Vitamin D Supplementation Reduces Renin-Angiotensin System Activity in Obesity: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Vitamin D Supplementation Reduces Renin-Angiotensin System Activity in Obesity (NCT01068418), a na na study. The primary outcome is The Change in the Mean Arterial Blood Pressure in Response to an Infusion of Angiotensin II.

2. Clinical Question

The registry’s brief summary frames the work around whether vitamin D supplementation in obesity improves vascular sensitivity to angiotensin II. The primary endpoint addresses a blood-pressure response to that infusion; the secondary outcome addresses a renal blood-flow response. These are physiological measures, not direct comparisons of clinical events between treatment groups.

The trial title uses causal-sounding language about vitamin D and renin-angiotensin system activity, but the listed design is a single group without a randomized control. The registry record does not report the observed endpoint values or the direction and size of any change. The question can therefore be described from the aims and endpoint definitions, but the posted record does not establish whether either measured response changed after supplementation.

3. Trial Design

This was a completed, single-group study sponsored by Brigham and Women's Hospital. The registry lists an enrollment of 26, a start date of 2010-02, and a primary completion date of 2011-09. The intervention was vitamin D (cholecalciferol), described as vitamin D3 given at 15000IU daily in an open-label, single-arm design. The phase is listed as NA, allocation as NA, and masking as NONE.

There is no parallel control arm in the listed design. In this setting, the primary outcome is framed as a within-participant comparison across time: baseline and 1 month following vitamin D3 therapy. The registry lists the change in mean arterial blood pressure in response to an angiotensin II infusion as the primary outcome. The secondary outcome is the change in renal blood flow in response to an angiotensin II infusion.

The trial is marked COMPLETED, but that status does not itself provide the outcome findings. Results for the primary and secondary outcomes are not reported in the registry record. The posted information also does not describe the sequence or details of outcome assessments beyond the primary outcome timeframe, or specify how missing observations were handled.

The record does not report a sample-size justification, a prespecified statistical analysis plan, or interim analyses. These should not be inferred from the completion status, enrollment, or the analysis illustrations that accompany the page. Since the design has no like-for-like control comparison, changes observed over time would not by themselves distinguish an intervention effect from other explanations, such as time-related changes or measurement variation. This is a design consideration, not a claim about what happened to participants.

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

Reasons for not completing this period:

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 The Change in the Mean Arterial Blood Pressure in Response to an Infusion of Angiotensin II, measured over baseline and 1 month following vitamin D3 therapy.

The primary endpoint is the change in mean arterial blood pressure in response to an infusion of angiotensin II. It is measured in mmHg, summarized as a mean with standard deviation, and assessed at baseline and 1 month following vitamin D3 therapy. The endpoint therefore concerns a measured blood-pressure response to a physiological challenge rather than blood pressure in general or a clinical event.

As a general statistical point, a response measure can be useful when a study aims to characterize how a physiological system behaves under a defined stimulus. A before-and-after measure can show whether the recorded response differs across the assessment times. The mean summarizes the group’s average response, while the standard deviation describes variation among the observations; they answer different questions and should not be read interchangeably.

The registry record does not report the measured means, standard deviations, change estimate, or uncertainty interval for this endpoint. It therefore supports describing what was measured and when, but not describing the magnitude, precision, or direction of the observed change. The registry also does not provide further detail about the infusion procedure or the precise calculation used to derive the endpoint.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The methods that can be described from the registry record are limited to the design and outcome definitions. This is a single-group study, not a randomized comparison. The intervention is listed as vitamin D (cholecalciferol), and the arm description specifies open-label vitamin D3 at 15000IU daily. The primary endpoint is a continuous measure: change in mean arterial blood pressure in response to an angiotensin II infusion, reported in mmHg and summarized by a mean and standard deviation. The stated assessment times are baseline and 1 month following therapy.

What does a single-group comparison estimate?

As a general explanation, a before-and-after analysis describes the change observed in the participants measured at both times. It can be useful for describing patterns over time in a group, but it does not independently show what would have happened over the same period without the intervention. A comparator group can help address that question when its design and analysis make the groups sufficiently comparable. No comparator group is listed, and the record specifically notes that this is not a randomized comparison.

The registry does not specify the exact statistical test or model used to analyze the primary endpoint. It also does not report whether the analysis used paired measurements, how participant-level changes were summarized, or how missing or unusable measurements were handled. Although a paired approach is one general way to analyze repeated measurements on the same participants, it cannot be attributed to this study without a reported analysis method.

What do the mean and standard deviation describe?

In general, a mean describes the average observed value in a group. A standard deviation describes how spread out individual observations are around that mean. For a change outcome, the mean change and the spread of individual changes are not interchangeable with the means and standard deviations at each assessment time. The registry identifies mean and standard deviation as the parameter and dispersion for the primary outcome, but does not provide the observed values or clarify further how these summaries were calculated.

