Impact of Income and Income Inequality on Infant Health Outcomes in the United States

OBJECTIVES: The goal was to investigate the relationships of income and income inequality with neonatal and infant health outcomes in the United States. METHODS: The 2000–2004 state data were extracted from the Kids Count Data Center. Health indicators included proportion of preterm births (PTBs), proportion of infants with low birth weight (LBW), proportion of infants with very low birth weight (VLBW), and infant mortality rate (IMR). Income was evaluated on the basis of median family income and proportion of federal poverty levels; income inequality was measured by using the Gini coefficient. Pearson correlations evaluated associations between the proportion of children living in poverty and the health indicators. Linear regression evaluated predictive relationships between median household income, proportion of children living in poverty, and income inequality for the 4 health indicators. RESULTS: Median family income was negatively correlated with all birth outcomes (PTB, r = −0.481; LBW, r = −0.295; VLBW, r = −0.133; IMR, r = −0.432), and the Gini coefficient was positively correlated (PTB, r = 0.339; LBW, r = 0.398; VLBW, r = 0.460; IMR, r = 0.114). The Gini coefficient explained a significant proportion of the variance in rate for each outcome in linear regression models with median family income. Among children living in poverty, the role of income decreased as the degree of poverty decreased, whereas the role of income inequality increased. CONCLUSIONS: Both income and income inequality affect infant health outcomes in the United States. The health of the poorest infants was affected more by absolute wealth than relative wealth.

[1]  R. Cohen,et al.  Income inequality and mortality in metropolitan areas of the United States. , 1998, American journal of public health.

[2]  J. Nonnemaker,et al.  Income Inequality, Race, and Child Well-being: An Aggregate Analysis in the 50 United States∗ , 2004, Journal of health and social behavior.

[3]  William Pickett,et al.  Influence of individual- and area-level measures of socioeconomic status on obesity, unhealthy eating, and physical inactivity in Canadian adolescents. , 2006, The American journal of clinical nutrition.

[4]  Patricia B. Reagan,et al.  Race and ethnic differences in determinants of preterm birth in the USA: broadening the social context. , 2005, Social science & medicine.

[5]  A. Birn.  The Health of Nations: Why Inequality Is Harmful to Your Health , 2003 .

[6]  D. Colombo,et al.  Closing the gap in a generation: health equity through action on the social determinants of health. Final report of the Commission on Social Determinants of Health , 2010 .

[7]  K. Judge.  Income distribution and life expectancy: a critical appraisal , 1995, BMJ.

[8]  R. Wilkinson.  The epidemiological transition: from material scarcity to social disadvantage? , 1994, Daedalus.

[9]  T. Lobstein,et al.  Wider income gaps, wider waistbands? An ecological study of obesity and income inequality , 2005, Journal of Epidemiology and Community Health.

[10]  P. Sorlie,et al.  Income inequality and mortality: a multilevel prospective study of 521 248 individuals in 50 US states. , 2007, International journal of epidemiology.

[11]  E. Doorslaer,et al.  Income inequality and health: what does the literature tell us? , 2000, Annual review of public health.

[12]  B Kennedy,et al.  Income inequality, primary care, and health indicators. , 1999, The Journal of family practice.

[13]  R. Wilkinson,et al.  Child wellbeing and income inequality in rich societies: ecological cross sectional study , 2007, BMJ : British Medical Journal.

[14]  D. Baker,et al.  Income distribution and life expectancy. , 1992, BMJ.

[15]  John Lynch,et al.  Is income inequality a determinant of population health? Part 1. A systematic review. , 2004, The Milbank quarterly.

[16]  R. Waldmann,et al.  Income Distribution and Infant Mortality , 1992 .

[17]  A. T. Flegg,et al.  Inequality of income, illiteracy and medical care as determinants of infant mortality in underdeveloped countries. , 1982, Population studies.

