Smoking And Depression Weakens Immune System

The combination of depression and cigarette smoking contributes to increased white blood cell count and a decline in the activity of natural killer cells (NK) that fight off tumors, the study demonstrated.

The research was conducted by Waymund Jung, MD, and Michael Irwin, MD, at the University of California, San Diego and the Veterans Affairs San Diego Healthcare System Administration Medical Center. The results of their research are reported in the June issue of Psychosomatic Medicine.

"The findings may have particular importance in view of the high rates of smoking among depressed persons reported in other research," Irwin said.

"The immune changes in depressed smokers, along with the finding that depression and smoking interact to contribute in a unique way to elevated white blood cell counts and reduced NK activity, suggest that even moderate cigarette smoking can impact the immune system adversely," said Irwin.

The scientists took blood samples to measure white blood cell counts and NK activity of 245 men in four distinct groups: 61 depressed moderate smokers, 46 depressed non-smokers, 127 non-smoker controls, and 11 moderate smoker controls.

Neither depression alone nor smoking alone was linked with decreased NK cell activity or higher white blood cell count.

In pairwise comparisons the researchers found:

* Depressed smokers had lower NK activity than depressed non-smokers.

* Control subject smokers and non-smokers had similar levels of NK activity.

* Depressed non-smokers and control subjects had similar levels of NK activity.

The immunological findings of the present study are compatible with epidemiological data that show that depressed mood and smoking contribute to the development of cancer, the scientists said.

The research was supported by grants from the National Institute of Alcohol Abuse and Alcoholism, the National Institute of Mental Health and the National Institutes of Health.