Socioeconomic status and psychosocial or contextual factors related to the use of infant formula and follow-up milk: a survey among Japanese mothers

BACKGROUND: In Japan, the total fertility rate is declining and protecting children’s health is one of the most important health issues that the country has to face. Socioeconomic status (SES) and psychosocial or contextual factors are associated with the use and comprehension of food labeling information. Low SES is associated with high use of infant formula (IF), which is related to childhood obesity. This aim of this study was to examine the relationship between SES and psychosocial or contextual factors, and the appropriate use of IF and follow-up milk (FUM). METHODS: A web-based cross-sectional survey was conducted in January 2024 among 515 mothers of infants and young children living in Japan to investigate whether they were using IF and FUM appropriately, and whether they understood the difference between them. Not using the purpose-built spoon or hot water during preparation, providing IF or FUM to the child more than 2 h after preparation, adding any additional products to IF or FUM, or mistakenly using IF and FUM, interchangeably were considered instances of inappropriate use. Information on SES and psychosocial or contextual factors, including household composition, main occupation, and educational history, was also collected. Differences in SES and psychosocial or contextual factors were examined using the chi-square test or Fisher’s exact probability test. RESULTS: Adding other materials to IF or FUM was reported by 42.3% and 28.7% of the respondents, respectively. Among the respondents, 37.9% used IF for children over the age of 1 year aged over 1 year and 24.3% gave FUM to children under the age of 1 year aged under 1 year. Additionally, 1.8% of the respondents were unaware that IF is a breast milk substitute, whereas 13.2% were unaware that FUM is not. The use of IF and FUM differed significantly according to psychological stress (p = 0.034), household composition (p < 0.050), main occupation (p = 0.019), and educational history (p = 0.032). CONCLUSIONS: Psychological stress, household composition, main occupation, and educational history were associated with inappropriate use. Therefore, it would be beneficial to provide relevant targeted information about these products to caregivers.