Scientists have known for decades that poverty leads to higher rates of illness and mortality. More recent research led by UCSF faculty has shown that these effects don't end at the poverty line. In fact, health improves at each step of the social ladder.
"It is not simply the effects of income or education that are linked to better health, but also the perception that one is higher on the social hierarchy," said Nancy Adler, PhD, UCSF professor of psychiatry and lead author of the study which appears in the November issue of Health Psychology, a journal published by the American Psychological Association (APA).
The researchers found that women who placed themselves higher on the social ladder reported better physical health, took less time to fall asleep at night and had lower resting heart rates and less abdominal fat (a key indicator that these women adapt to stress better), said Adler. Perceptions of lower social standing were also associated with negative psychological factors, including greater chronic stress, pessimism and lower perceived control of life.
The researchers studied a sample of 157 healthy white women age 30-46. In addition to reporting on their income and education, the women completed a new survey that asked them to rate their own socioeconomic status (SES).
They were shown a drawing of a ladder with ten rungs and told to think of the ladder as representing where people stand in society. At the top of the ladder are people who are best off - those who have the most money, education, and best jobs. At the bottom are people who are the worst off - who have the least money, least education and worst jobs. Participants were then asked to place an "X" on the rung which best represented where they think they stood on the ladder.
The women, who had varying socio-economic backgrounds, were evaluated for psychological indicators, including negative affectivity (how much they generally tend to feel negative emotions), pessimism, perceived control over life, coping style, self-defined stress levels, and chronic stress levels.
Participants were also evaluated for sleep patterns, resting physiological response, and fat distribution. A sub-sample of 59 women took part in a laboratory stress study that examined their cortisol response to stress over a three day period.
Cortisol is a stress hormone that may play a role in the accumulation of abdominal fat, explained Adler. Abdominal fat deposit, in turn, is linked to metabolic and cardiovascular disease.
"With repeated experiences of the stress, the body has greater exposure to cortisol. Abdominal fat has a relatively greater sensitivity to cortisol than peripheral fat, so individuals with higher cortisol reactivity, high resting levels of cortisol and /or great exposure to events that evoke a stress response accumulate greater abdominal fat," she said.
Researchers analyzed the accumulation of body fat by measuring body mass index (BMI) and waist-to-hip ratios. They found that women who consistently secreted cortisol when exposed to repeated stress had the lowest ladder ratings.
"Our findings suggest that perceived low SES is linked to greater stress. Low subjective SES may either increase stress directly or make women more vulnerable to the effects of stress," said Adler. She explained that lower ladder rankings are linked to increased stress even when researchers controlled for a woman's actual socioeconomic placement (determined by education, occupation, income) and how much these women report experiencing negative emotions.
The research serves as a human analog to studies of social ordering and health among animals, explained Adler. Subordinate primates have higher cortisol, higher blood pressure, and worse health than dominant animals in stable social environments, according to previous research.
"The ladder rankings may reflect direct social comparisons of social rank that are more similar to dominance hierarchies than are traditional measures of SES that include education, occupation, income," she said.
The fact that all participants were healthy, white women who had at least a high school degree presents a limitation to the study, according to the researchers. In a second and related paper, published in the same issue of Health Psychology, researchers determined that subjective status may be a more important determinant of self-rated health for women who have higher income levels - in this case whites and Chinese Americans.
For Latina and African Americans, who had lower average incomes and education levels, household income was the most important determinant of how these women rated their health.
Co-investigators on the first study included Elissa Epel, PhD, post-doctoral fellow in the UCSF department of psychiatry; Grace Castellazzo, BSN, research nurse at Yale University; and Jeannette Ickovics, PhD, associate professor of epidemiology and public health at Yale University. The lead author on the second study was Joan Ostrove, PhD, assistant professor of psychology at Macalester College. Co-investigators included Adler, Miriam Kuppermann, PhD, MPH, UCSF assistant professor of obstetrics and gynecology; and A. Eugene Washington, MD, UCSF professor and chair of obstetrics, gynecology and reproductive sciences.
Both studies were funded in part by the John D. and Catherine T. MacArthur Foundation Research Network on SES and Health. Other funding came from the National Institute of Mental Health, the National Institute of Child Health and Human Development, the Agency for Health Care Policy and Research, the National Center for Human Genome Research, and the American Psychological Association Division of Health Psychology.
Journal
Health Psychology