For the innate immune system, the first immunological line of defense against cancer and pathogens, stress is just as important a factor as sleep and physical activity. We reviewed two human studies.

Study 1
In 2005, immunologists from Kanazawa Medical University in Japan published a study in the Journal of Occupational Health in which they drew blood samples from 61 female nurses aged 23-59. [J Occup Health. 2005 Sep;47(5):378-83.]

The researchers extracted CD16+CD56+ natural killer cells (NK cells) from the nurses' blood, added cancer cells, and measured how many cancer cells the NK cells could eliminate (cytotoxic NK cell activity).

At the same time, the researchers had the nurses complete the Japan Nursing Job Stressor Scale questionnaire. Based on this questionnaire, the researchers determined the quantitative workload - that is, the amount of work - the nurses had to perform. This allowed the researchers to categorize the nurses into three equal-sized groups, or tertiles, based on their workload.

Results of study 1
The higher the workload nurses reported, the lower the ability of their CD16+CD56+ NK cells to eliminate cancer cells [and pathogens]. Furthermore, high workload reduced the number of CD16+CD56+ NK cells.

The cytotoxic activity of the NK cells in the tertile with the highest workload was 37 percent lower than in the tertile with the lowest workload. The number of NK cells in the tertile with the highest workload was 30 percent lower than in the tertile with the lowest workload.

Click on the table for a larger version.

The negative immunological effect of work stress is therefore similar to that of a lack of sleep. Reducing work stress has an immunological effect roughly equivalent to that of a lifestyle with plenty of exercise.

Study 2
The Japanese study involved women. According to an Italian study from the University of G. D'Annunzio of Chieti-Pescara in 2009, men respond to work stress in a similar way. [Int Arch Occup Environ Health. 2009 May;82(6):787-94.]

The Italians took blood samples from male university employees, extracted NK cells, and measured their cytotoxic activity. They also found a link between work stress and NK cell activity.

In the figure below - click on it for a larger version - you can see, for example, that NK cells were more active in young men with permanent contracts [and therefore little work stress] than in young men with temporary contracts [and therefore relatively high stress].

More coming soon.