Background:
Childhood poverty heightens the risk of obesity in adulthood, but its effect during childhood is poorly understood. We analyzed the relationship between poverty trajectories across the ages of 6, 8, 10, and 12 years with BMI Z-scores and the risk of being overweight in a birth cohort of children.
Methods:
Data were from 703 participants in the 1998-2010 ″Quebec Longitudinal Study of Child Development″ (n=2,120) birth cohort. Household income was measured annually with poverty defined as income below the low-income thresholds established by Statistics Canada adjusted for household size and geographic region. Children’s height and weight at ages 6, 8, 10, and 12 years were measured by trained study staff. Body mass index (BMI) was converted to age- and sex- standardized BMI Z-scores and percentiles and were classified as overweight or obese (BMI percentile > 85th) based on CDC growth curves. Trajectories of poverty across the ages of 6, 8, 10, and 12 years were characterized with a latent class group analysis using maximum likelihood in a semiparametric mixture model. Multivariable linear regressions predicted BMI Z-scores at different ages, and logistic regression predicted the risk of being overweight or obese based on poverty trajectories after adjusting for sex. Because all children at ages 6 and 8 years were pre-pubertal, and all children at age 12 were in puberty, only the model for BMI at age 10 adjusted for puberty.
Results:
Poverty trajectories were fairly stable across time and fell into 1 lower exposure category (consistently low exposure (approximately 70%, n=487)) and 3 higher exposure categories (increasing: 8%, n=55; decreasing: 10%, n=70; or consistently high exposure: 13%, n=91)). After adjusting for covariates, compared to children experiencing lower exposure to poverty, BMI Z-scores of children with consistently high exposure to poverty were 0.05 (p=NS), 0.12 (p=NS), 0.37 (p=0.02), and 0.42 (p=0.003) higher at ages 6, 8, 10, and 12 years, respectively. After adjustment, children experiencing consistently high exposure to poverty were at a significantly increased risk for being overweight or obese at age 8 (OR: 2.0, 95% CI: 1.2-3.3, p=0.01), age 10 (OR: 2.1, CI: 1.2-3.5, p=0.005), and at age 12 years (OR: 2.8, CI: 1.7-4.7, p<0.001) compared to children experiencing lower exposure to poverty. Children experiencing decreasing exposure to poverty at all ages, or increasing exposure at age 10 and 12 years were at an increased risk for being overweight or obese, but the results were not statistically significant.
Conclusion:
Findings suggest that there is a latency period for the detrimental effects of poverty on weight, but that previous exposure can still impact future weight even at a young age. Whether the disparity in weight status according to poverty trajectories widens as the children continue to age should be investigated.
Cardiovascular disease in people born to unmarried mothers in two historical periods: The Helsinki Birth Cohort Study 1934–1944