A confidence interval, as a general statistical concept, expresses uncertainty around an estimate under a specified method. A narrow interval generally indicates greater precision than a wide interval, but interpretation depends on the analysis and data. The registry record does not report an interval for the primary outcome. Nor does it report a p-value for that endpoint in the information. Without an estimate and its uncertainty, the direction and precision of the result cannot be assessed.

Why does over-dispersion matter?

In general, over-dispersion means that the observed variability is greater than a statistical model expects. If a model assumes less variability than the data contain, its uncertainty estimates may be too small and inferential results may be misleading. This is a general consideration rather than a finding about this trial: the primary outcome is continuous, and the registry record does not report an over-dispersion assessment or a model that would allow such an assessment.

How should the planning illustrations be read?

The sample-size illustrations use the observed effect as the basis for planning, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The displayed planning rows describe detecting a stated fraction of the observed effect. These are hypothetical design calculations, not the study’s observed power and not a description of the single-group design used in the registry. The illustration assumes two arms even though the trial record lists one group, so it should not be mistaken for an analysis of this trial’s actual allocation.

As a general point, planning calculations depend on the effect targeted and assumptions about variability, allocation, and the statistical method. A calculation based on an observed effect is not a substitute for a prospectively documented sample-size rationale. The registry record does not report such a trial-specific rationale, the assumptions originally used to plan enrollment, or the method used to determine the enrolled number of 26.

What remains unspecified?

The registry record does not report the statistical analysis plan, the exact analysis populations, the handling of missing data, or interim analyses. It does not state whether results were adjusted for other variables or provide details of the angiotensin II infusion and measurement procedures. These gaps limit the ability to reproduce the analysis or assess whether the posted endpoint definition matches the methods used. They should not be filled by assuming standard practice; different reasonable choices can affect estimates and uncertainty.

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 D3")
n   <- c(14)
m   <- c(1.97)
sp  <- c(5.14)
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 D3  14  1.970  5.140  -0.998  4.938

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and a secondary outcome, and reports 2 outcome measures and 2 analyses. The primary outcome concerns the change in mean arterial blood pressure in response to an angiotensin II infusion. The secondary outcome concerns the change in renal blood flow in response to an angiotensin II infusion. Outcome values and analysis details are not reported in the registry record.

When a study assesses more than one outcome, or conducts multiple statistical tests, multiplicity can affect how often at least one result appears statistically notable by chance. As a general explanation, a prespecified hierarchy, adjustment procedure, or clear distinction between primary and exploratory analyses can help readers understand how multiple results were handled. The registry record does not report a multiplicity strategy or identify any adjustment for multiple testing. It is therefore not possible to determine from this record how the two outcomes were treated together for inference.

The record also does not report the analysis populations or how missing data were handled. It does not state how many participants contributed measurements at each assessment, whether every participant had usable baseline and follow-up data, or whether any analysis excluded observations. Enrollment of 26 is not enough to establish the number analyzed for either endpoint.

In general, missingness can affect both the number of observations contributing to an estimate and the interpretation of that estimate. The implications depend on why measurements are absent and on the analytic approach. Neither the reasons for missingness nor the approach to it are reported in the registry record. As a result, readers cannot assess whether the outcome summaries, if reported elsewhere, represent all enrolled participants or a subset. No missing-data assumption or imputation method should be inferred from the outcome definitions alone.

12. Safety Results

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

Other (non-serious) adverse events

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

The registry’s serious adverse event summary lists 26 participants at risk in the Vitamin D3 group and 0 affected by serious adverse events. It lists 26 at risk for other adverse events and 0 affected. No top serious adverse event terms are listed. These are the figures recorded for this single group; there is no comparator group against which to contrast them.

As a general statistical point, a zero count in a posted summary means that no events are recorded in the specified category for the listed group. It does not establish that the underlying risk is zero, nor does it show that all possible events were captured or reported. Interpretation also depends on the observation period, event definitions, follow-up completeness, and collection procedures. Details of these are not reported in the registry record.

The registry describes the study as completed, but completion status does not supply additional safety follow-up information. The displayed figures should be read as a description of the record, not as a comparative estimate of safety. The record does not provide serious adverse event terms, and the absence of listed terms does not add information about events outside the categories or reporting shown.

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

This record establishes that a study examined vitamin D3 supplementation in obesity, with a primary outcome focused on blood-pressure response to an angiotensin II infusion and a secondary outcome focused on renal blood flow in response to that infusion. It also establishes the listed open-label, single-group design, daily dose of 15000IU, enrollment of 26, and primary assessment timeframe of baseline and 1 month following therapy.

It does not report the observed primary or secondary outcome values. The title’s wording about reducing renin-angiotensin system activity cannot be treated as a result. Without the outcome estimates, their variability or uncertainty, and the analysis details, the posted record does not show whether the measured responses increased, decreased, or remained similar. It also does not allow assessment of how precisely any change was estimated.

