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Vitamin D supplementation does not influence muscle-related outcomes in children
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In vitamin D sufficient children and teens, 25-hydroxyvitamin D supplementation over 12 weeks did not influence changes in muscle mass, strength or composition, contradicting findings from similar studies conducted in adults, according to research published in the Journal of Bone and Mineral Research.
“The purpose of this ancillary analysis of a 12-week randomized, placebo-controlled vitamin D intervention was to determine if changes in vitamin D metabolites were associated with changes in muscle-related outcomes, including size, strength and composition in black and white, male and female children and adolescents,” Christian S. Wright, PhD, a postdoctoral research fellow at Indiana University School of Medicine, and colleagues wrote in the study background. “We hypothesized that increases in circulating 25-(OH)D concentrations would improve muscle-related outcomes following the 12-week intervention.”
Wright and colleagues analyzed data from 324 children aged 9 to 13 years who participated in the University of Georgia, Purdue University, and Indiana University (GAPI) 12-week vitamin D intervention (mean age, 11 years; 165 black participants; 162 girls). Researchers randomly assigned children to an oral vitamin D3 dose of 0 IU, 400 IU, 2,000 IU or 4,000 IU per day. Randomization took place after enrollment during the winter months (October through December) of 2009 and 2010-2011, when serum 25-(OH)D is at its lowest concentration. At baseline and 12 weeks, researchers evaluated 25-(OH)D, 1,25-dihydroxyvitamin D, intact parathyroid hormone and measures of total body composition, including fat-free soft tissue mass, muscle density and body fat percent, forearm and calf muscle cross-sectional area, intermuscular adipose tissue and handgrip strength. Dietary and exercise data were also documented for use as potential covariates.
The researchers conducted analysis of covariance, partial correlations and regression analyses of baseline and 12-week changes in vitamin D metabolites and outcomes of muscle mass, strength, muscle density and intermuscular adipose tissue.
Within the cohort, mean baseline 25-(OH)D concentration was 70 nmol/L; 13% of participants had serum 25-(OH)D less than 50 nmol/L, and 2% had serum 25-(OH)D less than 30 nmol/L. Researchers observed an increase in serum 25-(OH)D and 1,25-(OH)2D, but not in intact parathyroid hormone, during the course of the 12 weeks.
Researchers observed no association between serum vitamin D metabolites and muscle-related outcomes and baseline values or changes in dietary intake of calcium and vitamin D or exercise. However, baseline intact parathyroid hormone was positively associated with fat-free soft tissue (r = 0.145; P = .03) and forearm muscle cross-section area (r = 0.152; P = .022). During the intervention, researchers also observed increases in weight, BMI-for-age, fat mass, fat-free soft tissue, handgrip strength, forearm muscle cross-sectional area (P .001) and calf muscle cross-sectional area (P = .025).
Researchers observed a positive correlation between age and race and changes in fat-free soft tissue (age: r = 0.166; P = .005; race: r = –0.156; P = .008) and arm muscle cross-sectional area (age: r = 0.14; P = .019; race: r = –0.128; P = .031), as well as a negative correlation between changes in forearm intermuscular adipose tissue and changes in serum 25-(OH)D (r = –0.173; P = .029). In both adjusted and unadjusted analyses, changes in serum intact parathyroid hormone were positively associated with changes in forearm and calf muscle cross-sectional area and forearm and calf intermuscular adipose tissue.
“Increases in 25-(OH)D were correlated with decreases in forearm [intermuscular adipose tissue], whereas [intact parathyroid hormone] was positively associated and predicted changes in forearm and calf [muscle cross-sectional area] and [intermuscular adipose tissue] in this diverse, early adolescent population,” the researchers wrote. “Additional research is needed to clarify the relationship between 25-(OH)D and [intermuscular adipose tissue] accumulation, the influence of [intact parathyroid hormone] on muscle in early adolescence, and whether these are meaningful relationships.” – by Jennifer Byrne
Disclosures: The authors report no relevant financial disclosures.
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