Pregnancy as one of the most important periods with commonly medical complications in women’s life, is associated with the enhancement of nutritional needs. Further, pregnancy influences the lifestyle and nutrition behaviors of women and their families (1). The malnutrition or inappropriate nutrition during pregnancy leads to a range of maternal and fetal complications, such as intrauterine growth restriction (IUGR), small for gestational age (SGA) (2), preterm delivery, premature rupture of membranes break, polyhydramnios, oligohydramnios, pre-eclampsia, spontaneous abortions, medically induced labor, fetal death, fetal distress, fetal growth restriction, and malformations (3).

The fetus meets all its needs from the mother during its growth and development and inadequate nutrients in the mother leads to the depletion of the body’s reserves and maternal weight loss (4, 5). The need for calcium in the diet increases during pregnancy and pregnant women, especially in the third trimester are at risk of calcium deficiency (6). Human pregnancy is associated with changes in calcium and bone metabolism, supporting the calcium transport between mother and fetus (7). Milk and dairy products are determinant in providing protein and calcium needed during pregnancy and preventing some complications, such as osteoporosis and tooth decay (8). Studies indicate that consuming more dairy products, such as milk dairy product during pregnancy may reduce the risk of newborn respiratory distress syndrome (9). Calcium deficiencies during pregnancy can lead to retardation of fetal skeletal growth and low level of calcium in the mother’s milk (10). Similarly, women who have experienced multiple births and did not receive adequate calcium intake may be at an increased risk of developing osteoporosis (11). A large number of studies indicated the significant role of calcium in preventing pre-eclampsia (11). Low calcium intake is associated with hypertensive disorders in pregnancy (12). Accordingly, calcium plays significant role in insulin resistant syndrome (13).

World Health Organization (WHO) and Food and Agriculture Organization (FAO) recommended dietary calcium intake of 1,200 mg/day for pregnant women (14). Some studies demonstrated that the calcium intake among Asian women is lower than the recommended values (15, 16) and the prevalence of calcium deficiency in different months of pregnancy varies from 19 to 33.5% among Iranian mothers (17, 18). A wide number of foods contain calcium, such as milk and milk products (providing 34–60% of calcium intake amongst adults) (19) and cereals and cereal products (providing 30% of calcium intake) (20). Milk and milk products are recognized as the main source of high bioavailable calcium with an average calcium content of 1,150 mg/L (21).

Research has shown that in various health-related behaviors such as nutritional behavior, interpersonal and certain social factors can play a pivotal role (22). While the World Health Organization has established nutritional and health guidelines for pregnant women these guidelines are implemented through healthcare systems, many of them fail to adequately account for interpersonal and social determinants of nutritional behaviors (23). Specifically, with regard to the nutrition of pregnant women, these guidelines have struggled to effectively improve the nutritional behaviors of this population, particularly in developing countries (24). Therefore, behavioral intervention about increased dairy product consumption seem to meet the extra needs of pregnant women. Recommendation for consuming calcium-rich foods includes a part of the routine health care of pregnant women in Iran (18). However, reaching sufficient amounts of calcium is still a challengeable issue among Iranian pregnant women (25).

Studies indicated that desirable nutritional behaviors can be promoted by improving self-efficacy, commitment to action, positive emotions related to behavior, the perceived benefits of performing the behavior, perceived sensitivity, perceived severity, and the reduction of perceived barriers among obese and overweight women (26). Pender’s health promotion model, including many of the afore-mentioned variables (27), can be effective for intervention among pregnant women. Based on the available evidence about the effectiveness of Pender’s health promotion model in nutritional behaviors, the model seems to be successfully used in improving calcium consumption behavior of pregnant women (26, 28). Therefore, the present study aimed to the effect of the social and interpersonal-based intervention on calcium consumption among pregnant women.

The mean age of participants in the control group was higher than that in the intervention group, with values of 27.19 ± 6.3 years and 30.77 ± 5.7 years, respectively; however, this difference was not statistically significant. Similarly, the mean gestational age was slightly greater in the control group (16.8 ± 3.2 weeks) compared to the intervention group (16.4 ± 3.7 weeks), but this difference was also not significant. In terms of blood pressure, the mean systolic blood pressure was 11.6 ± 0.8 in the control group, while it was 11.2 ± 9.0 in the intervention group, with no significant difference noted.

The distribution of variables was normal. There was no significant difference in income, gestational age, systolic and diastolic blood pressure at baseline between the groups. The difference in systolic blood pressure had no clinical value. There was no statistically significant difference between the groups at baseline (Table 1).

