Vitamin D Supplementation in Kidney Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Vitamin D Supplementation in Kidney Disease (NCT01229878), a randomized na study. The primary outcome is Change in Hip Flexor Strength.

2. Clinical Question

The study was designed as a pilot. Its stated aims also included assessing recruitment feasibility and evaluating whether the oral regimen could increase nutritional vitamin D levels safely and effectively. The registry lists quality-of-life self-assessment, neuropsychological assessments, and immune function assessments as secondary outcomes. These aims give the study a broader exploratory scope than the primary strength measure alone.

The posted outcome data describe the groups separately. They do not report an adjusted or unadjusted contrast between vitamin D and placebo, a confidence interval for that contrast, or a p-value. The record therefore supports a description of the recorded arm-level results, but not a conclusion about the magnitude or precision of a treatment effect. The planned question concerns supplementation added to usual care in this specific population; it is not a comparison of vitamin D against no treatment of any kind.

3. Trial Design

This was a randomized, parallel-group pilot study with placebo as the comparator. The registry classifies allocation as randomized and masking as quadruple. The brief study summary describes the study as double-blind; the registry record does not explain the difference between those masking descriptions. The study is marked completed, and its phase is listed as not applicable.

The planned population was hemodialysis patients with vitamin D deficiency who were already receiving routine intravenous vitamin D as part of standard care. The study summary describes assignment to oral cholecalciferol or placebo for 6 months. The oral regimen is described as 50,000 IU weekly. Both groups were therefore framed against the background of routine care, rather than as a comparison between vitamin D and the absence of vitamin D-related care.

The registry lists enrollment as 20. For the primary outcome, it reports 10 participants in the vitamin D arm and 6 in the placebo arm. These are the outcome-specific group counts, not an explanation of how all enrolled participants were handled. The reasons the outcome counts differ from total enrollment, and the number assigned to each arm at randomization, are not reported in the registry record. Safety reporting uses different group denominators, which are described separately in the safety interpretation.

The primary outcome was change in hip flexor strength from baseline to 6 months, expressed as percent change. The registry says strength was measured with a push-pull muscle strength dynamometer; participants performed the exercise 3 times at each visit, and the visit result was the average of those attempts. Secondary outcomes listed in the record include quality-of-life self-assessment, neuropsychological assessments, and immune function assessments. The specific instruments, detailed timing for all secondary measures, and analysis plan are not reported in the registry record.

The registry gives a start date of 2011-12-01 and a primary completion date of 2022-06-30. The sponsor is the VA Office of Research and Development. These administrative details describe the study record; they do not establish when particular participants were recruited or explain the length of the overall study period.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Change in Hip Flexor Strength, measured over 6 months.

The primary endpoint is change in hip flexor strength between baseline and 6 months, reported as percent change. Hip flexor strength is one component of physical function. The study used a push-pull muscle strength dynamometer, with participants performing the hip flexor exercise 3 times at each visit. The final value at each time point was the average of those 3 attempts. The endpoint is thus a change measure based on strength assessments at two visits, rather than a single measurement at follow-up.

Repeated attempts can help represent performance at a visit without relying on one effort alone. In general, muscle-strength testing can provide a direct quantitative measure of a physical function relevant to the study’s stated aims. The registry does not report the exact formula used to express change as a percentage, the device’s measurement properties, or the protocol details needed to assess reproducibility beyond the described repeated attempts and averaging.

The vitamin D group’s reported mean change was 20.34, with a standard deviation of 34.29, among 10 participants. The placebo group’s reported mean change was 6.83, with a standard deviation of 36.44, among 6 participants. The measure’s unit is percent change. These are separate group summaries; neither is itself an estimate of the difference between groups. The registry does not post a confidence interval or hypothesis test for the between-group effect.

Hip flexor strength addresses the physical-function aim, but it does not by itself represent cognition, quality of life, immune function, or the feasibility and safety aims. Those questions require their own outcomes and analyses. The registry lists several secondary outcome categories, but their results and analysis details are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary measure is continuous: each participant’s outcome is recorded on a numeric scale, and the registry summarizes each group using a mean and standard deviation. The group means are 20.34 for vitamin D and 6.83 for placebo. Their standard deviations are 34.29 and 36.44. The registry identifies the outcome unit as percent change and the parameter as a mean. These summaries describe the observed outcome values in each group, but they do not by themselves answer whether the groups differ beyond what could plausibly arise from sampling variation.

