Stress is a normal reaction to environment events and is a desired response in a dangerous situation. This reaction is referred to as “fight or flight” response or stress response. Stress response is manifested by some evident physiological signs such as dilated pupils, increased sweat secretion, accelerated heart rate, and faster breathing.  Besides the observable physical signs of stress response, especially to acute stress, stress hormones are released and regulated by hypothalamic-pituitary-adrenal (HPA) axis . Stress hormones activate body’s natural defense system against stress – the relaxation response which return body’s physiological state to the normal level. Stress response within normal range is actually beneficial to the health and it is how human can adapt and respond to environmental events or threats. Moderate stress sharpens sensory experience, enhance concentration and memory and quicken reaction time. However, excess stress or chronic stress can result in serious health problems because the “relaxation response” stop functioning under persistent stress stimulation. It is found that aging is a factor that impair the natural relaxation response capacity, making elders more vulnerable to adverse health effect of chronic stress. The psychological manifestation of stress response is often associated anxiety and depression – The terms stress and anxiety are often used interchangeably and they share similar and overlap symptoms.

Stress response is mediated by the stress hormones produced by adrenal. They are important regulator of the stress response. Cortisol is the primary stress hormone, together with adrenaline, norepinephrine.   Adrenaline is known to accelerate heart rate, inhibit digestion, constrict blood vessels. Norepinephrine also accelerates the heart rate. It also affect the part of brain that is responsible for attention or focus.

Chronic stress is associated with persistent cortisol level in the blood and brain which exerts adverse effect on the health. Cortisol – the primary stress hormone – increases blood pressure and regulate blood sugar (glucose) metabolism and insulin production as well as many other functions. Cortisol is believed to weaken the immune system and lowers growth hormone which contribute to the aging process. Small increases of cortisol have some positive effects. The long-term activation of the stress-response system — and the subsequent overexposure to cortisol and other stress hormones — can disrupt almost all body’s processes, causing a variety of symptoms related to the cognition/memory function, psychological disturbances, physical or physiological symptoms (fatigue, insomnia, weight gain and etc.). Health problems associated with chronic stress include: digestive problems, cardiovascular problems, impaired cognitive performance , suppressed thyroid function, hyperglycemia, decreased bone density, decrease in muscle tissue, weakened immunity and inflammatory responses, and other health consequences

How does chronic stress accelerate the normal aging process? What are the molecular and cellular mechanisms? Academic studies have suggested three mechanisms via which stress and stress hormone can speed up the aging process.

• increased oxidative stress and free radical damage (in the brain):

Chronic stress is associated with increased ROS (reactive oxygen species) production and free radical damage (in the brain).  Cortisol seems to be able to interfere with the neurotransmitters’ activities. In addition, Cortisol may divert energy (glucose) from brain to the muscle. Cognition impairments are often associated with severe chronic stress and/or anxiety. (see post “how stress affect memory”).

• accelerate aging of immune system:

Cortisol suppresses and weakens the immune system in general. Social and psychological stress is now known to affect immunity through specific autonomic and neuroendocrine pathways. Evidence has been accruing that chronic stress exacerbates age-related immune decrements, and sometimes accelerates the effects of aging to produce lasting and deleterious effects on immune functioning. see article for aging of immune system.

• shortened telomere length (a marker of biological aging):

Telomere shortening is the most extensively observed phenomenon associated with chronic stress as well as depression and anxiety as far as its effect on aging is concerned. Researchers found that chronically elevated levels of cortisol damages the telomeres and perhaps genes in the body.” For how telomere shortening is associated with aging and why telomere shortening is a marker of aging, see article “Telomere Shortening and replicative senescence” and post “Telomere Shortening – The Secret to Aging?” and “Is telomere length a biomarker of stress and aging?“.