with inflammation. Years and years of inflammation could lead to diseases, like autoimmunity, diabetes, high blood pressure, liver cirrhosis, Parkinson’s, dementia and even more.

ALZHEIMER’S POSSIBLE CONNECTION TO LEAKY GUT
Most of the bacteria in your gut is what scientists call, “Gram negative.” This type of bacteria has an outer layer called a lipopolysaccharide (LPS). When it leaks out of your gut, this LPS layer really gets your immune system “freaking out”, causing inflammation. Studies show that people with Alzheimer’s disease have 3 times higher levels of LPS in their blood than healthy people!  How did the bacteria LPS get in their blood? Maybe, they have leaky gut. Well, if they have leaky gut, do you think they might have leaky brain? A protein called A-beta collects in the brains of AD patients. More goes in than comes out. This protein promotes plaque development in the brain. A study in mice shows that when bacterial LPS is injected into the body, the blood-brain barrier lets more of this A-beta protein in, and less of it out. Other studies of this type show this method leads to serious memory problems in the mice.

ANTIBIOTICS & STRESS
I know you’re thinking, “Yikes! I don’t want to have leaky gut. How do I prevent it?” Stress, infections and antibiotics all destroy gut microbes. The amount and types of microbes that they destroy depend on the level of stress, type of infection and type of antibiotics taken. In one study with mice, when they were treated with a “mild” antibiotic, their stress hormone increased, anxiety behavior increased, and memory decreased. When given the Probiotic, Lactobacillus, all of these abnormalities listed were restored. That’s the good news with Ampicillin, the damage is reversible. That is not the case with all of the antibiotics, though.

SUGAR
Some gut microbes are good for us and some gut microbes are bad for us. The bad ones contribute to leaky gut, and the resulting inflammation. The good ones protect you, fight off the bad ones, and result in overall health. You can control the types of microbes living in your gut by your long-term diet choices and your lifestyle. For example, the bad yeast (one of the causes of common yeast infection), Candida albicans, loves to grow on SUGAR! What do Americans love to eat? SUGAR! What foods contain a lot of sugar, besides the obvious? Breads, alcohol, juices and many more all contain large amounts of sugar. So, if these items are a regular part of your diet then, chances are pretty good that you have an overgrowth of yeast in your gut. An easy test is to ask yourself, “Do you crave sugar?” It is the yeast in your gut sending signals to your brain to crave the sugar (that’s a topic for another day). Yeast overgrowth is involved in leaky gut.

GET DIRTY
So, now that we’re all on the same page and this just got “real,” let’s wrap things up with a final point. In 1989, the scientific community came out with the “hygiene hypothesis” for Alzheimer’s Disease. They may be exactly right. The hypothesis stated that increased sanitation (washing food, hands and everything else) and a decreased exposure to microbes early in life (prime time for immune system development) can lead to Alzheimer’s later in life. There are even studies which show that countries with lower sanitation have lower numbers of Alzheimer’s disease in their populations and the opposite is true for well-sanitized countries, like the United States. In fact, they show that farm living, having more siblings, having pets in the house, and later birth order all reduce your risk for AD. All of these situations expose you to more germs while you’re young. You get more of the good bacteria in your gut! This develops your immune system in a normal fashion so that it does not over-react as is the case with allergies, autoimmunity and more.

Is all hope lost? You already have allergies, autoimmunity or more. No, hope is not lost! The best news is, the immune cells that keep things calmed down and promote “immune tolerance” in your body are called T regulatory cells. Studies show that a constant, low-level exposure to good microbes can cause baby T cells to turn into these protective, T regulatory cells during the course of your ENTIRE LIFE! So, it’s never too late to start eating right, taking probiotics, prebiotics and cleaning up your diet.

If you would like to read the original publication that this blog was based on, check it out here: www.ncbi.nlm.nih.gov/pubmed/27566465