What does a mean describe?

In general, a mean is the arithmetic average of the observations included in a group summary. It gives a measure of the group’s central value, but it does not show how individual participants’ values are distributed. For example, the same mean can accompany tightly clustered observations or widely dispersed observations. In this study, the standard deviations add information about spread: larger standard deviations indicate more variability around the group mean. A standard deviation is not a confidence interval and does not directly quantify uncertainty in the estimated mean or in the difference between groups.

The reported outcome counts are 10 for vitamin D and 6 for placebo. The record does not state whether these counts represent every randomized participant with any available measurement, a complete-case subset, or a different analysis population. The registry enrollment is 20, but the record does not explain how the enrolled participants relate to the outcome-specific counts. That distinction is important when interpreting any group summary, because the participants contributing data determine what the estimate describes.

Why is a direct group comparison important?

In a randomized parallel-group study, a treatment-effect analysis generally compares outcomes between the assigned groups. For a continuous outcome, this can be expressed as a difference in group means or through a statistical model that estimates a treatment contrast. The contrast is the quantity that addresses whether the groups’ results differ, while a confidence interval communicates the range of effects compatible with the data under the analysis assumptions. A p-value, when reported, addresses the compatibility of the observed data with a specified null hypothesis; it is not a measure of effect size or clinical importance.

The registry presents arm-level means and standard deviations, but no between-group estimate, confidence interval, or p-value. It also lists 0 analyses. Consequently, the posted summaries do not support a reported inferential comparison. No new contrast should be inferred from the arm summaries in place of an analysis that the registry does not provide. A model might account for baseline values or other design features, but the analysis plan and whether such adjustment was used are not reported in the registry record.

What does variability mean for this outcome?

In general, over-dispersion means that observations vary more than a statistical model expects. For a continuous outcome, substantial spread can make the mean less precise, especially when the available group counts are limited. The standard deviations in this record show variation in the reported changes, but the registry does not state a probability model or report diagnostics. There is not enough information to determine whether a particular model’s assumptions were assessed or whether a different method was needed.

In general, a confidence interval combines an estimate with its uncertainty under a specified method. A narrower interval indicates greater precision under that method; a wider interval indicates less precision. The registry does not report an interval for the primary between-group comparison. Therefore, readers cannot use the record to judge the range of treatment effects compatible with the analysis, or to distinguish an imprecise estimate from a more precise one. The arm-level standard deviations are not substitutes for that missing interval.

How should planning calculations be understood?

In general, a sample-size planning calculation asks how many participants would be needed under stated assumptions to detect a prespecified effect with a chosen significance level and power. The record’s planning assumptions describe a two-sided significance level of 0.05, equal allocation, a normal approximation, and an effect expressed as a fraction of an observed effect. Such calculations are planning illustrations, not observed trial outcomes. They do not show the probability that the completed study’s result is correct, and they are not observed power.

The registry does not report the trial’s own sample-size justification or its assumptions for planning enrollment. The sample-size assumptions described for an illustration do not establish that those assumptions governed the study design. No numerical planning counts are stated in the registry record. The posted outcome summaries also lack a reported treatment-effect estimate, so they cannot be treated as a complete inferential result or as evidence of a prespecified target being achieved.

What details would clarify the analysis?

For a fuller statistical interpretation, the record would need to specify the analysis population, the primary statistical model, how baseline measurements were used, how missing outcomes were handled, and whether the analysis followed randomized assignment. It would also need to report a between-group estimate and its uncertainty. The registry does not report these details. The outcome description does give useful measurement information—the dynamometer, repeated attempts, averaging, and assessment time—but measurement detail does not replace a statistical analysis plan or result.

