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

Milk contains a number of bone-beneficial nutrients. However, milk, due to D-galactose contents, 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 1 N-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 was ranged from 1 month to 36 months. Milk supplementation resulted in a small but significant increase in BMD at the hip (+0.004 g/cm2; n = 9 RCTs) and lumbar spine (+0.025 g/cm2; n = 7), but did not significantly affect whole body BMD (n = 3) and femoral neck BMD (n = 7). Milk supplementation reduced the levels of P1NP (-5.20 ng/ml; n = 9), CTx (-0.16 ng/ml; n = 9), and NTx (-8.66 nmol bone collagen equivalents/mmol creatinine; n = 3). The levels of osteocalcin (n = 9) and BALP (n = 3) were not affected by milk supplementation. Reduced parathyroid hormone PTH (-1.01 pg/ml; n = 13) levels and increased of IGF-1 (+1.79 nmol/l; n = 4) levels were observed with milk supplementation. 25(OH)D (3.73 ng/ml; n = 11) levels 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 calcium-vitamin D-PTH axis, bone remodeling rate, and growth hormone/IGF-1 axis.