The Chi-square test indicated no significant differences in categorical demographic variables between the intervention and control groups at baseline. This includes age (≥28 years and < 28 years), education levels (illiterate: 33.3%; diploma and under diploma: 66.6%; academic education: 33.3%), employment status (employed vs. unemployed), spouse’s education, number of children, parity, and comorbidities (hypertension, diabetes, and cancer) (p < 0.05) (Table 2).

The independent sample t-test showed significant changes in the mean scores of knowledge (p < 0.001, t = 4.20), perceived benefits (p < 0.001, t = 6.26), barriers (p < 0.001, t = 6.87), self-efficacy (p < 0.001, t = 3.56), activity-related affect (p < 0.001, t = 4.70), situational influences (p < 0.001, t = 3.19), commitment (p = 0.001, t = 4.08), and immediate competing demands (p < 0.001, t = −3.99) before and after the intervention, except for spouse’s social support (p < 0.20, t = 1.28).

The results of the repeated measure ANOVA test at baseline indicated that the trend of changes independent of the effect of the two groups in the mean scores of knowledge (p-value = 0.001; F = 7.7), perceived benefits (p-value <0.001; F = 38.2), perceived self-efficacy (p-value <0.002; F = 6.4), activity-related affect (p-value <0.001; F = 25.08), interpersonal influences (p-value =0.043; F = 3.21), situational influences (p-value <0.001; F = 12.82), commitment to a plan of action (p-value <0.001; F = 25.43), and the construct immediate competing demands and preferences (p-value <0.001; t = −3.99) were incremental and significant from baseline to after the intervention over time (Table 3).

The repeated measure ANOVA also showed the studied variables were significantly different between intervention and control groups, regardless of time. Knowledge (p < 0.001, F = 17.15), perceived benefits (p < 0.001, F = 27.32), barriers (p < 0.001, F = 67.39), self-efficacy (p = 0.001, F = 11.97), activity-related affect (p < 0.001, F = 41.78), situational influences (p < 0.001, F = 24.96), interpersonal influences (p = 0.002, F = 10.21), commitment (p < 0.001, F = 14.32), and immediate competing demands (p < 0.001, F = 16.26) were significantly improved.

The interaction time × group effect was significant for all constructs of Pender’s HPM except for interpersonal influences construct. Table 3 illustrates the F- and p-value for the tests used for all constructs of Pender’s HPM.

Figure 2 displays the trend of changes in the mean score of constructs of Pender’s HPM in baseline, after intervention, and follow-up according to the control and intervention groups.

ANCOVA was used with adjustment of pre-test role to determine the effect of educational intervention based on Pender’s HPM on avarage calcium intake. The results showed that the intervention was effective and there is a significant difference in calcium intake (mg/day) between two groups (p < 0.001). (Table 4).

This study provides significant insights into the effectiveness of Pender’s Health Promotion Model (HPM) in enhancing calcium consumption among pregnant women, a demographic often overlooked in nutritional interventions. The educational intervention based on Pender’s Health Promotion Model effectively improved the model’s constructs, except for social support, and increased the calcium intake of pregnant women. The intervention significantly enhanced the women’s knowledge, perceived benefits, perceived barriers, perceived self-efficacy, activity-related affect, situational influences, commitment to a plan of action, and reduced immediate competing demands and preferences, both immediately after and 1 month later. Unlike previous studies that primarily focused on general dietary behaviors, this research specifically targets calcium intake, addressing a critical nutritional gap during pregnancy. The incorporation of social and interpersonal factors into the intervention design is particularly noteworthy, as it emphasizes the importance of contextual influences on dietary choices. This approach not only enriches the existing literature but also suggests that tailored educational strategies can effectively modify health behaviors in culturally specific settings, such as Iran.

Previous studies have also found that increasing perceived benefits and reducing perceived barriers can lead to improved self-efficacy in health behaviors, consistent with the findings of the present study (31). When compared to similar studies, our findings align with those of Vahedian Shahroodi et al. (32), who demonstrated that enhancing perceived benefits and reducing barriers significantly improved health behaviors among women. However, this study extends those findings by explicitly linking the constructs of Pender’s HPM to increased calcium intake, providing a more detailed understanding of how these constructs interact within the context of pregnancy. Furthermore, while many studies have reported improvements in general nutritional behaviors, our research uniquely quantifies the impact of a theory-based intervention on specific dietary outcomes, such as calcium consumption. This distinction highlights the potential for Pender’s HPM to serve as a robust framework for future interventions aimed at improving maternal nutrition, thereby contributing to better health outcomes for both mothers and their infants. Removing perceived barriers are an important factor in the process of self-care to perform healthy behaviors (33).

