Persistent fatigue in breast cancer survivors may be caused by autonomic nervous system running in overdrive

February 29, 2016

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 researchers also gauged another measure in the study, the natural variability in heart rate which decreases as a person ages. A lessened heart rate variability (HRV) is also an indicator of activity in the parasympathetic, or "resting," system.

"People who were fatigued had weaker parasympathetic activity than those who weren't," he said.

"One of the things we know best is that exercise can enhance a person's HRV," Kiecolt-Glaser said. "Exercise is also the best documented treatment for fatigue, so this all begins to make sense.

"Fatigue isn't a symptom that should be ignored. It's a marker for other things that might be going on," she said. Higher norepinephrine levels and lower HRV have been linked to high blood pressure, myocardial infarctions, strokes and diabetes.

"When a cancer patient reports persistent fatigue following treatment, it is something that deserves attention. It may be a symptom of other things that matter."

Source: Ohio State University