Researchers say that having high levels of a key steroid hormone all day can be a sign of being abused.
They found links between physical violence against women by male partners and a disruption of cortisol levels.
Women in abusive relationships had high levels through the day, spiking in the late afternoon.
The key steroid hormone opens the door potentially to a variety of negative health effects.
The University of Oregon study looked at daily fluctuations of cortisol levels in men and women.
Cortisol was drawn from saliva samples of 122 couples during on-site assessments and four times a day - upon waking up, 30 minutes later, in mid to late afternoon and at bedtime — over four consecutive days.
Cortisol levels typically rise as people wake up, peak shortly thereafter and then decline rapidly.
Researchers compared the cortisol levels with the frequency of interpersonal violence as reported by both partners in the relationships.
In the journal Psychoneuroendocrinology, the researchers said they found a disruption from normal diurnal (daily) cortisol rhythms only in women with a slower decline through the afternoons and higher-than-normal levels late in the day.
Researchers for years have suspected that the hypothalamic-pituitary-adrenal axis (HPA) regulatory system, which controls cortisol production in response to stress, is adversely influenced by violence.
'Existing studies have focused on the women's HPA-axis activity only,' said the study's lead author Hyoun K. Kim, a scientist at the Oregon Social Learning Center and courtesy researcher in the UO Department of Psychology.
'We indeed found that women's, but not men's, victimization was associated with multiple indicators of diurnal cortisol levels.
'It has been argued that interpersonal violence is more detrimental for women than for men, and our study suggests that it might indeed be due to disruptions in HPA-axis activity.'
Men in the study were recruited in 1983, when they were 9 to 10 years old, for the Oregon Social Learning Center's longitudinal Oregon Youth Study.
They were drawn from mostly lower socioeconomic status families living in neighborhoods with higher-than-average juvenile delinquency.
Their romantic partners were incorporated in a separate couples' study when the men reached 17 to 18 years of age.
Deborah M. Capaldi, a research scientist at the Oregon Social Learning Center is the principal investigator of the study.
The study's duration and large community-based sample size - not just data from women seeking help at shelters as in similar studies - make for robust findings, said Josh Snodgrass, a biological anthropologist at the university.
He currently is studying the relationships of various biomarkers, including cortisol, to health in populations around the world.
'We think we captured a good window on the subjects' everyday rhythms,' said Snodgrass, who was invited by the non-profit center to coordinate cortisol sampling and analysis.
'There are fluctuations, such as may occur on a very bad day, but it's minor and on the margins; they are easy to weed out when you have four days. It's a high-quality sample.
'We think it's the environmental and behavioral pieces that are influencing the cortisol rhythms.
The findings, the six co-authors said, show a correlation between violence and cortisol levels in women.
