The Impacts of Stress

[Dr. Adams]

"Reactions to stress affect brain aging via hormonal effects, stress means 'allostatic load,' or the cumulative effect of stress and lifestyle — that is, what we eat, drink, if we smoke, how well we sleep, whether we are physically active — these are determined in part by our life experiences, which include stress and being anxious and worried, under much tension in a job or at home, etc. Effects that we know about include impairment of memory, shrinkage of the hippocampus, impaired glucose utilization. Based on animal models and some human data, the adrenal stress hormone cortisol appears to play an important role in mediating the effects of stress on the brain. The hippocampus, a vital brain region for episodic, spatial, and contextual memory, has many cortisol receptors, which makes it especially vulnerable to stress hormones. Although acute stress seems to enhance immune function and improve memory, chronic stress has the opposite effect and may even lead to disorders that become more prevalent with aging, such as depression, diabetes, and cognitive impairment. Diabetes and obesity are risk factors for cognitive decline and for Alzheimer's disease, as well as for depression, and that comorbidity of diabetes and dementia may first be manifest as geriatric depression. Depressive illness over a long time [years] leads to shrinkage of the hippocampus. The overall lack of physical activity and the epidemic of obesity and diabetes are matters of concern, then, for brain health. The brain may be the most sensitive indicator of chronic stress. A person who has been overexposed to cortisol, due to chronic treatment with high doses of prednisone or excessive duration of experiencing chronic stress, will likely have an atrophied hippocampus. Functionally, this person will likely show deficits in certain types of memory. Disrupted circadian rhythms may also reflect brain aging. Although the brain "clock" efficiently regulates diurnal rhythms of hormonal levels in youth, the aged brain is less efficient in regulating hormonal cycles. The low levels of anabolic hormones or dysregulated levels of cortisol that we often see in the blood of the elderly is likely a reflection of this aged clock losing its sense of timing, in that it now sends the hormone-releasing signals to the body in a more dysregulated way. Aging alone alters most hormonal signals from the brain, leading to lower levels of anabolic hormones, [but] stress can also alter these brain signals, thus speeding up the age-related decline in anabolic hormones. In this way, chronic stress may alter the rate of hormonal aging. With aging, decreased levels of anabolic hormones lead to other age-related changes, such as decreased bone mass, and shifting body composition toward greater fat mass and lower muscle mass. Older people are exposed to more chronic stressors, but they do not necessarily experience greater daily stress. Adaptive coping strategies successfully used by the elderly include finding meaning in life events, strengthening meaningful social ties, and spiritual or religious beliefs. Even in younger individuals, these strategies tend to be linked to more adaptive profiles of hypothalamic-pituiutary axis function (either diurnal rhythm or reactivity) after facing a major stressor."