Can a heavy backpack make you shorter?

Using a backpack will not make you grow taller.

Factors that directly affect height are genetics and diet.

Things that influence muscular and skeletal development will affect posture and height or apparent height. Excessive or awkward weight carrying, whether in a backpack or otherwise, could affect these, but so can toxins in the environment, poor posture, lack of exercise and Arthritis.

Backpacks, when fitted correctly, can be used to help carry weight evenly and reduce stresses on the body.