BERKELEY, Calif. -- Even among Americans who are comfortably in the middle class, relatively modest differences in income can have a significant impact on health, a study here suggested.
BERKELEY, Calif., Aug. 17 -- On balance, richer is healthier for Americans 55 and older.
Not only that, a little bit richer can translate into a little bit healthier. And a lot richer can mean a lot healthier. It's a dose response.
So it seems on the basis of a report in the Aug. 17 issue of the New England Journal of Medicine which found that even among Americans 55 and older who are comfortably in the middle class, relatively modest differences in income can have a significant impact on the risk of functional disability.
For example, a 55-year-old man making about ,500 per year is 44% more likely to have a functional disability than his neighbor making ,800 a year, said Meredith Minkler, Dr.P.H., of the University of California here, and colleagues. This they equated with health.
If the man's income dropped to ,000 per year, his disability risk would rise to more than double that of the ,800 earner, Dr. Minkler and colleagues said.
The results suggested that the much-studied socioeconomic health disparity in the United States is not so much a chasm separating the richest and poorest but a gradient of risk affecting everyone in between, they said.
The researchers examined data from 335,000 respondents to the Census 2000 American Community Survey. Respondents were men and women ages 55 and older. The investigators analyzed the risk for functional disability-an indicator of overall health-as a function of income.
They found that compared with men making 700% of the 2000 U.S. poverty threshold, those making less were at steadily increasing risk for functional disability as their income dropped.
In the logistic-regression analyses of functional limitation, each age-sex group under the age of 85 years showed an overall downward gradient, showing that the odds of having a functional limitation decreased with distance above the poverty line.
With increasing income, the odds of reporting functional limitation declined but were still significantly higher than those of the wealthiest respondents. For respondents under the age of 85, even those at 600% to 699%t of the poverty line had significantly elevated odds ratios, as compared with those at 70%0 and higher in five of the six age-sex groups.
That risk ranged from 44% (odds ratio=1.44; 95% confidence interval=1.25 to 1.50) for men at 600% of the poverty threshold to 622% (OR=6.22; 95% CI=5.70 to 6.81) for those at or below the poverty line.
The study found a nearly identical gradient of risk for women.
The risk gradient flattened out, however, for men and women 85 or older. This finding "may reflect the fact that poorer people die younger, on average, than wealthier ones," the investigators speculated. "Selective survival of hardier poor people who are 85 years of age or older could lead to their having levels of disability similar to those of wealthier people of the same age."
The risk gradient was not explained by socioeconomic differences in access to health care, smoking, or alcohol abuse, the investigators said. Nor was race or ethnicity a significant factor, they added.
"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," Dr. Minkler and colleagues said.
"For instance, wealthier adults with problems walking can afford to renovate their homes to make them more accessible to wheelchairs," they said. "This could include widening doorways and installing ramps in the home's front entrance."
The study "suggests the importance of paying greater attention to the 'ignored determinant' of health-social class, which is strongly related to functional health across the full range of family income until very late in life," the authors concluded.
They added, "With almost 85% of Americans who are 55 years of age or older living at an income level under 700% of the poverty line, this is not simply an issue of very poor people having a disadvantage in health outcomes Rather, higher risk is demonstrated across a very large proportion of the older population, as compared with the most advantaged."
They examined "functional limitation because it is more closely related to intrinsic problems caused directly by disease, disuse, and aging, than are more basic activities of daily living."
"Older adults who can afford to modify their bathrooms and make them more accessible, for example, will reduce their bathing disability without substantially altering their functional limitation," they wrote.
Their sample included 149,000 men and 186,675 women who were at least 55 years old. "These included 32,680 men and 48,111 women who reported having a functional limitation (a long-lasting condition that substantially limited one or more basic physical activities, such as climbing stairs or lifting)."
The authors noted that Medicare has helped to decrease the disparities in race and income in the access to and use of preventive and therapeutic care among older Americans, but marked differences remain. "Lower-income beneficiaries, for example, are less likely to be able to afford Medicare's deductibles, coinsurance, and uncovered services, and hence they may not elect to have some procedures that could improve their functional status," the investigators wrote.
As a limitation to the study, the investigators cited access only to cross-sectional data, making it impossible to know whether lower income preceded or followed the onset of functional limitation-and "reverse causality is an important consideration."
But, they added, the majority of disability in old age is acquired later in life.
"The measure of socioeconomic status that is least vulnerable to reverse causality is education because completion of schooling usually predates, by several decades, the onset of disability," they wrote. "Our finding of a similar downward gradient between educational level and functional limitation, and other research demonstrating that social class in middle age predicts health status in old age, provide support for the hypothesis that, in many cases, lower socioeconomic status precedes the onset of disability."
They cited a further limitation of the study involving its sole reliance on income data "rather than on more complex measures of household wealth, which are particularly important in research with older respondents."