Stress Shrinks Your Brain and Impairs Memory

Written by Dr. Joseph Mercola

Story at-a-glance -

  • Research has linked chronic stress with brain shrinkage, working memory impairment and an increased risk for early onset of Alzheimer’s disease
  • Having elevated blood levels of the stress hormone cortisol can impair your thinking skills and memory over time. A previous study suggests elevated cortisol affects your memory by causing a gradual loss of synapses in your prefrontal cortex
  • Research suggests you can slow down the rate of cognitive decline by 75 percent by restoring your hearing with hearing aids, and by 50 percent by restoring vision through cataract surgery
  • Among the most valuable dementia prevention strategies is a cyclical ketogenic diet, as it optimizes mitochondrial function and supports healthy brain function
  • Other important lifestyle factors that influence your dementia risk include sleep, physical fitness and exposure to electromagnetic fields

Studies have found strong links between acute and/or chronic stress and a wide variety of health issues, including your brain function and risk for dementia. For example, animal research1 published in 2014 reported that elevated levels of stress hormones can speed up short-term memory loss in older adults by inducing structural changes in the brain.

The findings indicate that how your body responds to stress may be a factor that influences how your brain ages over time. Previous research has also linked chronic stress with working memory impairment2 and an increased risk for early onset of Alzheimer's disease.3

Fortunately, there's compelling research showing your brain has great plasticity and capacity for regeneration, which you control through your diet and lifestyle.

Based on the findings linking dementia with chronic stress, having effective tools to address stress can be an important part of Alzheimer's prevention, not to mention achieving and maintaining optimal health in general.

Stress Impairs Cognition and Memory, Recent Research Shows

Most recently, researchers warn that having elevated blood levels of the stress hormone cortisol can impair your thinking skills and memory over time.4,5,6,7 The researchers used the government-sponsored Framingham Heart Study database to identify more than 2,200 people who did not have any signs of dementia, and followed them for eight years. As reported by The New York Times:8

"Researchers gave tests for memory, abstract reasoning, visual perception and attention to 2,231 people, average age 49 and free of dementia. They recorded blood levels of cortisol and did MRI examinations to assess brain volume.

The study,9 in Neurology, controlled for age, sex, education, body mass index, blood pressure and many other variables, and found that compared with people with average levels of cortisol, those with the highest levels had lower scores on the cognitive tests.

In women, but not in men, higher cortisol was also associated with reduced brain volume. There was no association of the lowest cortisol levels with either cognitive test scores or brain size."

A significant limitation of the study is the fact that blood levels of cortisol were only checked once, at the end of the study, and may therefore not be representative of people's long-term exposure to this stress chemical.

Still, a number of other studies have reported similar findings, so the link between stress and cognitive decline certainly appears to be real. Lead author Dr. Justin Echouffo-Tcheugui, assistant professor of medicine at Johns Hopkins School of Medicine, commented on the findings:10

"Our research detected memory loss and brain shrinkage in middle-aged people before symptoms started to show in ordinary, daily activities.

So, it's important for people to find ways to reduce stress, such as getting enough sleep, engaging in moderate exercise, incorporating relaxation techniques into their daily lives, or asking their doctor about their cortisol levels and taking a cortisol-reducing medication if needed. It's important for physicians to counsel all people with higher cortisol levels."

Stress Hormones Have a Corrosive Effect in Your Brain

When you're stressed, your cortisol rises and, together with adrenaline, triggers your body's fight-or-flight response. Cortisol also increases the glucose level in your bloodstream and temporarily enhances your brain's use of that glucose, while simultaneously suppressing bodily functions deemed irrelevant during an emergency, such as digestion.

While this cascade of biochemical effects is beneficial when you're in immediate physical danger, cortisol has a corrosive effect that, over time, actually wears down the synapses responsible for memory storage and processing. This was demonstrated in the 2014 animal study11 mentioned earlier.

According to that study,12 elevated levels of cortisol affect your memory by causing a gradual loss of synapses in your prefrontal cortex, the brain region associated with short-term memory. As noted by the authors:

"Short-term increases in cortisol are critical for survival. They promote coping and help us respond to life's challenges by making us more alert and able to think on our feet.

But abnormally high or prolonged spikes in cortisol — like what happens when we are dealing with long-term stress — can lead to negative consequences that numerous bodies of research have shown to include digestion problems, anxiety, weight gain and high blood pressure."

