Stress encompasses the strains experienced by living organisms in their struggles to adapt and cope with changing environments.

When danger is perceived, a chain reaction of signals releases hormones like epinephrine (“adrenaline”), norepinephrine and cortisol from the adrenal glands. These hormones kick up the heart rate, increase respiration, and up the glucose levels in the blood – enabling the “fight or flight” reaction.

As these responses take a lot of energy, cortisol tells other physical processes – including digestion, reproduction, physical growth and some aspects of the immune system – to shut or slow down.

When the threat passes, the body’s stress thermostat adjusts accordingly. Cortisol levels return to normal and the body resumes its usual functions. But problems occur when stresses don’t let up, or when, for various reasons, the brain continually perceives stress even if it isn’t really there.

This causes prolonged exposure to cortisol, which 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. It also affects the hippocampus, an area that helps form new memories.

Researchers now say these brain changes are at the heart of the link between stress and depression as well as posttraumatic 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 pre-cancerous cells and tumours; they also lower the body’s resistance to HIV and cancer-causing viruses.