SMART model-based social marketing intervention to improve vitamin d supplementation adherence in female university students: a quasi-experimental mixed-methods study

Vitamin D deficiency is a growing public health concern among young women. Despite its essential role in bone health and immune function, behavioral barriers limit supplementation. This study evaluated the effectiveness of a social marketing intervention based on the Social Marketing Assessment and Response Tool (SMART) model in improving vitamin D supplementation behavior and Theory of Planned Behavior (TPB) constructs in female students at Yasuj University of Medical Sciences (YUMS). A quasi-experimental mixed-methods study was conducted in 2024. In the qualitative phase, 17 participants (5 nutrition experts, 2 health education specialists, 10 students) were interviewed using semi-structured guides. Data saturation occurred after 15 interviews, followed by two confirmatory interviews. Directed content analysis identified barriers and facilitators. In the quantitative phase, 224 students (112 intervention, 112 control) were assessed at baseline and one-month post-intervention using TPB-based questionnaires. The intervention, designed using social marketing components (product, price, place, promotion), included free supplement distribution, educational sessions, webinars, and digital materials. Data were analyzed using Mann-Whitney U and chi-square tests (P < 0.05). Qualitative analysis yielded 231 codes organized into 4 themes and 13 subthemes. At baseline, no significant differences existed between groups (P > 0.05). Post-intervention, all TPB construct scores were significantly higher with moderate to large effect sizes (r = 0.29-0.61, P < 0.0001). Regular supplementation increased to 92% (n = 103) versus 11.6% (n = 13) in controls (RR = 7.93, P < 0.0001). A SMART model-based social marketing intervention systematically addressing accessibility and facilitation barriers achieved substantial short-term improvements in vitamin D supplementation behavior. However, the study is limited by its one-month follow-up period and reliance on self-reported behavioral assessment. This theory-based, audience-centered approach provides a practical and replicable framework for promoting preventive health behaviors in university settings, though future research with objective biomarkers and extended follow-up is needed to confirm long-term sustainability.