Noradrenaline, adrenaline, cortisol and other hormones help mobilize glucose and fats from the body stores, so increasing blood glucose, cholesterol and triglyceride (fat) levels. A high level of circulating blood cholesterol is considered a coronary heart disease risk factor because cholesterol is a major component of plaque. Damage to the inner lining of the blood vessel increases susceptibility to the plaque-forming process by allowing cholesterol to penetrate into the blood vessel wall. There is some evidence to suggest that high circulating levels of noradrenaline and adrenaline can cause this damage.
It is popularly believed that cholesterol from food is solely responsible for elevating blood cholesterol levels but it is not always realized that far more is produced during periods of stress than can be obtained from the diet.
A number of research studies have shown how blood cholesterol levels rise during periods of stress. In one such experiment blood cholesterol was measured in two groups of accountants throughout a period of about six months. During this time the accountants were asked to keep a record of their lifestyle (diet, exercise and so on) and also how much pressure and stress they experienced. Accountants were chosen for the experiment because they work to deadlines. In fact, one group were tax accountants who had one deadline to meet in April whilst the others were corporate accountants who had deadlines in January and April. Figure 12 shows that, for both groups, there is a peak in blood cholesterol levels coinciding with the deadlines; one for the tax accountants and two for the corporate accountants. Almost all the accountants reported feeling pressured around the time of the deadline but there was no reported significant change in diet or exercise.
When the level of fat in the blood increases, the blood becomes thicker and more viscous. This also occurs when more red cells are pumped into the circulation from the spleen during the stress response. The heart must work harder to circulate thicker blood, therefore myocardial oxygen consumption increases.
Another problem with thicker blood is that red blood cells can form a â€˜sludgeâ€™ which may block small blood vessels. Sludging in the very small blood vessels of the heart and brain can lead to a heart attack or stroke respectively.
Thus a good case can be made for the involvement of the stress response in circulatory diseases: coronary heart disease, sudden cardiac death, hypertension and strokes. These diseases may result from the interaction between stress and other factors such as diet, smoking and Type A Behaviour.