A new study suggests that the persistent fatigue that plagues one out of every three breast cancer survivors may be caused by one part of the autonomic nervous system running in overdrive, while the other part fails to slow it down.
That imbalance of a natural system in the body appears linked to the tiredness and exhaustion that can burden cancer patients as much as a decade after their successful treatment.
Researchers say that the effect is so great that it may be a sign of accelerated aging in fatigued patients, causing them to seem as much as 20 years older compared with patients who aren`t fatigued.
Christopher Fagundes, a postdoctoral fellow at Ohio State University`s Institute of Behavioral Medicine Research (IBMR), and Janice Kiecolt-Glaser, a professor of psychiatry and psychology and a member of the IBMR, were looking for a new biomarker, a signal that could point to the initial cause of this fatigue.
Their target was the autonomic nervous system, that part of the body that controls unconscious activities like breathing, heartbeat, digestion.
The autonomic nervous system has two main parts – the sympathetic and the parasympathetic. The former is responsible for what has become known as the fight-or-flight response, a triggering of short-term, energized activity. The latter deals with opposite situations. It is the resting phase, best recognized by the sleepiness that may follow eating a big meal.
While the sympathetic system is an energy hog, the parasympathetic conserves energy, and the two should remain in balance in healthy individuals.
For the study, 109 women participated and were placed in one of two groups – those who reported long-term fatigue and those who didn`t. The women varied from being two months to two years after being treated for their disease.
After a short relaxation period, each woman had blood drawn to establish a baseline level for norepinephrine, a stress hormone that served as an indicator of activity by the sympathetic nervous system. Each participant had to give a five-minute speech before a two-person panel and then do a series of verbal arithmetic problems aimed at increasing stress levels. Additional blood samples were taken immediately after the stressor and then a half-hour later.
The norepinephrine levels rose as expected from the baseline in both groups after the stressful episode but the researchers were surprised to see something different. Regardless of the stressor, women who had persistent fatigue showed higher levels of norepinephrine than those who weren`t fatigued.
"They had higher sympathetic activity and lower parasympathetic activity," Fagundes said, an indication that other researchers have suggested is a signal for inflammation.
The findings have been reported in the journal Psychoneuroendocrinology.