The primary outcome is only one of several aims and outcome categories. In general, analyses of multiple outcomes raise questions about multiplicity: the more hypotheses examined, the greater the chance that at least one result appears notable by chance if no adjustment or interpretive strategy is planned. The registry does not report a multiplicity strategy. Without posted secondary results or analysis details, it is not possible to determine how these outcomes were handled or whether claims were prioritized in advance.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Vitamin D", "Placebo")
n   <- c(10, 6)
m   <- c(20.34, 6.83)
sp  <- c(34.29, 36.44)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Vitamin D  10  20.340  34.290  -4.190  44.870
CARM  Placebo  6  6.830  36.440  -31.411  45.071

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 3 secondary outcome categories: quality-of-life self-assessment, neuropsychological assessments, and immune function assessments. It also lists 4 outcome measures overall, while 0 analyses are posted. The record does not describe a hierarchy among the outcomes, identify which secondary measures were prespecified for confirmatory testing, or report a strategy for addressing multiplicity. In general, when several outcomes are examined, the chance of at least one apparently unusual result can increase if each is interpreted without regard to the others. No adjustment or other multiplicity approach is reported in the registry record.

Missing-data information is also limited. The primary outcome counts are 10 in the vitamin D arm and 6 in the placebo arm, whereas total enrollment is listed as 20. The record does not explain the difference between these counts, identify how many participants had missing measurements, or state whether participants were excluded from the primary analysis. It does not report reasons for missingness, imputation, sensitivity analyses, or a rule for handling incomplete baseline or follow-up data. The different safety denominators are not an explanation for the primary outcome counts.

The analysis population is not reported in the registry record. It is therefore not possible to determine whether the primary summaries include all randomized participants, only participants with complete measurements, or another defined group. Nor does the registry state whether any analysis followed randomized assignment regardless of adherence. These omissions limit assessment of potential bias from missing outcomes or post-randomization exclusions. They do not establish that such bias occurred; they mean the record does not provide enough information to evaluate it.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: hospitalization (23.1%), er visit (14.3%), prolonged hospitalization (7.7%).

The registry reports serious adverse event counts using safety denominators of 13 for vitamin D and 7 for placebo. Serious adverse events affected 4 participants in the vitamin D group and 1 in the placebo group. No other adverse events are listed in either group, and deaths are listed as 0 in both groups. These figures describe the safety entries posted in the registry; they do not establish that every possible adverse event was assessed or reported.

The record lists hospitalization at 23.1%, ER visit at 14.3%, and prolonged hospitalization at 7.7% among the top serious-event terms. It does not clarify in this summary whether these terms overlap, how they map to the affected-participant counts, or which group each term occurred in. They should not be added together or treated as mutually exclusive categories based on the information reported.

The safety denominators differ from the primary-outcome counts, and the registry does not explain the difference. The entries also do not provide event timing, duration, relatedness to study treatment, severity grading beyond serious-event classification, or exposure-adjusted comparisons. In general, adverse-event counts need context about ascertainment and follow-up before they can be compared between groups. The posted figures are descriptive and do not establish a causal relationship between treatment and any event.

13. What the Result Does, and Does Not, Mean

The result means that the registry reports arm-specific summaries for change in hip flexor strength at 6 months. The mean percent change is 20.34 in the vitamin D group and 6.83 in the placebo group. The standard deviations are 34.29 and 36.44, and the outcome-specific counts are 10 and 6. These values describe the reported data; the record does not provide a direct estimate of the difference between arms or its precision.

The result does not establish that the treatment caused a change in strength. Randomization is an important design feature for comparing groups, but interpretation of a randomized trial still depends on the analysis population, missing data, adherence, outcome measurement, and the statistical comparison. Those analysis details are not reported in the registry record. Nor does the absence of a posted p-value show that the groups were equivalent or that there was no effect.

The result also does not answer every aim of the pilot study. Hip flexor strength is a physical-function measure; it does not by itself establish effects on cognition, quality of life, immune function, recruitment feasibility, or vitamin D levels. The registry lists secondary outcome categories, but does not provide their results in the record. Safety data are reported separately and should not be conflated with the efficacy outcome.

In general, a statistically clear result and a practically important result are different questions. Statistical precision concerns uncertainty around an estimated effect, while practical importance depends on whether the size and nature of the effect matter in the relevant setting. Here, no comparative confidence interval or test is posted, and the registry does not define a threshold for an important change in hip flexor strength. Thus neither statistical certainty nor clinical importance can be established from the arm-level summaries alone.