Even if a before-and-after change were reported, this design would describe a temporal change in the observed group rather than isolate an intervention effect through a randomized comparison. As a general matter, a control group can help distinguish an intervention-associated change from changes that would occur over time for other reasons. The registry record lists no such comparison, so causal attribution would require caution.

The result should also not be broadened beyond the endpoint. Mean arterial blood pressure in response to an infusion is a specific physiological measure. It is not itself a report of clinical events, and a renal blood-flow response is a distinct secondary measure. The registry record does not report outcomes beyond these measures in the listed result information, nor does it provide information to assess generalizability beyond the study population.

In practical statistical terms, this is a record of a defined research question and design, not a complete account of the numerical findings. The outcome conclusions, precision, and robustness are not reported in the registry record. Those omissions mean that the study’s measured responses cannot be interpreted from the posted information alone.

14. Why This Trial Matters Statistically

This study is statistically notable as an example of a question about physiological response assessed in a single group over time. The primary endpoint is defined around the response of mean arterial blood pressure to an angiotensin II infusion, with a baseline assessment and a follow-up assessment 1 month following vitamin D3 therapy. The secondary outcome concerns renal blood flow in response to the same type of infusion. These endpoints make clear that the research question concerns measured responses, not simply a general change in health status.

The design also illustrates why the distinction between description and causal inference matters. In a single-arm study, a comparison across time can describe the pattern in the enrolled group, but it cannot provide the same contrast as a concurrent control group. General methodological considerations include time-related changes, measurement variability, and expectations in an open-label setting. The registry does not establish that these influenced the findings; it does show that no like-for-like control comparison is listed.

A further statistical lesson is the importance of reporting estimates and uncertainty alongside endpoint definitions. The registry identifies the continuous outcome and its summary scale, but does not report the numerical result. Without an estimate and a measure of precision, readers cannot judge the magnitude or stability of a response. A study title or stated hypothesis cannot fill this gap.

The accompanying planning illustrations also offer a useful distinction between prospective design planning and retrospective calculation. They are described as illustrations based on an observed effect under specified assumptions, including a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They are not observed power and do not convert this single-arm study into a two-arm comparison. The registry record does not report the trial’s own sample-size justification.

For biostatistical interpretation, the record therefore underscores the value of complete outcome reporting: endpoint estimates, uncertainty, analysis populations, missing-data handling, and the analysis plan. Those elements are not reported in the registry record, limiting what can be concluded from it.

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 main trial-specific limitation is the single-group design. The registry explicitly notes that this is not a randomized comparison and that the arms are not a like-for-like control comparison. Consequently, any within-group change over time would not by itself establish that vitamin D3 caused the change. This limitation follows from the listed design and does not depend on an unreported result.

The study is open-label, with masking listed as NONE. The registry record does not describe blinded outcome assessment or further procedures that might mitigate the effects of knowing the intervention. The extent to which this matters depends on the measurement process, which is not described in detail. The record also does not report participant characteristics beyond the listed conditions and enrollment, limiting assessment of whom the findings might represent.

Outcome reporting is incomplete in the record. It defines the primary and secondary outcomes but does not report their numerical findings, variability, or uncertainty. Analysis methods, analysis populations, missing-data handling, multiplicity procedures, and interim analyses are not reported in the registry record. The lack of these details limits reproducibility and prevents a full assessment of statistical robustness.

The registry lists an enrollment of 26, but does not report a trial-specific sample-size justification. The planning illustrations on the page are not a substitute: they are based on an observed effect and assume two arms, whereas the listed trial design has a single group. The record also does not describe the duration or completeness of safety follow-up beyond the adverse-event figures shown. These limitations constrain interpretation of both efficacy-related measures and the safety summary.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Vitamin D Supplementation Reduces Renin-Angiotensin System Activity in Obesity — NCT01068418.
• Registry record last updated 2017-03-30; status last verified 2017-03.
• Results first posted 2017-02-14.
• 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

NCT01068418 is listed as a completed, open-label, single-group study sponsored by Brigham and Women's Hospital. The registry lists an enrollment of 26, with a start date of 2010-02 and primary completion date of 2011-09. The intervention is vitamin D (cholecalciferol), described as vitamin D3 at 15000IU daily.

The primary outcome is change in mean arterial blood pressure in response to an angiotensin II infusion, measured at baseline and 1 month following therapy. The listed secondary outcome is change in renal blood flow in response to an angiotensin II infusion. The serious adverse event summary lists 0 affected among 26 at risk.

Numerical outcome findings, the statistical analysis plan, sample-size justification, missing-data methods, and multiplicity procedures are not reported in the registry record. The planning illustrations are not observed power and do not represent the trial’s single-group design as a randomized comparison.