The effects of muscle-building exercise on Vitamin D and mineral metabolism

Abstract

Exercise and muscle strength are important determinants of bone mass. Studies were carried out in normal young adult white males to determine the effects of exercise on vitamin D and mineral metabolism. Fourteen men who had engaged in regular muscle-building exercises for at least 1 year and 14 age-matched controls (age range, 19–36 year) were hospitalized on a metabolic ward and were given a constant daily diet estimated to contain 400 mg of calcium, 900 mg of phosphorus, 110 mEq of sodium, 65 mEq of potassium, and 18 mEq of magnesium. Body weight averaged 78 ± 3 kg in the exercisers and 72 ± 2 kg in the controls (NS). Serum calcium, ionized calcium, phosphate, magnesium, somatomedin-C, and immunoreactive parathyroid hormone (PTH) were not different in the two groups, whereas serum Gla-protein (39 ± 5 vs. 24 ± 2 ng/ml, p < 0.01), 25-hydroxyvitamin D (23 ± 2 vs. 16 ± 2, p < 0.05) and 1,25-dihydroxyvitamin D [1,25(OH)₂D] (40 ± 2 vs. 29 ± 2 pg/ml, p < 0.01) were higher in the exercisers than in the controls. Urinary calcium, phosphorus, sodium, potassium, creatinine clearance, and norepinephrine were not different in the two groups, whereas urinary magnesium (12.6 ± 1.0 vs. 9.4 ± 0.5 mEq/d, p < 0.01) and urinary cyclic adenosine 3′,5′-monophosphate (cyclic AMP) (2.52 ± 0.19 vs. 1.72 ± 0.20 nM/dl glomerular filtrate, p < 0.01) were higher in the exercisers than in the controls. There were positive correlations between serum 1,25(OH)₂D and urinary calcium (r = 0.544, p < 0.01) and between serum 1,25(OH)₂D and urinary magnesium (r = 0.407, p < 0.05) in all subjects. The results indicate that muscle-building exercise is associated with increases in serum Gla-protein, serum 1,25(OH)₂D, and urinary cyclic AMP. The increase in serum Gla-protein suggests that this form of exercise enhances bone formation.