While the authors of the Neurology study state that it is "premature to consider intervention" based on their findings,13 they suggest that lowering your cortisol may be a beneficial first step. The 2014 study authors also suggested you may be able to protect your future memory function by normalizing your cortisol levels.

Such intervention would be particularly beneficial for those who are at high risk for elevated cortisol, such as those who are depressed or are dealing with long-term stress following a traumatic event.

Stress May Trigger Clinical Onset of Alzheimer's

Other scientific findings have linked stress and severe dementia. Argentinian research14 presented at the World Congress of Neurology in 2013 suggests stress may actually act as a trigger for the onset of Alzheimer's disease, as nearly 3 in 4 Alzheimer's patients (72 percent) had experienced severe emotional stress during the two years preceding their diagnosis.

In the control group, only 26 percent, or 1 in 4, had undergone major stress or grief. Most of the stresses encountered by the Alzheimer's group involved:

  • Bereavement — death of a spouse, partner, or child
  • Violent experiences, such as assault or robbery
  • Car accidents
  • Financial problems, including "pension shock"
  • Diagnosis of a family member's severe illness

According to lead author Dr. Edgardo Reich:15

"Stress, according to our findings, is probably a trigger for initial symptoms of dementia. Though I rule out stress as monocausal in dementia, research is solidifying the evidence that stress can trigger a degenerative process in the brain and precipitate dysfunction in the neuroendocrine and immune system. It is an observational finding and does not imply direct causality. Further studies are needed to examine these mechanisms in detail."

Vision and Hearing Problems Also Linked to Dementia

Aside from managing daily stresses, protecting your vision and hearing are other important factors that can influence your dementia risk. In fact, recent research16 suggests you can actually slow down cognitive decline by restoring your hearing and/or vision, and by a significant degree.

Lead author Dr. Asri Maharani, a researcher at the University of Manchester in the division of neuroscience and experimental psychology, told NPR,17 "We found the rate of cognitive decline was slowed by 75 percent following the adoption of hearing aids. It is a surprising result."

While the researchers were surprised by the findings, it does make sense. As noted by Dina Rollins, an audiologist who was not involved in the study, "Stimulating your ears stimulates the nerves that stimulate your brain," so by restoring hearing, you're "giving your brain what it needs to make sense of what you're hearing."

Another possible reason for this link has to do with the fact that hearing loss leads to social isolation, which has also been shown to speed cognitive decline and raise your risk of dementia. A related study18 by the same research group shows cognitive decline is also slowed by restoring vision. Here, Maharani's team found that cataract surgery slowed the rate of cognitive decline by 50 percent.

Ketogenic Diet Protects Against Dementia

As mentioned, there's good news in all of this, and it's that your brain has a natural capacity for regeneration and rejuvenation. Among the most valuable dementia prevention strategies is a cyclical ketogenic diet described in my book, "Fat for Fuel" and many other articles. If you're new to this topic, see "Burn Fat for Fuel" or "A Beginner's Guide to the Ketogenic Diet" for an introduction.

In short, a ketogenic diet, being high in healthy fats and low in net carbohydrates, allows your body to start burning fat as its primary fuel and results in the creation of ketones. And, compared to glucose, ketones:

  • Burn more efficiently
  • Are a superior fuel for your brain
  • Generate fewer reactive oxygen species and less free radical damage
  • Influence DNA expression to increase detoxification and antioxidant production
  • Inhibit inflammation

Recent research19,20,21,22,23 shows a ketogenic diet improves neurovascular integrity and function and clearance of amyloid-beta (a main component of the plaque that accumulates in the brains of those with Alzheimer’s disease) — in part by improving the gut microbiome — and neurovascular function plays a major role in cognitive capability.

More specifically, poor neurovascular function is strongly associated with loss of language, memory and attention, while reduced cerebral blood flow raises your risk for depression, anxiety and dementia. Impaired blood-brain barrier function has also been linked to brain inflammation, dysfunction of synapses, impaired clearance of amyloid-beta plaques, psychiatric disorders and dementia.24

According to the authors, "Our findings suggest that ketogenic diet intervention started in the early stage may enhance brain vascular function, increase beneficial gut microbiota, improve metabolic profile, and reduce risk for Alzheimer's disease."

High-Sugar Diet Is a Recipe for Dementia

It's important to realize the adverse impact sugar has on your brain. A high-sugar diet triggers insulin resistance, and there's a very strong link between insulin resistance and Alzheimer's.25 For example, a longitudinal study26 published in the journal Diabetologia in January 2018, found that the higher an individual's blood sugar, the faster their rate of cognitive decline.

