Inadequacy of calcium supplements to normalize muscle calcium deficiency in healthy subjects during prolonged hypokinesia.

Objective: We investigated the effect of hypokinesia (diminished movement) on muscle calcium (Ca(2+)) content with and without Ca(2+) supplementation and Ca(2+) loss with different muscle Ca(2+) deficiency; muscle Ca(2+) content, plasma Ca(2+) level, and Ca(2+) loss were measured.

Methods: Studies were performed in 40 physically healthy male volunteers during a pre-experimental period of 30 d and an experimental period of 364 d. Subjects in equal numbers were assigned to one of four groups: unsupplemented active control subjects (UACSs), unsupplemented hypokinetic subjects (UHKSs), supplemented active control subjects (SACSs), and supplemented hypokinetic subjects (SHKSs). A daily supplementation of 0.7 mmol of calcium lactate per kilogram of body weight was given to SACSs and SHKSs.

Results: Muscle Ca(2+) content decreased, and plasma Ca(2+) concentration and Ca(2+) loss in urine and feces increased (P < 0.05) in the SHKS and UHKS groups compared with their pre-experimental values and the values in their respective active control groups (SACS and UACS). However, muscle Ca(2+) content decreased more, and plasma Ca(2+) concentration and Ca(2+) loss increased more (P < 0.05) in the SHKS group than in the UHKS group.

Conclusion: Muscle Ca(2+) deficiency is more evident when Ca(2+) intake is higher and Ca(2+) loss is more exacerbated with higher than with lower muscle Ca(2+) deficiency, indicating that muscle Ca(2+) deficiency during prolonged hypokinesia is due to an inability of the body to use Ca(2+) but not to a Ca(2+) shortage in the diet.