The effects of exercise on bone density and hormones in lactating women

Abstract

The objective of this study was to determine the effects of exercise on bone‐related hormones in lactating women. At 4wks postpartum (PP) women were randomized to either exercise group (EX, n=10) [weight bearing aerobic exercise (3d/wk, 45 min/d) and 3d/wk of resistance exercise] or control group (C, no exercise, n=10) for 16 wks with a 1‐yr PP follow‐up. Lumbar spine (LS) and hip bone mineral densities (BMD) were measured by DXA. Prolactin (Prl), estradiol (E2), growth hormone (GH), insulin‐like growth factor (IGF‐1), and its associated binding protein‐3 (IGFBP‐3) were analyzed using ELISA. RMANOVA was used to determine differences between groups. During the intervention, C lost significantly more LS BMD then EX (−7 ± 2% vs −5 ± 1%, p < 0.01), but not hip BMD (−2 ± 3% vs −3 ± 2%). GH levels decreased in the C (2.2 ± 2.7 to 1.0 ± 1.6 μg/L) and increased in the EX (2.0 ± 2.7 to 4.0 ± 4.7 μg/L), p=0.1, with no change in IGF‐1 and IGFBP‐3. Prl levels declined in both groups during 1‐yr PP, whereas E2, GH, IGF‐1 and IGFBP‐3 levels remained stable in both groups. At 1‐yr PP, controlling for Prl levels, LS and hip BMD were within baseline values for EX (−1% and +0.4%, respectively) vs C (−4% and −2%), p=0.1. These results suggest exercise during lactation affects GH levels and given the role of GH in bone metabolism, may ultimately influence BMD.Supported by NC Agricultural Research Services