Even mild elevation of blood sugar and mild insulin resistance are associated with an elevated risk for dementia.27,28 Research29 published in 2013 showed that sugar and other carbohydrates disrupt your brain function primarily by shrinking your hippocampus, a brain region involved with the formation, organization and storage of memories.

The authors suggest that “strategies aimed at lowering glucose levels even in the normal range may beneficially influence cognition in the older population.” A similar study30 published in 2014 found that Type 2 diabetics lose more gray matter with age than expected, and this brain atrophy also helps explain why diabetics have a higher risk for dementia, and have earlier onset of dementia than nondiabetics.

As noted by Dr. Sam Gandy, director of the Center for Cognitive Health at Mount Sinai Hospital in New York City, these findings “suggest that chronic high levels of insulin and sugar may be directly toxic to brain cells” and that “this would definitely be a potential cause of dementia."31

Perhaps one of the most striking studies32 on carbohydrates and brain health revealed high-carb diets increase your risk of dementia by 89 percent, while high-fat diets lower it by 44 percent.

Sleep, Exercise and EMF Avoidance Are Other Key Dementia Prevention Strategies

Aside from stress and diet, three other lifestyle areas that play important roles in the development of dementia are sleep, physical fitness and exposure to electromagnetic fields (EMFs), the influence of which are summarized below.

Sleep — Wakefulness is associated with mitochondrial stress. Without sufficient sleep, neuron degeneration sets in, which can lead to dementia.33,34,35 In fact, sleep deprivation is a risk factor for severe dementia, and animal research36 reveals inconsistent, intermittent sleep results in considerable and irreversible brain damage.

Research published in the journal Neurobiology of Aging37 suggests people with chronic sleep problems also develop Alzheimer's disease sooner than those who sleep well.

Your blood-brain barrier becomes more permeable with age, allowing more toxins to enter.38 This, in conjunction with reduced efficiency of the glymphatic system due to lack of sleep, allows for more rapid damage to occur in your brain and this deterioration is thought to play a significant role in the development of Alzheimer's.

Exercise — Recent research39 found women with the highest cardiovascular fitness had an 88 percent lower risk of dementia than those with moderate fitness. Even maintaining average fitness is worthwhile, as women with the lowest fitness had a 41 percent greater risk of dementia than those of average fitness.

Electromagnetic field (EMF) exposure — Microwaves emitted from cellphones, Wi-Fi routers, computers and tablets (when not in airplane mode) harm your brain by increasing intracellular calcium through the voltage gated calcium channels (VGCCs) in your cells.

The tissues with the highest density of VGCCs are your brain, the pacemaker in your heart and male testes. Once VGCCs are stimulated, they trigger the release of neurotransmitters, neuroendocrine hormones and highly damaging reactive oxygen species, significantly raising your risk of anxiety, depression and neurodegenerative diseases like Alzheimer's.40

Basic prevention strategies include turning your Wi-Fi off at night, not carrying your cellphone on your body and not keeping portable phones, cellphones and other electric devices in your bedroom. To learn more, see my interview with professor Martin Pall. A more extensive list of prevention strategies to minimize your EMF exposure can be found in "Electromagnetic Radiation Specialist Reveals the Hidden Dangers of Electric Fields."

While I believe these are among the most important prevention strategies, there are of course many other factors that can come into play. To learn more about the prevention and reversal of cognitive decline, see my interview with Dr. Dale Bredesen, director of neurodegenerative disease research at the University of California, Los Angeles School of Medicine, whose unique ReCODE (Reversal of Cognitive Decline) program offers hope for many.

In 2014, Bredesen published a paper that demonstrates the power of lifestyle choices for the prevention and treatment of Alzheimer's. By leveraging 36 healthy lifestyle parameters, he was able to reverse Alzheimer's in 9 out of 10 patients. This included the use of exercise, ketogenic diet, optimizing vitamin D and other hormones, increasing sleep, meditation, detoxification and eliminating gluten and processed food.

In all, Bredesen has identified 150 different variables that can have a significant influence on Alzheimer's, but at the heart of it all is mitochondrial dysfunction, and one of the pronounced health effects of a cyclical ketogenic diet is the optimization of mitochondrial function. Not surprisingly, Bredesen's ReCODE Protocol also includes nutritional ketosis. You can download Bredesen's full-text case paper41 online, which details the full program.

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