Stress is a pervasive condition that affects our mental and physical functioning. The term covers both situations that we may call “stressful” such as being told we have cancer or Alzheimer’s disease, caregiving for someone with dementia, or having to give a speech or our reaction to the stressful event such as racing heart, dry mouth, or worry. Stress can be “negative,” as in being sued, having a car accident, or getting divorced, or “positive,” as in taking a vacation, getting married, or winning the lottery.
Stressors vary in terms of duration, intensity, novelty, and type. The ranges of stressors includes threat of death, threat of bodily injury, illness, grief, divorce, grief, moving, night shift work, commuting, and noise.
The formal study of stress started with the seminal book The Stress of Life by Hans Selye that was published about 70 years ago. He is credited as the first to describe the impact of mental events on body tissues. There are two major biological systems that are engaged by stressors. The sympatho-adreno-medullary axis that releases adrenaline and the Hypothalamic-Pituitary-Axis that releases CRF, ACTH, and cortisol. These systems have a profound and pervasive effect on the body during engagement of the “flight-or-fight response.”
People vary greatly in their ability to handle stress. Some are more resilient than others depending on such factors as cognitive abilities, physical makeup, mental health, social support, and proneness to substance abuse. More contemporary research on stress addresses possible neurotoxic effects. We may ask does stress does contribute to or cause dementia? Greenberg, Tanev, Marin, and Pitman provide a recent review of this topic (Stress, PTSD, and dementia, Alzheimer’s and Dementia, 2014, 10, S155-S165 http://www.ncbi.nlm.nih.gov/pubmed/24924667).
Greenberg et al. reviewed 8 studies that focused on the correlation between life stress and cognitive impairment. Two longitudinal studies focused on a cohort of Catholic nuns – the longest being 5 years. The results indicated that those high in neuroticism (assume higher stress) showed greater cognitive decline than those low in neuroticism. There was no association with Alzheimer’s disease. Another study measured the correlation between stressful life events and cognitive decline in participants with and without Mild Cognitive Impairment. High stress in normals was not associated with cognitive decline but high stress was associated with faster decline in those with Mild Cognitive Impairment.
A longitudinal (35 years) Swedish study of women found that those with the most stress had great white matter disease on MRIs as well as a higher rate of Alzheimer’s disease whereas a second Swedish study showed that high job strain with low social support was associated with higher rates of vascular dementia.. A Chinese longitudinal study (5 years) found an association between death of a spouse or financial crises but not death of an offspring, serious illness, accident, or law suit with cognitive impairment. Finally, a British study found an association between perceived stress, low education and lowered MMSE scores.
In conclusion, it appears that stress does not cause dementia or more specifically Alzheimer’s disease. Stress may contribute to cognitive impairment in some but dementia. Even for those with Post Traumatic Stress Disorder (those experiencing profound stressors), most (90%) did not develop dementia. It appears that chronic stress is neither necessary nor sufficient to cause dementia.