Influence of number of deliveries and total breast-feeding time on bone mineral density in premenopausal and young postmenopausal women

Objectives Pregnancy and lactation have been associated with decline in bone mineral density (BMD). It is not clear if there is a full recovery of BMD to baseline. This study sought to determine if pregnancy or breast-feeding or both have a cumulative effect on BMD in premenopausal and early postmenopausal women. Study design We performed single-center cohort analysis. Five hundred women aged 35-55 years underwent routine BMD screening from February to July 2011 at a tertiary medical center. Patients were questioned about number of total full-term deliveries and duration of breast-feeding and completed a background questionnaire on menarche and menopause, smoking, dairy product consumption, and weekly physical exercise. Weight and height were measured. Dual-energy X-ray absorptiometry was used to measure spinal, dual femoral neck, and total hip BMD. Main outcome measures Associations between background characteristics and BMD values were analyzed. Results Sixty percent of the women were premenopausal. Mean number of deliveries was 2.5 and mean duration of breast-feeding was 9.12 months. On univariate analysis, BMD values were negatively correlated with patient age (p = 0.006) and number of births (p = 0.013), and positively correlated with body mass index (p < 0.001). On multiple (adjusted) logistic regression analysis, prolonged breast-feeding duration, but not number of deliveries, was significantly correlated to a low BMD (p = 0.008). An effect was noted only in postmenopausal women. The spine was the most common site of BMD decrease. Conclusions Prolonged breast-feeding may have a deleterious long-term effect on BMD and may contribute to increased risk of osteoporosis later in life.