The self-efficacy of calcium consumption was improved through Bandura’s key strategies including mastery experiences, social modeling, verbal persuasion, and psychological responses (34). Participants were guided through step-by-step dietary changes, engaging successful pregnant women as role models, and receiving encouragement and feedback. Relaxation techniques addressed stress related to the behavior change. This multifaceted approach aligns with Bandura’s recommendations and is consistent with previous research (35). Vahedian Shahroodi et al. (32) similarly employed strategies such as lectures and self-monitoring to improve self-efficacy, while Wise et al. (36) found that involving pregnant women in healthy food preparation motivated their consumption. Studies have consistently demonstrated the predictive role of self-efficacy in shaping nutritional behaviors (37, 38).

The present study found that the activity-related affect score, reflecting feelings about performing the behavior, significantly increased in the intervention group after the intervention and during follow-up compared to the control group. This is significant, as Pender’s model suggests activity-related affect can explain 58% of the commitment to the behavior (39). Similarly, Goodarzi-Khoigani et al. (28) found a positive relationship between dairy consumption and Pender’s model constructs, which improved with educational intervention. The intervention addressed the negative feelings some mothers had towards milk consumption due to digestive issues, resolving their fear of potential consequences like vomiting, and thus improving their activity-related affect.

Interpersonal influences are defined as cognitions concerning the behaviors, beliefs, or attitudes that decide individuals’ predisposition to involve in healthy behaviors (40).

Interpersonal influences, such as social support from spouses, had limited impact on healthy behaviors after the intervention. The focus on emotional support was insufficient, and other forms of spousal support were less investigated. Cognitive and physiological factors may be more influential than spousal encouragement in adopting behaviors like consuming calcium-rich foods, due to issues like vomiting and taste preferences. The present study was in line with the study of Goodarzi-Khoigani et al. (28)in the field of interpersonal influences in performing the desired behavior.

Perceived barriers and situational influences were predictive of commitment to a plan of action. Consistent with the findings of Elseifi et al. (41) on breakfast consumption among students. The present study revealed that educational interventions, aimed at not consuming competitors and raising mothers’ knowledge of tempting situations to consume foods competing with calcium intake, can be effective until the follow-up period. However, some studies demonstrated no significant relationship between situational influences and oral health-related behaviors (42).

Commitment to the plan of action showed an increasing trend after the intervention and during follow-up. Previous studies demonstrated that performing the related behavior significantly improves among pregnant women with greater commitment to the use of supplements. Based on the results of the early studies, the greater the commitment of pregnant mothers to the use of supplements, the more significant the associated behavior (43).

Commitment, driven by an internal locus of control, can motivate individuals to adopt healthy behaviors despite obstacles (44). In the present study, the interventions could create an internal locus of control for individuals and increase their commitment to the implementation of the instruction.

Existing research has demonstrated that the desire to consume calcium-rich foods often competes with the intake of soft drinks, jam, ice cream, and other energy-dense, nutrient-poor foods (45). Previous studies have shown that interventions based on Pender’s Health Promotion Model (HPM) have been effective in addressing the role of immediate competing demands (46), although the study by Dehdari et al. (47) reported no significant change in this construct following the implementation of the intervention. Effective health promotion programs should focus on utilizing motivational strategies across various healthcare settings (48).

In our study, pregnant women were recommended to use calcium supplements and to take Vitamin D if they had a deficiency. Therefore, the values of calcium reported are solely related to food sources. Despite the intervention leading to an improvement of about 160 mg per day, the mean calcium intake remained below the recommended 1,200 mg/day for pregnant women. This confirms that supplementation is still necessary for pregnant women.

The use of nutritional outcomes, in addition to questionnaire data, provided an opportunity to evaluate the intervention’s impact in a clinical setting. Randomization in the allocation of participants to intervention and control groups improved the ability to control for confounding factors. All interventions were implemented according to the constructs of Pender’s Health Promotion Model.

Based on the results, Pender’s HPM can effectively improve the consumption behavior of foods containing calcium, such as milk and dairy products among pregnant women. All constructs of Pender’s HPM, except for interpersonal influencers, showed a significant increase after the intervention and in a one-month follow-up period. The amount of calcium intake of mothers increased after the three-month intervention period by improving Pender’s HBM constructs. Pregnant women should be empowered to make healthy behaviors, and appropriate health education interventions should be developed. Testing HPM is needed to support its predictive power in dairy behaviors. It also is suggested that health care providers use Pender’s HPM for other health-related behaviors.