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Since the 1950s stress has directly been linked to coronary heart disease. In one study chronic stress at work or at home was attributed to a 30% increase of death during a 9-year study. Depression has also been linked as a result to stress. But it is also noted that both heart disease and depression can cause stress.

The stress-illness connection has been considered to be cortisol. When danger is perceived a chain reaction of signals releases various hormones–most notably epinephrine (adrenaline), norepinephrine, and cortisol–from the adrenal glands above each kidney. These hormones boost the heart rate, increase respiration, and increase the availability of glucose in the blood producing the “fight or flight” reaction.

Normally, cortisol levels return to normal after 40-60 minutes, but during that time various processes either shut or slow down including: digestion, reproduction, physical growth, and some aspects of the immune system.

Although we often think of stressors as big things like abuse, illness, divorce, grieving, or getting fired. Now research shows that little things can add up to negatively impact on our health like–traffic, workplace politics, noisy neighbors, a long line at the supermarket or bank.

With prolonged stress cortisol inhibits the growth of new neurons, and can cause increased growth of the amygdala–the portion of the brain that controls fear and other emotional responses. Stress hormones also inhibit neuron growth in parts of the hippocampus–an essential area of the brain in forming new memories. The result is that the brain’s ability to put emotional memories in context is impaired. These brain changes are thought to be by some researchers at the heart of the stress — depression link as well as post-traumatic stress disorder (PTSD).

Besides heart disease, PTSD, and depression, chronic stress has been linked to ailments as diverse as intestinal problems, gum disease, erectile dysfunction, adult-onset diabetes, growth problems and even cancer. Chronic rises in stress hormones have been shown to accelerate the growth of precancerous cells and tumors; they also lower the body’s resistance to HIV and cancer-causing viruses like human papilloma virus (precursor to cervical cancer in women).

Stress is known to actually enhance one important immune response–inflammation. Ordinarily, inflammation is how a healthy body deals with damaged tissue. The infected or injured cells produce cytokines, which is a chemical that attracts immune cells to the site to help repair it. Cytokines also travel to the brain and are responsible for initiating sickness behavior. Overactive cytokine production has been found to put individuals at greater risk for a variety of aging-related illnesses.

Cytokine is has also been implicated in the link between stress and depression. People suffering from clinical depression have shown 40-50% higher concentrations of certain inflammatory cytokines. And about 50% of cancer patients whose immune responses are artificially boosted through the administration of cytokines show depressive symptoms.

Sleep may be part of this puzzle too, as disturbed sleep, which often goes with anxiety and depression, increases levels of proinflammatory cytokines in the body.

Stress is not inevitable. Even if you are a determined workaholic glued to your cell phone or a fearful and angry urban neurotic, stress-reduction methods are readily available to cope with stress in the short term and even alter perceptions of stressors in the long term.

More information about stress research currently being done in psychology, medicine, neuroscience, and genetics can be found in the December 2007 issue of the Observer. A monthly magazine of the Association for Psychological Science.