More than 30 percent of North Americans over the age of 85 suffer from dementia. A study presented at the International Stroke Conference 2019 shows that having harmful bacteria in your colon increases risk for dementia (Scientific Reports, Jan 30, 2019;9(1008)). The study followed 128 outpatients, average age 74, visiting a memory loss clinic. Compared to those who did not have dementia, those with dementia had:
• markedly increased MRI evidence of brain bleeds and strokes
• markedly decreased colon levels of Bacteroides (enterotype I), which are healthful bacteria that decrease inflammation and help to lower high cholesterol and high blood pressure
• markedly increased harmful colon bacteria of enterotype III that increase inflammation
• increased stool concentrations of ammonia, indole, skatole, and phenol that are produced by harmful colon bacteria when they try to invade colon cells.

You have more than 100 trillion bacteria, of about 1000 different species, living in your colon. Many different studies have shown that what you eat determines which types of bacteria live in your colon and that certain types of bacteria can turn on your immune system to cause inflammation that increases risk for dementia (Curr Opin Pharmacol, 2017;37:87–92), as well as heart attacks, certain cancers, and auto-immune diseases (J. Alzheimers Dis, 2017;58:1–15).

You can encourage growth of healthful bacteria in your colon and discourage the harmful ones by:
• Eating lots of fruits, vegetables, whole grains, beans and nuts that are high in fiber, which fosters healthful colon bacteria (Food Funct, Apr 2016;7(4):1788-96)
• Restricting mammal meat (J Transl Med, Apr 8, 2017; 15: 73), refined carbohydrates (Diabetes Metab Syndr Obes, 2012;5:175-89), and fried foods (Amer Journal Clin Nutr, Aug 2014;100(2):667–675). See What You Eat Determines Your Microbiome

The Difference between Healthful and Harmful Colon Bacteria
Colon bacteria eat the same foods that you do. The healthful bacteria are content to eat what you eat, so they stay in your colon and do not try to cross into your cells and bloodstream, but the harmful bacteria try to find different food by invading the cells lining your colon. Your immune system tries to defend you by producing huge amounts of white blood cells and chemicals that work to destroy the invading bacteria by punching holes in their outer membranes and trying to kill them. This constant invasion of your colon cells by harmful bacteria can cause your immune system to stay overactive. When your immune system stays active all the time (inflammation), it uses the same cells and chemicals that attack invading germs to attack and damage your own cells to increase risk for dementia, heart attacks, certain cancers, and other diseases.

Evidence that Inflammation Increases Dementia Risk
Inflammation during midlife is associated with cognitive decline 20 years later (Neurology, Jan 13, 2019). A large prospective study showed that dementia is associated with anything that causes inflammation to damage blood vessels (diabetes, hypertension, smoking, lack of exercise, obesity), even in people who have not had a stroke (JAMA Neurology, August 7, 2017).

Another study showed that giving the healthful colon bacteria, Bifidobacterium breve, to people who suffered from mild cognitive impairment can improve mental functioning (J Prev Alz Dis, 2019;6(1):70-75). However, this may not be so easy to do because the types of bacteria that live in your colon are determined by what you eat and what you do so you cannot change colon bacteria permanently just by taking a dose of bacteria. To change the types of bacteria in your colon permanently, you may sometimes have to take antibiotics first to get rid of the harmful bacteria, and then create an environment in the colon that is conducive to growing healthful bacteria by making permanent changes in diet and lifestyle.

Four studies presented at the Alzheimer’s Association International conference in London (July 2018) showed that healthy older adults who followed a Mediterranean-type diet or the MIND diets reduced their risk for dementia by a third. These diets increase fish, fruits, vegetables, nuts, and whole grains, and restrict sugars and animal fats. See Diets Shown to Reduce Risk for Dementia

Heart Attack Prevention Measures Also Reduce Dementia Risk
Just about every risk factor for a heart attack has been shown to also increase risk for dementia and you can reduce your risk for suffering from dementia by up to 70 percent when you follow the healthful habits that help to prevent heart attacks (JAMA, Aug 21, 2018;320(7):657-664):
• eat an anti-inflammatory diet
• avoid smoking, alcohol, and obesity
• exercise, preferably every day
• treat diabetes, high blood pressure and high cholesterol
See Risk for Dementia Goes Down with Steps to Prevent Heart Attacks

My Recommendations
Since recent studies show that dementia may be influenced to a large degree by the types of bacteria living in your colon, I recommend eating the foods that encourage growth of healthful bacteria and discourage the harmful types. Harmful colon bacteria can cause inflammation that can increase your risk for dementia as well as for heart attacks, strokes and certain cancers. You can reduce inflammation by:
• eating a plant-based diet with a wide variety of vegetables, whole grains, beans, nuts and fruits
• restricting red meat, processed meats, fried foods, sugar-added foods and all drinks with sugar in them
• avoiding obesity
• avoiding smoke and alcohol
• exercising regularly
If you are not already eating a healthful plant-based diet and engaging in regular exercise, check with your doctor and then try to start a new diet and exercise program as soon as possible.

Checked 6/12/23