Background: During lactation, women may lose up to 10% of bone mineral density (BMD) at trabecular-rich sites. Previous studies show that resistance exercise may slow BMD; however, the long-term effects of exercise on BMD during lactation have not been reported.
Objective: To evaluate the effect of two 16-week exercise interventions (4- to 20-wk postpartum) in lactating women at 1-year postpartum on lumbar spine, total body, and hip BMD.
Methods: To increase sample size at 1-year postpartum, two 16-week exercise interventions were combined for analysis. At 4-week postpartum, 55 women were randomized to intervention group (weight bearing aerobic exercise and resistance exercise) or control group (no exercise) for 16-week, with a 1-year postpartum follow-up. BMD was measured by dual-energy X-ray absorptiometry. Repeated-measures analysis of covariance was used to test for time and group differences for BMD controlling for prolactin concentration and dietary calcium at 1-year postpartum.
Results: Change in lumbar spine BMD was significantly different over time and between groups from 4-week to 1-year postpartum, when controlling for prolactin concentration and dietary calcium. There were no significant differences between groups in total body and hip BMD.
Conclusion: These results suggest that resistance exercise may slow bone loss during lactation, resulting in higher BMD levels at 1-year postpartum.
Keywords: breastfeeding; diet; vitamin D.