The study is identified as a pilot, and its aims include feasibility as well as outcome assessment. Pilot findings can inform the description and planning of later research, but the registry record does not report the study’s sample-size justification or a definitive comparative analysis. The posted figures should therefore be read as descriptive results from the reported outcome groups, not as a final determination about the effect of oral vitamin D supplementation.

14. Why This Trial Matters Statistically

This trial is statistically informative in part because it makes the gap between outcome summaries and a treatment-effect analysis visible. The registry reports a mean and standard deviation for each arm, but no direct comparison, confidence interval, or p-value. A reader can describe the arm-level results, yet cannot assess the uncertainty of a comparative effect from the posted record. That distinction is central to reading clinical trial results: separate group summaries are not the same as an estimate of the difference the randomized design was intended to examine.

The pilot context also matters. Enrollment is listed as 20, while the primary outcome summaries include 10 participants in the vitamin D group and 6 in the placebo group. The record does not explain the relationship between these counts. A transparent account of analysis populations and missing outcomes is important because incomplete outcome data can affect interpretation. Without those details, the appropriate response is to recognize the limitation rather than speculate about why the counts differ.

The study also lists several secondary outcome categories in addition to its primary physical-function outcome. This raises a general statistical question about how multiple outcomes are prioritized and interpreted. The registry does not report a multiplicity plan or post secondary analyses. Making those decisions explicit helps readers distinguish exploratory observations from prespecified confirmatory evidence.

Finally, the record describes a clinically specific comparison: oral supplementation or placebo on a background of routine intravenous vitamin D care in hemodialysis patients with vitamin D deficiency. That context defines what the trial was designed to examine. It does not make the posted arm summaries broadly generalizable, and the missing comparative analysis limits conclusions even within the studied population. The statistical lesson is to separate design, descriptive outcomes, inferential evidence, and what remains unreported.

15. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The outcome-specific counts are 10 for vitamin D and 6 for placebo, while the registry lists total enrollment as 20. The record does not explain this difference, identify the analysis population, or provide participant flow. It is therefore not possible to determine from the registry whether the primary outcome summaries include all randomized participants or how incomplete measurements were handled. The safety denominators are different again, and the record does not reconcile them with the outcome counts.

The registry posts arm-level means and standard deviations for the primary endpoint but no between-group estimate, confidence interval, or p-value. It lists 0 analyses. This prevents assessment of the precision of the comparative result and leaves unclear whether the summary values were adjusted for baseline strength or other factors. A statistical analysis plan, model details, and missing-data methods are not reported in the registry record.

The measurement description explains that a dynamometer was used, that participants performed 3 attempts at each visit, and that the attempts were averaged. However, the registry does not report the exact formula for percent change, measurement reliability, or criteria for valid testing. It also does not provide participant-level outcomes or distributional information beyond the standard deviations, so the pattern of individual changes cannot be assessed.

The study’s multiple aims and listed secondary outcomes create further interpretive limits. The registry does not report results for the secondary outcome categories, an outcome hierarchy, or a multiplicity strategy. The sample-size justification for the trial is not reported in the registry record. The registry also gives a quadruple masking classification, while its brief summary calls the study double-blind; the record does not explain that difference. These limitations leave important design and analysis details unresolved without indicating what occurred in practice.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Vitamin D Supplementation in Kidney Disease — NCT01229878.
• Registry record last updated 2025-08-22; status last verified 2025-08.
• Results first posted 2025-08-22.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

19. Record Summary

NCT01229878 is a completed randomized, parallel-group pilot study sponsored by the VA Office of Research and Development. The registry lists quadruple masking and enrollment of 20. The study concerns vitamin D supplementation in hemodialysis patients with vitamin D deficiency who were receiving routine care that included intravenous vitamin D. The study summary describes weekly oral cholecalciferol at 50,000 IU for 6 months versus placebo.

The primary outcome is change in hip flexor strength from baseline to 6 months, expressed as percent change and measured with a push-pull dynamometer. The vitamin D group has a reported mean of 20.34 and standard deviation of 34.29 among 10 participants; the placebo group has a mean of 6.83 and standard deviation of 36.44 among 6 participants. No comparative analysis is posted. The registry lists quality-of-life, neuropsychological, and immune-function secondary outcome categories. Analysis methods, missing-data handling, and a trial sample-size justification are not reported in the registry record.