摘要：Objectives. We estimated associations between poverty in early, middle, and later childhood and adult body mass index to further elucidate the effects of socioeconomic status on health. Methods. We conducted secondary analyses of data from men and women (N = 885) born between 1968 and 1975 who were tracked between their prenatal and birth years and adulthood in the nationally representative Panel Study of Income Dynamics. We used multivariate regression techniques and spline models to estimate the relationship between income in different stages of childhood and adult body mass index, overweight, and obesity. We controlled for other family characteristics, including income in other periods of childhood. Results. Mean annual family income in the prenatal and birth years for children whose annual family incomes averaged less than $25 000 was significantly associated with increased adult body mass index, but mean annual family income between 1 and 5 years of age and between 6 and 15 years of age was not. Conclusions. Our results indicated that economic conditions in the earliest period of life (during the prenatal and birth years) may play an important role in eventual anthropometric measures. The prevalence of overweight and obesity among US adults has reached alarming proportions, with a national average adult body mass index (BMI; weight in kilograms divided by height in meters squared) of 26.6 kg/m2 and rates of overweight and obesity at 34% and 30%, respectively. 1 Although morbid obesity is less common than overweight, rates have also risen over time, to a current prevalence of 4.7%. 2 These problems are costly to the affected individual, because overweight has adverse effects on morbidity, mortality, and earnings 3 ; excess body weight is the fifth most important risk factor contributing to the burden of disease in developed countries. Overweight and obesity are also costly for society: obesity is responsible for approximately 5% to 7% of total annual health care expenditures in the United States. 3 Given the high prevalence and high cost of adult excess body mass, it is important to identify the factors that predict adult overweight, particularly those factors that might be amenable to intervention. The key to preventing obesity and other health problems lies in the identification of modifiable risk factors. Socioeconomic conditions are consistent correlates of BMI. A large body of literature links adult socioeconomic conditions and adult BMI or weight gain in adulthood. 4 , 5 In developed countries, individuals with higher socioeconomic status are less likely to be overweight or obese. This inverse relationship between social class and BMI appears as early as 1 year of age. 6 Studies have established a gradient in adult BMI correlated with childhood social class (typically indexed by paternal occupation). 6 , 7 This research suggests an enduring role for early childhood socioeconomic conditions on adult BMI but does not provide clear implications for intervention, because it is not obvious how amenable fathers’ occupational status is to change. Early childhood income is a key predictor of later-life human capital outcomes. 8 However, it is uncertain whether low income during this childhood period also plays a uniquely important role in predicting body mass in adulthood. If we can identify the specific associations between income in childhood and adult health, there may be a greater chance of implementing targeted interventions for low-income children in the United States. Why might income in early childhood (the prenatal period to 5 years of age) predict overweight and obesity in adulthood? The fetal origins hypothesis posits a programming process whereby stimulants and insults during the prenatal period have long-lasting implications for physiology and disease risk. 9 Low income during the prenatal period may be associated with fetal undernutrition, low birth weight, or slow growth in the first 2 years of life. A pattern of small size at birth and low BMI at age 2, followed by rapid weight gain after age 2, is a risk factor for the development of insulin resistance and a disproportionately high fat mass in relation to muscle mass. Low income is also associated with food insecurity, 10 and some research shows positive cross-sectional associations between food insecurity and early childhood overweight status. 11 Other pathways could include the effect of low income in childhood on educational attainment or occupational status. Low-income children attain less education as adults, and education is an important determinant of health, in part through knowledge of a healthful diet and health-inducing behaviors. 8 Low-income children are also more likely as adults to work in lower-status occupations, in which social norms about thinness, healthful eating, and exercise habits may be less strong or in which opportunities for on-site exercise and healthful eating are less prevalent. 5 Low income in childhood may also be related to the early development and persistence of different social norms of eating, exercise, and overweight. Finally, low income in early childhood has been linked to poor physical and mental health in adulthood. Clearly, physical limitations may constrain the physical activity necessary to control weight. Poor mental health, such as depression, may lead to overeating, physical inactivity, or stress, all of which are associated with the development of excess body mass. Our goal was to estimate associations between early childhood income and later-life body mass. If such a link can be established, it will further support the case for early-life intervention. Several early-life interventions appear to provide practical and cost-effective approaches to promoting human capital development. 12 Interventions early in life may be an equally productive way to promote adult health.
