Stress has a significant effect on the immune system. It raises catecholamine and CD8 levels, which suppresses the immune system. This suppression raises the risk of viral infection. It also leads to increase of plasma catecholamines enhancing platelet aggregation, lowering cardiac threshold, inducing narrowing of the blood vessels and suppressing insulin secretion. All of these combined can lead to a high risk of heart attack.

Stress leads to the release of histamines that trigger severe bronco-constriction in asthmatics. Stress increases risk for diabetes mellitus, especially in overweight individuals, since psychological stress alters insulin needs. Psychological stress alters the acid concentration in the stomach, which can lead to peptic ulcers.

Chronic stress can also lead to plaque buildup in the arteries, especially if combined with a high-fat diet. This buildup is called atherosclerosis, and is often responsible for angina.

These diseases are by no means the only ones connected with stress, although they are the most common. Interactions between diet and stress lead to a condition that promotes endocrine imbalances that alter body fat distributions, as well as increase atherosclerosis, plaque buildup in the arteries.

Stress induces cell division among CD8 cells, thereby increasing the number of CD8 cells and suppressing immune function. Both high reactors and low reactors are affected by stress in different ways that also affects their immune system adversely.