Response to Tkachuk and Colleagues

To the Editor: We thank Tkachuk and colleagues for their interest in our article and would like to address their concerns.1 They contest our conclusion that “Twelve months after implementation of a 20,000-IU/wk vitamin D protocol for older adults in residential care, mean 25OHD concentrations were high, and there was no evidence of poor vitamin D status.” Their concern is lack of a control group. There are many randomized control trials demonstrating efficacy of weekly or bolus vitamin D at increasing 25OHD in older people. Our purpose was to report 25OHD concentrations in older adults in residential care 1 year after commencement of a once-a-week 20,000-IU vitamin D protocol; we did not infer causation, but it is hard to envisage any way other than through the supplement that these residents attained a mean 25OHD of more than 100 nmol/L. First, the few residents (n = 18) in our study that were not supplemented had a mean 25OHD concentration less than half those who were (43 vs 107 nmol/L). Second, unsupplemented older people in residential care in Toronto had a mean 25OHD of 39 and 45 nmol/L in March and August, respectively.2 Finally, in a national survey of noninstitutionalized Canadians, mean 25OHD was approximately 62 nmol/L in the summer for unsupplemented older people (aged 60–79).3 Our colleagues take exception to the use of 25OHD as a “surrogate marker.” Do they mean a surrogate marker of vitamin D or of falls and fractures? 25OHD is certainly a sound marker of vitamin D status, representing vitamin D from exogenous and endogenous sources. We did not suggest that 25OHD was a surrogate marker for falls and fractures. Falls and fractures are not surrogate markers for vitamin D deficiency. Our study was not designed to examine falls and fractures as outcomes. Perhaps had we used the terminology “composite vitamin D status marker” it may have been clearer; this was our intent. We believe the most important question that Tkachuk and colleagues pose is whether vitamin D supplementation reduces fall and fractures in elderly adults in residential care. The answer to this question appears to change with each systematic review. Our colleagues interpret the 2012 Cochrane review as showing no benefit of vitamin D in falls reduction.4 In our interpretation of this review, we found that, in studies in residential care (five trials with 4,603 participants), vitamin D supplementation significantly reduced the rate of falls, with a large effect size and a 95% confidence interval (CI) that comfortably excludes 1 (risk ratio (RR) = 0.63, 95% CI = 0.46–0.86). The RR for falls that Tkachuk and colleagues gave (0.55, 95% CI = 0.19–1.64) appears to be for vitamin D2 compared with placebo or standard care; we used vitamin D3. Our colleagues also cited a meta-analysis by Bolland and colleagues that found that vitamin D supplementation was unlikely to reduce risk of falls at the 15% threshold,5 but most of the trials included in this meta-analysis were of community-dwelling people, a population at lower risk of falls and fractures. Bolland and colleagues discount a less than 15% reduction, but even a modest 10% reduction in fall risk would mean several thousand fewer falls per year in Canada alone. On balance, we believe that the current evidence supports the use of vitamin D supplementation in residential care for achieving and maintaining vitamin D status with the potential for the reduction of falls and fractures. We found no evidence of hypercalcemia with vitamin D supplementation, a known harm caused by too much vitamin D, and concluded that the dose was safe. Our data thus fill an important knowledge gap in older adults. In the discussion, we explored some emerging evidence that high 25OHD levels were associated with greater mortality. These were observational studies, and to make more of this in the abstract, without context, would have been irresponsible. With respect to relevance to residential care, we meant in the context of those who have on average 18 to 24 months to live, but given most of the benefit from reduction in fall and fracture lies in moving a population 25OHD level from 30 to 80 nmol/L at most, it seemed prudent to reduce the dose; 10,000 IUs per week is not that different from the 1,000 IU/d that the American Geriatrics Society Workgroup on Vitamin D Supplementation for Older Adults recently recommended6 and is well under the 2,000 IU/d that Osteoporosis Canada indicates is safe and not requiring monitoring.7 If the evidence changes in the future, best practice guidelines and protocols should be revised accordingly. Conflict of Interest: The editor in chief has reviewed the conflict of interest checklist provided by the authors and has determined that the authors have no financial or any other kind of personal conflicts with this paper. Author Contributions: All authors: study concept and design. Green, Barr, Kitts, Feldman: obtaining funding. Feldman, Moore: project management. Moore, da Silva, Gaspard, Gustafson, Singh: acquisition of data. Hope A. Weiler's laboratory analyzed 25 hydroxyvitamin D. Green, Feldman: drafting initial manuscript. All authors: manuscript preparation, critical reviewed for important intellectual content. Sponsor's Role: None.

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