The Effects of Milk Supplementation on Bone Health Indices in Adults: A Meta-Analysis of Randomized Controlled Trials

Abstract

Milk contains a number of bone-beneficial nutrients. However, milk, due to the D-galactose content, might have unfavorable effects on bone health. A meta-analysis of randomized controlled trials (RCTs) was performed to clarify the effects of milk supplementation on bone mineral density (BMD), bone turnover markers [N-terminal telopeptide of type I collagen (NTx), C-terminal telopeptide of type 1 collagen (CTx), osteocalcin, bone alkaline phosphatase (BALP), and procollagen type 1N-propeptide (P1NP)], and hormonal indices related to bone metabolism [parathyroid hormone (PTH), 25-hydroxyvitamin D [25(OH)D], and insulin-like growth factor 1 (IGF-1)] in adults. The PubMed and Web of Science databases were searched. A random-effects model was used to estimate the pooled effect sizes. A total of 20 RCTs were included. The trial duration ranged from 1 mo to 36 mo. Milk supplementation resulted in a small but significant increase in BMD at the hip (+0.004g/cm2; n=9 RCTs) and lumbar spine (+0.025g/cm2; n=7), but did not significantly affect whole-body BMD (n=3) and femoral neck BMD (n=7). Milk supplementation reduced the concentrations of P1NP (-5.20ng/mL; n=9), CTx (-0.16ng/mL; n=9), and NTx (-8.66nmol bone collagen equivalents/mmol creatinine; n=3). The concentrations of osteocalcin (n=9) and BALP (n=3) were not affected by milk supplementation. Reduced parathyroid hormone PTH (-1.01 pg/mL; n=13) concentrations and increased IGF-1 (+1.79nmol/l; n=4) concentrations were observed with milk supplementation. 25(OH)D (+3.73 ng/mL; n=11) concentrations were increased with vitamin-D fortified milk supplementation. The addition of milk to the diet may potentially increase the likelihood of preventing bone loss by restoring bone homeostasis through the modulation of the calcium-vitamin D-PTH axis, bone remodeling rate, and growth hormone/IGF-1 axis.