Abstract
Objective
Observational studies have suggested positive associations between serum 25-hydroxyvitamin D (25(OH)D) levels and muscular strength, balance and quality of life. Our aim was to examine whether high-dose vitamin D supplementation would improve these measures as compared to standard-dose vitamin D, as well as the possible muscular effects of Single Nucleotide Polymorphisms (SNPs) in genes encoding vitamin D-related enzymes.
Design
A 12-month randomized, double-blind, controlled trial where the participants received daily elemental calcium (1,000 mg) plus vitamin D3 (800 IU). In addition, the participants were randomized to receive either capsules with vitamin D3 (20,000 IU) or matching placebos to be taken twice a week.
Patients
297 postmenopausal women with osteopenia or osteoporosis.
Measurements
Muscle strength (handgrip and knee extensor strength), balance (tandem test) and quality of life (EQ-5D) were measured at baseline and after 12 months. The subjects were genotyped for SNPs related to vitamin D metabolism.
Results
Of the 297 included women, 275 completed the study. Mean serum 25(OH)D levels dramatically increased in the high-dose group (from 64.7 to 164.1 nmol/l; p<0.01), while a more moderate increased was observed in the standard-dose group (from 64.1 to 81.8 nmol/l; p<0.01). There was no significant difference between the groups in change in muscular strength, balance or quality of life over the intervention period. Polymorphisms in rs3829251 (located in the 7-dehydrocholesterol reductase gene) was associated with muscle strength and treatment effects.
Conclusion
One-year treatment with high-dose vitamin D had no effect on muscular strength, balance or quality of life in postmenopausal women with osteopenia or osteoporosis as compared to standard-dose. The association between rs3829251 and muscle strength needs confirmation in other populations
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