## 4 Discussion
### Mineral Content of Infant Formulas
#### 4.2.1 Differences in Mineral Content of Human Milk Relative to the Lactation Period  
Temporal changes in the concentration of minerals in HM are related to the changing nutritional needs of the infant. The content of macro- and microminerals and their mutual proportions significantly affect their absorption and utilization by the child's body [4]. Monitoring changes in the mineral composition of HM is crucial in composing IFs to have similar nutritional and functional properties [43]. Similarly, as reported by [PERSON] et al. [44], the mineral content of breast milk was as follows: K \(>\) Ca \(>>\) Na \(>\) Mg. The changes in the mineral content of HM according to the lactation period were similar to the results reported in previous similar studies, but some differences were noted in the present study.  
The Ca content in colostrum and transitional/mature milk was 27.75 \(\pm\) 5.34 mg/100 mL and 25.97 \(\pm\) 4.46 mg/100 mL, indicating values similar to those in the study by [PERSON] et al. [45] (24.536 mg/100 mL--colostrum; 28.08--transitional and mature milk. This study observed a decrease in P content as milk matures. P concentration is highest in early transitional milk and decreases as lactation progresses [6]. Mg content varied slightly with the lactation stage, as reported by [PERSON] et al. [4]. According to the literature, the concentration of Mg in breast milk ranges from 1 to 5 mg/100 mL, with a median of 3 mg/100 mL [6]. The concentration of Mg in breast milk is rather stable; however, some researchers report a slight increase or decrease in Mg during the first six months of lactation [6]. As for Na, according to WHO and the European Food Safety Authority (EFSA), the Na content in breast milk ranges from 6-17 mg/100 mL and 14-16 mg/100 mL, respectively [46]. In the present study, Na values were exceeded in colostrum relative to available standards. The Na content in our study decreased as lactation progressed, reaching a value 35% lower in transitional and mature milk than in colostrum, as in the work of [PERSON] et al. [45]. It should be noted that the level of electrolytes, especially Na, in breast milk can be dependent on external factors, including emotional stress [46].  
Among microminerals, significant differences between mineral content and lactation period were noted for Fe, Zn, and Mn. In our study, there was a decrease in Fe content relative to the lactation period, similar to that reported by [PERSON] and [PERSON] [5]. Fe content reaches a maximum level in colostrum and gradually decreases as the milk matures during the first year of lactation [47]. A Chinese cohort study indicated a decrease in Zn in breast milk as lactation progressed [43], while [PERSON] et al. [44] observed a 34% decrease in this element. In the study presented here, as much as a 50% decrease in Zn content was observed relative to the lactation period. The decline in Zn levels from colostrum to mature milk can reach as much as 4 mg per day in the first few days postpartum, decreasing to approximately 0.7 mg per day during the first six months of lactation [48]. [PERSON] et al. [49] report that the concentration of Zn in breast milk after three weeks of lactation is only 36-54% of the initial concentration, and after three months--only 20%. In the case of Mn, a higher amount was recorded in transitional and mature milk, the opposite of the study by [PERSON] et al. [45]. Differences in changes in the mineral composition of breast milk may depend on the individual variability of women and factors such as age and body mass index (BMI) [6].