[18]  I. Kawachi,et al.  Ecological Analysis of Teen Birth Rates: Association with Community Income and Income Inequality , 2001, Maternal and Child Health Journal.

[19]  J. Lynch,et al.  Inequality in income and mortality in the United States: analysis of mortality and potential pathways , 1996, BMJ.

[20]  R. Wilkinson,et al.  Adolescent birth rates, total homicides, and income inequality in rich countries. , 2005, American journal of public health.

[21]  Sharon Friel,et al.  Closing the gap in a generation: health equity through action on the social determinants of health , 2008, The Lancet.

[22]  D. Makuc,et al.  Health, United States, 2003; with chartbook on trends in the health of Americans , 2003 .

[23]  R. M. Woodbury.  Infant Mortality in the United States , 1936 .

[24]  D. Collison,et al.  Income inequality and child mortality in wealthy nations. , 2007, Journal of public health.

[25]  Ichiro Kawachi,et al.  Income distribution and mortality: cross sectional ecological study of the Robin Hood index in the United States , 1996, BMJ.

[26]  B. H. Kehrer,et al.  Impact of income maintenance on low birth weight: evidence from the Gary Experiment. , 1979, The Journal of human resources.

[27]  M. Kogan,et al.  Persistent Socioeconomic Disparities in Infant, Neonatal, and Postneonatal Mortality Rates in the United States, 1969–2001 , 2007, Pediatrics.

[28]  Alistair Woodward,et al.  National infant mortality rates in relation to gross national product and distribution of income , 1999, The Lancet.

[29]  T. To,et al.  Neighborhood income and health outcomes in infants: how do those with complex chronic conditions fare? , 2009, Archives of pediatrics & adolescent medicine.

[30]  E. Emerson.  Relative child poverty, income inequality, wealth, and health. , 2009, JAMA.

[31]  N. Sohler,et al.  Income inequality and infant mortality in New York City , 2003, Journal of Urban Health.

[32]  Susan E. Mayer,et al.  Some mechanisms linking economic inequality and infant mortality. , 2005, Social science & medicine.

[33]  The Impact of Inequality , 2005 .

[34]  Ichiro Kawachi,et al.  Income inequality and health: what have we learned so far? , 2004, Epidemiologic reviews.

[35]  N. Spencer.  The effect of income inequality and macro-level social policy on infant mortality and low birthweight in developed countries--a preliminary systematic review. , 2004, Child: care, health and development.

[36]  D. Weinberg,et al.  The Changing Shape of the Nation’s Income Distribution , 2000 .

[37]  Flegg At.  Inequality of income, illiteracy and medical care as determinants of infant mortality in underdeveloped countries. , 1982 .

[38]  S. Harper,et al.  Contextual effect of income inequality on birth outcomes. , 2005, International journal of epidemiology.

[39]  J. Currie,et al.  Chipping away at health: more on the relationship between income and child health. , 2007, Health affairs.

[40]  Irene Wennemo.  Infant mortality, public policy and inequality: a comparison of 18 industrialised countries 1950-85 , 1993 .

[41]  K. Fiscella,et al.  Poverty or income inequality as predictor of mortality: longitudinal cohort study , 1997, BMJ.

[42]  G. Singh,et al.  Infant mortality in the United States: trends, differentials, and projections, 1950 through 2010. , 1995, American journal of public health.

[43]  R. Wilkinson.  Unhealthy Societies: The Afflictions of Inequality , 1996 .

[44]  T. Blakely,et al.  When economists and epidemiologists disagree.... , 2001, Journal of health politics, policy and law.

[45]  S. Babones.  Income inequality and population health: correlation and causality. , 2008, Social science & medicine.

[46]  K. Bauman,et al.  Lower respiratory illness in infants and low socioeconomic status. , 1992, American journal of public health.

[47]  I. Kawachi,et al.  Social capital, income inequality, and mortality. , 1997, American journal of public health.