New study links higher income with lower disability rates
Berkeley -- Numerous studies have already established the link between extreme poverty and poor health, but a new study led by a public health researcher at the University of California, Berkeley, has found that health disparities exist even between those with higher incomes.
"What was unusual was that we found that people in the middle class were still at a disadvantage compared with those at just a slightly higher income," said Meredith Minkler, professor of health and social behavior at UC Berkeley's School of Public Health and lead author of the study, published in the Aug. 17 issue of the New England Journal of Medicine. "The fact that there's a significant difference between people at 600 and 700 percent above the poverty level was a striking finding of this study."
Household income was categorized into nine levels, from less than 100 percent of the poverty line to 700 percent and higher. In 2000, the poverty threshold for a person living alone who was 65 or older was $8,259 per year, and it was $17,761 for a four-person household. A single 65-year-old living at 600 percent of poverty would therefore earn $49,544 per year in income while someone at 700 percent of poverty would earn $57,813. A four-person household at 600 percent of poverty would take in $106,566 per year, while the comparable annual income at 700 percent is $124,327.
"We have lots of evidence that wealthier people in society are healthier and live longer than the poorest, but less settled is whether you see this gradient with respect to disability, and whether it plays out among older people," said Minkler.
The researchers found significant differences in the rates of limitations even among those in the upper income brackets. Among those who were 55-74 years old, even those at 600-699 percent of the poverty line had elevated odds of having a disability compared to those at 700 percent and higher. For example, women aged 55-64 in the 600-699 percent category had 16 percent higher odds of disability than women in the 700 percent bracket, and men aged 65-74 in the 600-699 percent group had 44 percent higher odds than men in the 700 percent group.
Co-authors of the study are Esme Fuller-Thomson, associate professor of social work at the University of Toronto, and Jack Guralnik, M.D., chief of the Laboratory of Epidemiology, Demography and Biometry Section at the National Institute on Aging.
The researchers looked at data from 335,000 respondents aged 55 and older to the Census 2000 American Community Survey. They compared poverty level status with the rate of functional limitation, defined as a long-lasting condition that substantially limited one or more basic physical activities, such as walking, reaching or lifting. They chose functional limitation as a variable over death or illness, since many chronic diseases affect functional status.
Of the respondents surveyed, 80,791 had functional limitations. Not surprisingly, the prevalence of functional limitation increased with age. Among men aged 55-64 years, 16.2 percent reported some level of functional limitation compared with 47.5 percent for those aged 85 years and over. Among women who were 55-64 years old, 17.2 percent had functional limitation compared with 57.9 percent for those 85 and over.
The researchers found the biggest differences among the younger age group, those aged 55-64. In that group, people who were living in poverty were six times more likely to report functional limitation than people in the same age group who were living at or above 700 percent of the poverty level, with very little difference between men and women.
"These findings underscore that poverty is one of the major risk factors for disability," said Fuller-Thomson.
The study authors point to a number of possible explanations for the social gradient in health. The upper class has lower rates of smoking, and may have less stress, better access to health coverage, and healthier environments, including safer neighborhoods that encourage walking and have less pollution, even when compared with those living comfortable middle class lives, according to the researchers.
"We know that Americans 55 and above today are relatively health conscious compared to prior generations, but it may be that the wealthiest Americans have the greatest edge in acting upon their motivations to stay healthy," said Minkler. "For instance, wealthier adults with problems walking can afford to renovate their homes to make them more accessible to wheelchairs. This could include widening doorways and installing ramps in the home's front entrance."
The researchers point out that while the rate of disability has been declining slowly but steadily over the past two decades, the aging of the baby boomer generation means that the sheer number of people with disabilities is going to increase.
"There are now almost 8,000 people turning 60 every day in the U.S.," said Minkler. "It's therefore important for us to understand all of the factors that affect disability rates. Social class is a badly neglected determinant of health and illness. This study highlights that socioeconomic status operates independently of such factors as race, ethnicity and health behaviors. Although researchers often control for social class, it warrants much more focused attention."
The study was funded by a grant from the Retirement Research Foundation with additional support from the National Institute on Aging, part of the National Institutes of Health.
Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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