Data from the National Health and Nutrition Examination Survey (NHANES) indicate that 14.0% of US children aged 2–5 years were overweight in 2006, compared with 4.0% in 1980 (ref. 1). Data such as these have hastened the recognition of obesity in US preschool children as a serious public health problem, and identifying its causes has become a major public health challenge for researchers, educators, and policy makers (2). Diet is naturally seen as a key determinant in the development, prevention, and treatment of childhood obesity (3). Because the consumption of sugar-sweetened beverages has substantially increased in the past 30 years, and these beverages are a major source of added sugars in children's diet, excess energy from the increased intakes of sugar-sweetened beverages may result in energy imbalance, further leading to obesity (4,5).
Previous studies provide conflicting evidence for a relationship between sugar-sweetened beverage consumption and childhood obesity. Several studies have identified a positive relationship (6,7,8,9,10,11), others have not (12,13,14,15,16,17,18,19,20), and still others have mixed findings (21,22,23,24). The current literature is limited by (i) inconsistent definition of sugar-sweetened beverages; and (ii) a lack of longitudinal studies examining association (15,16,23,25,26). In addition, there have been fewer studies targeting preschool children aged 2–5 years (9,12,16,19,25,27) compared to the number of studies targeting school-aged children 5–18 years of age (6,7,8,13,14,15,17,18,20,23). Although African-American children are represented in several of the national studies (15,17,19,27), results for low-income African-American children are generally limited in the literature.
The overall aim of the longitudinal study was to examine the association between consumption of sugar-sweetened beverages and obesity in a cohort of low-income African-American preschool children. In the investigation of these children, there were three basic questions addressed: (i) what is the relationship between consumption of sugar-sweetened beverages and BMI; (ii) what is the relationship between changes in consumption of sugar-sweetened beverages and change in BMI over a 2-year period; and (iii) what factors are related to the incidence (the occurrence of new cases) of overweight.
The first question adds to the literature on consumption of sugar-sweetened beverages and BMI findings from a group that has been under-studied. It is a particularly important group because obesity in adulthood are increasingly linked to childhood behaviors (28,29), and obesity in an African-American population, particularly women, is a public health concern (30,31).
The second and third questions are examinations of potential underlying causes of overweight and obesity. Each addresses the same issue, but from two different perspectives. The second question examines whether there is direct evidence among these young children whether increased or decreased consumption of sugar-sweetened beverages causes change in BMI. Such causal linkage is examined using the temporal aspect of these unique longitudinal data. The third question examines essentially the same issue, but does so from an “incidence of disease” perspective. The longitudinal features of the data allow the identification of new cases of overweight. Incidence can then be regressed on potential causal factors to determine whether an incidence investigation uncovers associations not observed in an analysis of change.