Association of breastfeeding duration with longitudinal changes in vertebral bone marrow, paraspinal muscle composition, and metabolic parameters in premenopausal women over five years

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Objective To investigate the association between breastfeeding duration and longitudinal changes in MRI-based proton-density fat fraction (PDFF) of vertebral bone marrow, paraspinal musculature (PSM), and metabolic parameters in premenopausal women. Methods Thirty-seven women (age 36.3 ± 3.8 years) were evaluated with the subgroups of women who breastfed ≤8 months vs. >8 months. All women underwent a 3 T MRI scan, including chemical shift encoding-based water-fat separation, postpartum (11.10 ± 2.38 months) and at 5-year follow-up. Glucose metabolism was analyzed at both visits using the updated Homeostasis Model Assessment (HOMA-2). PDFF values of lumbar and thoracic vertebrae and PSM were assessed, along with the cross-sectional area of PSM. Associations between breastfeeding duration and changes in bone marrow and muscle composition were assessed using multivariable linear regression models adjusted for age and body mass index (BMI). Results Women who breastfed >8 months showed a greater decrease in PDFF of the lumbar vertebrae (−9.62 ± 5.42 % vs. −4.69 ± 7.72 %; p = 0.03) and autochthonous muscles (AM) (−1.32 ± 2.52 % vs. 0.37 ± 2.48 %; p = 0.047) between baseline and 5-year follow-up compared to women who breastfed ≤8 months. Breastfeeding >8 months was significantly associated with greater reductions in both PDFF lumbar (β = − 5.34 %; p = 0.03) and PDFF AM (β = − 1.84 %; p = 0.03) independent of baseline BMI and age. Conclusion Longer breastfeeding duration is associated with a higher decrease of vertebral bone marrow adiposity and fat infiltration of autochthonous muscles over 5 years in premenopausal women, indicating potential benefits for maternal bone and muscle composition.