Response Letter to Drs. Kaloostian and Shil

Abstract

REFERENCES 1. Delbaere K, Close JCT, Heim J et al. A multifactorial approach to understanding fall risk in older people. J Am Geriatr Soc 2010;58:1679-1685. 2. Delbaere K, Close JCT, Brodaty H et al. Determinants of disparities between perceived and physiological risk of falling among elderly people: Cohort study. BMJ 2010;341:c4165. 3. Lord SR, Menz HB, Sherrington S. Home environment risk factors for falls in older people and the efficacy of home modifications. Age Ageing 2006; 35-S2:55-59. 4. Clemson L, Mackenzie L, Ballinger C et al. Environmental interventions to prevent falls in community-dwelling older people: A meta-analysis of randomized trials. J Aging Health 2008;20:954-971. 5. Sherrington C, Whitney JC, Lord SR et al. Effective exercise for the prevention of falls: A systematic review and meta-analysis. J Am Geriatr Soc 2008;56: 2234-2243. 6. Zijlstra G, van Haastregt J, Ambergen T et al. Effectiveness of a multifactorial,cognitive behavioral group intervention on fear of falling and associated avoidance of activity in community-living older people: A randomized controlled trial. evaluated the effects of vitamin D2 (1,000 IU/d) on muscle strength and mobility in postmenopausal women with baseline 25-hydroxyvitamin D (25(OH)D) concentrations of less than 24 ng/mL who were receiving calcium supplementation. The study found that the treatment significantly improved muscle strength and mobility in those who were weakest and slowest at baseline. Previous studies have shown markedly improved performance in speed and proximal muscle strength when 25(OH)D levels increased by even small amounts (4-16 ng/mL) and continued to improve as the levels increased to and beyond 40 ng/mL. 2 Based on current concepts, it is reasonable to expect that clinical research on vitamin D would be adjusted for renal function. The subject groups of the study conducted by Zhu and colleagues were not adjusted for renal impairments. The precursor to vitamin D, 25(OH)D is metabolized primarily in the kidney by the enzyme 25-hydroxyvitamin D-1a-hydroxylase to its active form, 1,25-dihydroxyvitamin D. 3 Therefore, if study groups were adjusted for chronic kidney disease, particularly those with a glomerular filtration rate of less than 30 mL/min per 1.73 m 2 of body surface area who can not adequately activate vitamin D were excluded, it would bring more strength to the evidence.Second, because the participants were all women aged 70 to 90 and were all postmenopausal, it is important to account for hormone replacement therapy (HRT), if any. Prior meaningful clinical trials have shown improvements in muscle strength with HRT. 4,5 In addition, some studies have shown protection of musculature from exercise-induced damage with HRT. 6 Although there have been some reports of no HRT effect on muscle strength, 7,8 it would be prudent for the authors to take the opportunity and adjust for HRT between the study groups. In light of current focus on vitamin D, better analysis would benefit proper and enhanced clinical use of vitamin D for patie...