Total duration of breastfeeding is associated with low bone mineral density in Iranian postmenopausal women

Background: Although transient bone loss has been described during and immediately after pregnancy and lactation, the association between breastfeeding and bone mineral density (BMD) after menopause remains controversial. Objective: To assess the association between breastfeeding and BMD in postmenopausal women in a population-based study. Materials and Methods: We randomly selected 245 healthy, free-living postmenopausal women, ages 40 to 80, from the Tehran Lipid and Glucose Study. The duration of breastfeeding was recorded. BMD was measured at the lumbar spine and upper femur by dual X-ray absorptiometry (Lunar DPXMD 7164). Multiple-linear regression was used to determine the association between the total duration of breastfeeding and BMD at different sites. Results: Means of age and years since menopause were 57.7 ± 7 and 9.4 ± 6.8 years, respectively. The mean number of parities was 5.1 ± 2.8. The median duration of breastfeeding was 48 months (25th to 75th percentiles: 24 and 108 months). Eleven percent of the women (n = 27) were osteoporotic in the femoral-neck region and 25.3% (n = 62) were osteoporotic in lumbar-spine sites. Breastfeeding duration was correlated inversely with femoral-neck BMD, Ward’s triangle, and L2-L4. After adjusting for age, BMI, years since menopause, number of parities, 25-hydroxy vitamin D, and LnPTH in the multiple linear regression analyses, breastfeeding duration was inversely associated with BMD at the femoral neck (R2 = 0.31; P = 0.02), Ward’s triangle (R2 = 0.32; P = 0.004), and L2-L4 (R2 = 0.18; P = 0.01), but not at other sites. Conclusions: In healthy postmenopausal women, BMDs of the femoral neck, Ward’s triangle, and the lumbar spine are inversely associated with the total duration of breastfeeding. A R T I C L E I N F O Article history: Received: 19 Nov 2010 Revised: 20 Dec 2010 Accepted: 1 Jan 2011