The effects of stress on the body have been studied scientifically since the 1930s. There are well-known effects on the endocrine system with a cascade of hormones that gets us ready for emergency situations. Secretion of adrenalin and noradrenalin from the adrenal glands is the best-known response to stress, resulting in the “flight or fight” reaction. Another adrenal hormone, cortisol, is sometimes called “the stress hormone.” When stress is ongoing, it becomes a threat to health. A mind-body connection between stress, psychological states and health was once dismissed as vague pseudoscience, but today there is an abundance of scientific data that confirm the damage stress can cause to health.Some experts claim that stress is responsible for as much as 90% of all illnesses and diseases, including cancer and heart disease.

The way it does this is by flooding the body with cortisol, which is an anti-inflammatory hormone that also decreases white blood cells. One particular type of white blood cells is consistently affected by stress. It is called the “Natural Killer” cell, or NK cell, and its job is to destroy abnormal cells, whether they are simply normal aged cells, virus-infected or cancer cells. Lowering NK cell activity is one way that high cortisol levels accelerate tumor development and growth, and increase the rate of infection and tissue damage. NK cells are large lymphocytes that, like cytotoxic T cells, are filled with granules. They selectively target tumor cells and other abnormal cells and a wide variety of infectious microbes. Unlike cytotoxic T cells, they don’t need to recognize a specific “antigen” before they attack and destroy a target cell. Unlike macrophage cells, they do not engulf and ingest target cells, but attach to them and inject chemicals that erode the membranes of the target cells until they burst. In many chronic and degenerative diseases, the level of NK cell function proves to be an important indicator of disease progression and patient prognosis. The effect of stress on NK cells is not necessarily to decrease their number, but to weaken their activity. Under stress they become relatively inert and because abnormal cells are not destroyed or eliminated, they can accumulate in the system.

Several studies have shown that reduced NK cell activity correlates strongly with the intensity and duration of the lingering mental and physical effects of PTSD. In some cases it is the only immune system parameter that can definitely be correlated with the psychological damage associated with PTSD. Even more important is the fact that PTSD can have a long-term impact on health since it is known to suppress immunity for long periods of time. Subjects with a history of PTSD have shown significantly lower immune competence even years after the initial trauma. This implies that even buried trauma could potentially be a cause or cofactor of cancer or other catastrophic illness.

A variety of “stressors” can suppress NK cell function: physical injury caused by accidents, surgery and medical treatments, nutritional deficiencies, emotional trauma, grief, hormone imbalances and others. Research on victims of disasters such as hurricanes and earthquakes show lower activity of NK cells. NK cell activity is affected by negative psychological states such as depression, anxiety and fatigue, even if lymphocyte counts and the CD4/CD8 ratio do not change. Even self-consciousness and self-criticism have also been shown to decrease NK cell activity.

The sympathetic nervous system, driven by adrenalin and noradrenalin, is an important mechanism proposed to explain the relationship between stress and NK cell activity. A neuropeptide called substance Y activates the sympathetic nervous system and significantly suppresses NK cell activity. Noradrenalin has also been shown to inhibit NK cell activity as well as b-adrenergic activation, where adrenalin activates the cardiovascular system and often associated with stress-induced changes, also appears to have an immediate and significant negative impact on the ability of NK cells to function normally.

NK cell activity can also be influenced in a positive way by a variety of factors. Music therapy and massage have both been found to increase NK cell activity. The benefits of daily massage were found even in immune-compromised AIDS patients. A study in Korea showed that emitted qi from a qigong practitioner directed at cultured tumor cells significantly increased NK cell activity in the treated group alone. Qi projection from 3 to 5 minutes in 30 second sets was optimum for increasing the NK cell activity.

Lifestyle practices also support and increase NK cell activity. Research study participants who had a healthy lifestyle with a healthy diet including a daily breakfast, adequate sleep, low stress, minimal or no tobacco and alcohol consumption had significantly higher NK cell activity.

Another way to increase immunity from enhanced NK cell activity is the use of nutritional supplements. Use of antioxidants such as NAC (n-acetyl cysteine), vitamin E and vitamin C were found to improve NK cell activity. Biological response modifiers like BioBran (RBAC) have been actively researched for their effects on immunity and physiology. BioBran increases NK cell activity and there are indications that it can even prevent excessively high levels of stress hormones like cortisol. This is important today in an era when people are living longer. Protecting and supporting immune system activity is increasingly important today to sustain longevity in people with aging immune systems.