Breastfeeding Might Be Associated With Vitamin D and Cortisol Concentration Among Children Aged 6-13 Years

The aim of this study was to investigate if the type of feeding (breastfeeding/formula feeding) and the duration of breastfeeding (in months) may have long-term effects on vitamin D concentrations and cortisol levels in children aged 6-13 years. Additionally, we examined if family socio-economic status (SES) level modifies these relationships.

The analysis included 170 children (92 girls and 78 boys) aged 6-13 years. The study comprised a parental questionnaire and laboratory analyses. The questionnaire included information on the diet during the first months of life and the family's standard of living. The laboratory analyses measured 25(OH)D and cortisol concentrations in saliva using an ELISA assay. To evaluate the relationship between breastfeeding, vitamin D, and cortisol among children, several statistical tests were conducted, including the Chi2 test, the U-Mann-Whitney test, Kendall's Tau correlation, and multivariate and stepwise backward regression.

Breastfed girls had notably higher cortisol concentrations than boys (Z = 1.9885; p = 0.0468). In addition, for girls, there was a significant positive correlation between the length of breastfeeding and cortisol concentrations (τ = 0.2299). The concentration of cortisol was found to have a significant positive correlation with the concentration of vitamin D (τ = 0.1630). Breastfeeding duration (in months) was found to have a significant positive correlation with vitamin D concentration in males (τ = 0.1791). Furthermore, there was a positive correlation between the concentration of vitamin D and cortisol (τ = 0.2035). The multiple regression model revealed a significant positive correlation between breastfeeding duration (in months) and cortisol concentration in boys (Beta = 0.532; p < 0.0001). Additionally, a positive correlation was observed between cortisol concentration and vitamin D concentration in boys (Beta = 0.217; p = 0.0284). In contrast to boys, vitamin D concentrations in girls were found to have a positive correlation with the season of the study, specifically in late spring (Beta = 0.379; p = 0.0002). Additionally, backward stepwise regression indicated in boys a significant positive correlation between breastfeeding and cortisol levels (Beta = 0.620; p < 0.0001) and a positive correlation between cortisol levels and vitamin D levels (Beta = 0.222; p = 0.0247). Backward stepwise regression analysis also showed a significant positive correlation between vitamin D levels and high family SES (Beta = 0.258; p = 0.0250). In contrast to boys, only the vitamin D levels in girls showed a positive correlation with the season of the study, specifically in late spring (Beta = 0.385; p = 0.0002).

Breastfeeding is related to significantly higher levels of cortisol and vitamin D at ages 6-13 years. Additionally, higher SES of boys is associated with higher levels of vitamin D.