Measuring WIC’s Impact During COVID-19 and Beyond

Abstract

The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) is a cornerstone of the U.S. nutrition safety net, uniquely tasked with safeguarding the health of low-income pregnant and postpartum people, infants, and young children. Since its inception, WIC has evolved from a program focused on preventing undernutrition to one that also addresses overnutrition and diet-related chronic disease. While a substantial body of research links WIC participation to improved maternal and child health outcomes, findings for dietary intake, particularly among children, remain mixed. Moreover, prior evaluations have often focused narrowly on isolated outcomes, despite the program’s simultaneous intervention on dietary intakes, breastfeeding practices, nutrition literacy, and social/medical service access. In this dissertation, I aim to advance a more comprehensive understanding of WIC’s impact by examining dietary outcomes following a major pandemic-era policy change, developing and validating a multidimensional index to measure the WIC program’s impact, and evaluating how WIC’s impact has evolved over time. In the first study (Chapter 1), I examine dietary intake among 1–4-year-old Massachusetts children in households with low incomes following the 2021 increase to the WIC Cash Value Benefit (CVB) for fruits and vegetables. Using cross-sectional data from the Understanding Pandemic WIC-Waivers: Access, Redemption, Disparities (UPWARD) study (n=280), caregivers reported children’s dietary intake via a frequency-based screener and 24-hour recalls. Inverse probability weighted regression models were used to compare WIC participants to income-eligible nonparticipants. WIC-participating children consumed fruits 4.0 more times per week (SE: 1.2, p.01) and 0.6 cup-equivalents more fruits per day (SE: 0.4, p.001) than nonparticipants. They also consumed vegetables 2.5 more times per week (SE: 0.9, p.01), though there was no significant difference in vegetable intake (−0.02 cup-equivalents/day, SE: 0.3, p>0.05). There were no differences in total diet quality by WIC participation status. These findings suggest that the CVB increase was associated with higher frequency of fruit and vegetable consumption and greater fruit intake among WIC-participating children, though this did not translate to broader improvements in diet quality. In the second study (Chapter 2), I developed and validated the NHANES WIC Impact Index, a multidimensional measure designed to capture WIC’s influence across four domains: dietary intake, nutrition literacy, breastfeeding practices, and access to social and medical services. Using data from the National Health and Nutrition Examination Survey (NHANES), we evaluated reliability through item–item correlations and Cronbach’s alpha, and assessed validity through content, criterion, discriminant, and divergent approaches. The index demonstrated expected low internal consistency for a multidimensional construct (α=0.32–0.33) with item–item correlations supporting domain structure. The dietary domain was moderately correlated with HEI-2020 scores (r=0.58), indicating criterion validity. Among WIC-eligible children, prior participants scored 2.2 points lower on the index (95% CI: −3.9, −0.5; p.05) than current participants, while current participants and never-participants had similar scores (p>0.05). Scores were not associated with SNAP participation (p>0.05), supporting divergent validity. These results indicate that the WIC Impact Index is a reliable and valid tool for capturing WIC’s multidimensional impact on child health. In the third study (Chapter 3), we use the newly developed NHANES WIC Impact Index to monitor trends in WIC’s impact over time using a serial cross-sectional analysis of NHANES data from 2007–2018 (n=1,938 WIC-eligible children aged 2–4 years). Using a modified three-domain version of the WIC Impact Index (dietary intake, breastfeeding practices, and social/medical service access), we assessed temporal trends in total and domain-specific scores. Among current WIC participants, total and domain scores remained stable over time (p>0.05). In contrast, prior participants experienced small but significant declines in total score (−0.5 points, SE: 0.2; p=0.021) and dietary domain score (−0.3 points, SE: 0.1; p=0.007); no groups had significant changes in breastfeeding or social/medical service access domains. Among current WIC participants with the lowest incomes (% Poverty Income Ratio), there was also a modest decline in total score (−0.4 points, SE: 0.2; p=0.020). These findings suggest that sustained WIC participation may help maintain program-related health benefits over time, though additional support may be needed for the lowest-income participants. Together, these studies provide a comprehensive evaluation of WIC’s role in promoting child nutrition and health, highlighting both the program’s strengths and areas for continued improvement. By moving beyond single-outcome assessments and incorporating a multidimensional framework, this dissertation contributes to a more nuanced understanding of how WIC operates in practice.