The Relationship Between Stress and Alzheimer’s Disease

Stress markedly alters brain activity. It is thought that the human brain actually does not have a “stress response” but rather only a danger response.  The purpose of this response is to focus all brain resources only on the danger at hand.  While this serves to help with survival, it is counterproductive for normal function. While this response helped with survival for millions of years, it may be causing us problems in our modern environment as this reaction is also triggered by psychosocial stress.  Danger tended to be infrequent and brief.  Stress in contrast, is frequent and ongoing for many.

It seems this hyperactivity in the frontal brain attention area comes at the expense of a lot of other brain functions, some important in processing memory.  While we develop intense memory of the dangerous situation, we do not process everything else occurring at the same time.  No harm is done during 10 minutes of danger but when the same reaction is triggered over days by psychosocial stress, normal memory processing is sacrificed at the expense of focus on the stress.

There has been demonstration that exposing adults to higher levels of short-term stress impairs important memory circuits.  A recent study compared processing of long-term and working memory during higher stress as measured by a test called “Stress and Adversity Inventory”.(1)  Both forms of memory processing were impaired during higher stress scores.

The key question has been does this short-term suppression of memory eventually lead to ongoing memory dysfunction with chronic stress.  A study of 1415 women over 35 years of age has answered that question.(2)  Subjects were evaluated for intervals of stress over three decades during middle age.  Subjects were separated into groups based on having significant stress during none, one, two or all three decades.  Compared to those who experienced no sustained stress, there was an increasing relationship between the number of stressful decades and the risk of developing Alzheimer’s.  The increased risks of developing the disease were 9%, 82% and 183% respectively for 1, 2 or 3 decades of higher stress.

The answer to the question, does memory suppression associated with sustained stress eventually translate to increased risk of Alzheimer’s, appears to be an emphatic yes. Often stress is unavoidable such as with the serious illness of a family member.  Another recent study has suggested the mechanism of this relationship.(3)  An important driver of Alzheimer’s disease is chronic inflammation.  It is typically triggered by toxicities such as with heavy metals, diet, omega-3 fatty acid insufficiencies and chronic infections such as Lyme.  Stress is also a potent driver of chronic inflammation.

This recent study looked at a marker of chronic inflammation, blood levels of IL-6 in one of the most stressed populations, caregivers of a family member with Alzheimer’s.  Subjects not under stress from caregiving were used as the control group.  The first observation was that IL-6 and thus inflammation increased 33% between 55 and 95 years of age in the control group.  This increased tendency for inflammatory levels to elevate with aging has been termed “inflammaging” and is thought to be one of the drivers of the increased degenerative disease risk with progressive age.

The second observation was that the increased levels of IL-6 over the same age transition was 395%, or 10 times greater in the stressed caregivers.  Both age and sustained stress are risk factors for Alzheimer’s disease.  The former is unavoidable, while the second may be in some circumstances.  Some stress is avoidable, while other stress circumstances are not.  In those with unavoidable stress the importance of an otherwise anti-inflammatory lifestyle is paramount.  This involves careful attention to diet, weight, sleep and other factors which are known to contribute to chronic inflammation.

1)  Shields et al.  Recent life stress exposure is associated with poorer long-term memory, working memory, and self-reported memory.  Stress, 2017 ePub.

2)  Johansson et al. Midlife psychological stress and risk of dementia: a 35-year longitudinal population study.  Brain, 2010;133:2217–2224.

3) Kiecolt-Glaser  et al.  Chronic stress and age-related increases in the proinflammatory cytokine IL-6. PNAS, 2003;100(15):9090-9095.