The effect of daily exercise program on bone mineral density and cortisol level in preterm infants with very low birth weight: A randomized controlled trial.

•This study is the first in the literature to demonstrating the effect on the serum cortisol level of the exercise program.•The negative effect of serum cortisol on bone mineral density could be reduced by decreasing in stress of preterm infants.•The daily exercise program for preterm infants may be used to prevent preterm osteopenia and increase bone density.