The effects of single high-dose or daily low-dosage oral colecalciferol treatment on vitamin D levels and muscle strength in postmenopausal women.

Introduction: Vitamin D deficiency is a common health problem. Vitamin D supplements are used to improve vitamin D status; however, there are contradictory data related to what doses to give and how often they should be given. Many studies have investigated the effects of vitamin D supplementation on muscle strength, but the results remain controversial. We aimed to compare the effects and safety of single high-dose with daily low-dose oral colecalciferol on 25(OH)D levels and muscle strength in postmenopausal women with vitamin D deficiency or insufficiency.

Methods And Design: Sixty healthy postmenopausal women who had serum vitamin D levels < 20 ng/mL (50 nmol/L) were enrolled in the study. Group 1 (n = 32) was given daily oral dosages of 800 IU vitamin D3, and group 2 (n = 28) was given a single oral dose of 300,000 IU vitamin D3. Serum vitamin D levels and muscle strengths were measured at the beginning, 4th, and 12th week. Muscle strength tests were performed at 60° using a Biodex system 3 isokinetic dynamometer.

Results: Pretreatment vitamin D levels did not differ between the two groups (10.2 ± 4.4 ng/mL (25,4 ± 10,9 nmol/L); 9.7 ± 4.4 ng/mL (24,2 ± 10,9 nmol/L), p > 0.05). A significant increase in vitamin D levels was observed in both groups at 4 and 12 weeks after vitamin D3 treatment. The increase in the single-dose group was significantly higher than the daily low-dosage group at the 4th week (35.9 ± 9.6 ng/mL (89,6 ± 23,9 nmol/L), 16.9 ± 5.8 ng/mL (42,1 ± 14,4 nmol/L), p = 0.01). The increase in the single-dose group was significantly higher than in the daily low dosage group at the 12th week (23.4 ± 4.7 ng/mL (58,4 ± 11,7 nmol/L), 19.8 ± 7.2 ng/mL (49,4 ± 17,9 nmol/L), p = 0.049). The quadriceps muscle strength score increased significantly in the daily group at the 4th week (p = 0.038). The hamstring muscle strength score increased significantly in the daily group at the 12th week (p = 0.037).

Conclusion: Although daily administration routes are more effective in improving muscle strength, a single administration is more effective in increasing vitamin D levels.

Trial Registration Number: ISRCTN14226530 (04.07.2018), Name of the registry: ISRCTN registry, The study was retrospectively registered.