DURHAM, N.C. --Stress hormone levels in working mothers rise each morning and stay high until bedtime, putting them at higher risk than other working women for health problems such as heart attack, according to a study by Duke University Medical Center researchers. The number of children at home made no difference in stress levels -- stress hormone levels were as high with one child as with several.
"The good news would be that working mothers' stress levels don't go up with the number of children in the home," said Dr. Redford Williams, chief of behavioral medicine at Duke and primary investigator for the study published in the July 23 issue of Psychosomatic Medicine. "The bad news is it only takes one to boost that stress level."
Linda Luecken, lead author of the study, cautioned that since the study did not include stay- at-home mothers, the researchers can't compare stress levels of working mothers and mothers not employed outside the home. "It is tempting to consider this as evidence that mothers should not work outside the home, but until we compare stress levels of the two groups of mothers, we cannot draw any such conclusions," she said.
The research, funded by the National Heart, Lung and Blood Institute, studied 109 women working in clerical and customer service positions. The level of hormones associated with stress that are excreted in urine was measured over a two-day period. Study participants collected urine samples in three time periods, during the workday, in the evening after work and from bedtime through waking. Urine samples were later measured for hormones related to stress, including cortisol, norepinephrine and epinephrine.
The women also completed a series of questionnaires, including demographic information, evaluation of stress at home and at work and measures of social support. Researchers correlated hormone excretion levels with other factors such as whether the women were single or married, whether they had children at home and the number of children in the household.
Regardless of marital status, women with children living at home excreted higher levels of the stress hormone cortisol throughout a 24-hour period than did working women without children, the researchers reported. Mothers with one child at home had stress hormone levels as high as working mothers with more than one child. While the level of cortisol peaked during working hours for all women, the levels were consistently higher throughout the day for working mothers.
All participants showed a significant increase in levels of epinephrine and norepinephrine, known as catecholamines, during the workday and there was little, if any, change from workday to evening levels. In contrast, other studies have shown men experience a drop in catecholamines when they come home from work.
Catecholamines are associated with "effort" or activity, Williams said, while cortisol has been shown to relate to "distress" and a lack of personal control. Chronic elevations of cortisol in working mothers could lead to health problems, he said, by suppressing the immune system and also heightening the impact of the catecholamines.
"We believe the increased stress levels seen in the employed mothers is related to increased strain at home, rather than work strain, but that the increased strain exerts its physiological effects over the entire day," Luecken said.
Williams said job strain was about the same in all the women, but the working mothers reported significantly higher levels of home strain than women without children, and that again, the level of strain was independent of marital status. The working mothers reported both higher demand on them in the home and lower control of the situation.
In other studies, increasing social support reduced stress levels, but the Duke researchers found social support did not buffer the effect of having a child. Instead, Williams and the other Duke researchers said quality of work and family experiences may be key factors in the women's stress levels.
"The level of satisfaction at work and home may be what makes a difference," Williams said. "Maybe the only way to reduce the burden on these working mothers is to share it, to more equally divide home responsibility."
Besides Williams and Luecken, Edward Suarez, Cynthia Kuhn, John Barefoot, James Blumenthal and Ilene Siegler worked on the research project.