Breastfeeding Duration and Bone Mineral Density in Childhood: A Prospective Study within GUSTO Cohort ^†

Nutrition contributes to bone mineral density (BMD) and plays a role in bone growth during infancy and childhood. However, the published relationships between breastfeeding exposure and BMD in infancy, childhood and adult life are not consistent. This cross-sectional study examined relationships of both breastfeeding duration and time of solid food introduction, with BMD in young Asian children from the Growing up in Singapore Towards healthy Outcomes (GUSTO) cohort.

Six-year-old children that were born healthy at term with available dual-energy X-ray absorptiometry (DXA) lumbar spine (LS) scans and data on the duration of any breastfeeding were included in the analysis (n = 207; 103 boys, 104 girls; 110 Chinese, 34 Indian and 63 Malay). LS bone mineral apparent density (BMAD), i.e., volumetric BMD, was estimated according to the published equation based on bone mineral content (BMC) and bone area from L2 to L4 (BMC/A_p ^3/2) [1]. Outcomes in univariable and multivariable linear regression models included areal BMD_LS (aBMD_LS) and BMAD_LS (to take account of bone size in growing children), and the standard deviation scores Z_LS-BMAD and Z_LS-aBMD. Covariates adjusted for were maternal ethnicity, pre-pregnancy BMI, child’s sex and both, child weight, and physical activity at 6 years of age.

Only 11 children were not breastfed, with the rest breastfed on average for 7.6 ± 11.5 (0.0–54.8) months. At 6 years of age, no significant difference in BMD_LS was detected by maternal ethnicity. Boys had lower BMD_LS compared to girls (aBMD_LS: −0.025 (95% CI: −0.040, −0.010; p = 0.002) g/cm²; Z_LS-aBMD: −0.436 (95% CI: −0.704, −0.168; p = 0.002) g/cm²; BMAD_LS: −0.008 (95% CI: −0.011, −0.005; p < 0.0001) g/cm³; Z_LS-BMAD: −0.621 (95% CI: −0.882, −0.360; p < 0.0001) g/cm³). In the univariable model, children with longer breastfeeding duration had significantly lower aBMD_LS, but not BMAD_LS (aBMD_LS: −0.0007 (95% CI: −0.001, −1.575; p = 0.045) g/cm²; Z_LS-aBMD: −0.012 (95% CI: −0.024, −0.0003; p = 0.045) g/cm²). In the analysis stratified by sex, the association with breastfeeding duration was significant only for girls and only for aBMD_LS (aBMD_LS: −0.001 (95% CI: −0.002, −0.0001; p = 0.037) g/cm²; Z_LS-aBMD: −0.018 (95% CI: −0.035, −0.001; p = 0.037) g/cm²). Adjusting for covariates resulted in no significant relationships with breastfeeding duration.

The average time of solid food introduction was reported as 5.5 ± 1.2 months (3.0–10.0; n = 188; 93 boys, 95 girls). No significant relationship with time of solid food introduction was found in the entire group in both the univariable and adjusted models. However, in stratified analysis, boys with later solid food introduction had lower BMD_LS (aBMD_LS: −0.009 (95% CI: −0.018, −0.0006; p = 0.037) g/cm²; Z_LS-aBMD: −0.166 (95% CI: −0.321, −0.010; p = 0.037) g/cm²; BMAD_LS: −0.003 (95% CI: −0.005, −0.0006; p = 0.011) g/cm³; Z_LS-BMAD: −0.205 (95% CI: −0.360, −0.050; p = 0.010) g/cm³). These relationships persisted when adjusting for covariates.

Breastfeeding duration and time of solid food introduction may have a long-term impact on bone mineralization in young children. However, a more precise quantitative approach when measuring breastfeeding exposure, such as 24 h infant milk intake and intake of milk components, would be prudent. Understanding the factors influencing bone remodeling during these periods of rapid skeletal growth is important for determining effective interventions to enhance bone development in vulnerable infants and children.