COLUMBUS, Ohio, April 8 (UPI) -- Persistent fatigue that plagues many breast cancer survivors even 10 years after treatment may be caused by the autonomic nervous, U.S. researchers say.
Christopher Fagundes, a postdoctoral fellow at Ohio State University's Institute of Behavioral Medicine Research, and Janice Kiecolt-Glaser, a professor of psychiatry, used data from a larger ongoing study testing whether yoga can combat continuing fatigue in breast cancer patients.
The autonomic nervous system has two main parts -- the sympathetic, responsible for the fight-or-flight response, and the parasympathetic, the resting phase, best recognized by the sleepiness that may follow eating a big meal.
The sympathetic system is an energy hog, the parasympathetic conserves energy, and in healthy people they remain in balance.
"Sick people with inflammation become tired and lethargic, which makes sense since their bodies are using energy to fight off infections," the reseaechers say in a statement. "You can imagine that a long-term, systemic inflammation, year-in and year-out, might produce this fatigue."
The study involved 109 women -- half with fatigue and half without -- who were told to give a speech and then do a math problem. Blood tests were given. The stress hormone norepinephrine levels rose as expected from the baseline in both groups after the stressful exercise, but the researchers were surprised to see 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 says.
The findings are published in the journal Psychoneuroendocrinology.