Stress affects the body in many different ways. While the short term physical responses to stress are well known, some longer term effects of stress are less well understood. However, thanks to ongoing research a lot more is known about stress than was the case even a few decades ago.

Stress causes a set of physical responses collectively known as the "fight or flight" response. The hormone adrenaline is released into our bodies in order to prepare us to escape from danger or fight off the threat. Our heart rate increases, respiration becomes more rapid, muscles tense and our senses become sharper. This is a response possessed by most animals.

What happens in biological terms is that when we sense a threat, an alarm is set off in the brain by the hypothalamus. It does not distinguish between types of threat, although it will vary the strength of the reaction depending on the degree of threat and whether the threat is immediate. This means that it reacts not only to a physical danger (muggers in the street) but also to a competitive danger (second place race runner challenging our lead) or an emotional, psychological or financial danger (boss threatens us with dismissal if report is not on his desk in 15 minutes).

The sympathetic nervous system and the endocrine glands receive a signal from the brain and then fill the body with the stress hormones. These hormones include adrenaline, cortisol and norepinephrine. These are our bodies' equivalent of putting "all hands on deck".

The increase in heart rate allows more blood to reach our large muscle groups so that we are prepared to run faster or fight harder. In order to reduce bleeding in case of injury, the blood vessels close to the surface of the skin constrict and our blood sugar levels spike to give us more energy and a faster reaction time.

During this time, our reproductive and digestive systems slow down, as does the flow of growth hormones and the immune system.

When we are confronting a real physical danger, this response is very useful. It improves our chances of surviving the situation.

However, the vast majority of situations which provoke this response in modern man have nothing to do with physical threats, but rather workplace deadlines and the like. As tempting as it may be to either run away or punch your boss, it's generally not appropriate.

So we do not use the adrenaline response that has been activated, and because it is not used, it does not go away as quickly as it might. Often, before we have completely recovered from one stress reaction, another problem presents itself and we have a new adrenaline boost.

The result is that many of us spend the greater part of each day in a state of stress, with physical tension, an overworked heart and unnecessary amounts of adrenaline constantly in our system. The long term effects can be varied and serious. They can result from the overworked circulatory system or the unresponsive digestive, reproductive and immune systems, and can cause anything from migraine to a heart attack, depending on our susceptibilities.

The effects of stress on the body places undue stress on our heart, which keeps us from staying in good health; it's no wonder why we get ill.