An avalanche of chronic stress — driven by concerns ranging from parenting to discrimination —disproportionately affects poor mothers and fathers, according to the first results from a comprehensive multi-state study.

"Those who are poor have much higher stress than those who are not. In fact, being poor was associated with more of almost every kind of stress," said Chris Dunkel Schetter , a professor of psychology in UCLA's College of Letters and Science and the study's lead author.

The report found that although people with higher incomes have lower levels of stress overall, stress levels aren't reduced as much for higher-income African-Americans as they are for higher-income whites. Researchers also learned that Latinos — especially recent immigrants — tend to have lower levels of stress than other groups.

The research, funded by the National Institutes of Health's Eunice Kennedy Shriver National Institute of Child Health and Human Development, is based on extensive interviews with 2,448 mothers who had given birth within the previous month, and 1,383 partners or fathers. It was conducted in Los Angeles; Washington, D.C.; Baltimore; Lake County, Illinois; and eastern North Carolina. The study's first results were published this month in the journal Perspectives on Psychological Science.

Families were studied one month after the birth of a child, and again after another six, 12 and 18 months; some families also were interviewed after 24 months. The mothers are African-American, Latino or Hispanic, and white non-Hispanic, and a majority have household incomes near or below the federal poverty level, which in 2013 was $23,550 for a family of four.

"The vast majority of the mothers had very high levels of chronic stress while they were taking care of a new infant and, in some cases, other children as well," said Dunkel Schetter, co-principal investigator of the Los Angeles site. The results revealed high stress levels for fathers, too.

"The abundance of stress for poor parents is clear, potent and potentially toxic for them and their children," Dunkel Schetter said. "Both mothers and fathers who were poor and members of an ethnic or racial minority group reported higher financial stress and more stress from major life events like death and divorce than those who were either just poor or just part of a minority group."

The researchers measured many forms of stress that had never before been assessed together in a single study, including stress triggered by concerns about finances, parenting, partner relationships, family and neighborhood, interpersonal violence, major life events such as the death of a family member, and racism and discrimination. To gauge the biological effects of psychosocial stress, they measured cardiovascular, immune and neuroendocrine factors — including blood pressure, body mass index and salivary cortisol — which, together, offer insight into how people's body systems age in response to life events and conditions.

The researchers are part of the Community Child Health Network, a collaboration of health scientists and community partners formed by the NICHD in 2003 to investigate disparities in maternal and child health among poor and ethnic-minority families. Nationally, African-American women and poor women, for example, both are at higher risks for pre-term births, low–birth-weight infants and infant mortality than white women, even when differences in income and education are controlled.

"The consequences for families and children are quite serious," said Tonse Raju, an NICHD medical officer and co-author of the study. "Trying to learn the reasons for these disparities is a major goal of the CCHN research project."

Among the CCHN's goals are understanding the mechanisms underlying health disparities and using those findings to develop community health interventions in the five high-risk communities where the study took place.

Dunkel Schetter said the study did not support a few of the researchers' original assumptions, including their hypotheses that African-American and Hispanic parents would have higher levels of most kinds of stress, and that stress would be a major reason for the racial and ethnic disparities in health.

"It wasn't that clear cut," she said. "There were forms of stress that were higher in whites than in African-Americans and Hispanics, there were forms of stress that were quite low in the African-Americans even when they were poor, and there were forms of stress that varied in Latinos, depending on whether they were U.S.- or foreign-born."

Among the other noteworthy findings:

White women had more stress related to their pregnancies than African-American and Hispanic women.

A mother who wasn't living with the father of her baby was likely to have higher stress levels than one who lived with the baby's father.

African-American fathers were exposed to everyday incidents of racism and discrimination — a highly stressful experience — much more frequently than any other group.

Low-income African-Americans had lower financial stress than low-income whites and Hispanics.

Low-income Latino mothers and fathers were less likely to feel that life is uncontrollable and overwhelming — and reported less stress from major life events than African-Americans and whites.

Recent immigrants from Latin American countries demonstrated less stress than Latin Americans who have lived in the U.S. for longer durations or were born in the U.S.

No single ethnic group had higher overall stress levels than the others, but each showed higher stress due to certain stressors.

"Our ideas about poverty and race are often inaccurate," said Dunkel Schetter. "It's not as simple as saying, 'If you're poor and minority, you will have a lot of stress in your life.' Racial and ethnic groups bring different attitudes, cultural and behavioral backgrounds, and resources to stressful experiences."

Peter Schafer, a senior policy associate at the New York Academy of Medicine and a co-author from the Baltimore site, said, "The fact that higher income does not confer the same protective benefit from stress for black and Hispanic women as it does for whites is potentially a key insight into why racial disparities persist. This finding needs further exploration to understand if there are additional stressors for black and Hispanic women as income rises that act to offset the benefits of higher income associated with reduced levels of stress, and how we can mitigate those factors."

In a related study funded by the NICHD, Dunkel Schetter is examining how the birth of an additional child in 200 of the study's families affected the children's development by the time they entered preschool, and the parents' stress levels and overall well-being.

The university researchers worked closely with community members and organizations including, in Los Angeles, Healthy African American Families , a nonprofit dedicated to improving health in the African-American, Latino and Korean-American communities. Dunkel Schetter said Loretta Jones, the organization's CEO, was a critical collaborator, as was Dr. Calvin Hobel, the principal investigator of the Los Angeles site.

In addition to Raju and Schafer, co-authors included Robin Gaines Lanzi of the University of Alabama at Birmingham, Elizabeth Clark-Kauffman of North Shore University Health System in Evanston, Ill., and Marianne Hillemeier of Pennsylvania State University.