Nitrate Supplementation and Exercise Tolerance in Patients With Type 2 Diabetes: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Nitrate Supplementation and Exercise Tolerance in Patients With Type 2 Diabetes (NCT02804932), a randomized na study. The primary outcome is Maximal Exercise Capacity (VO2max).

2. Clinical Question

The clinical question is framed around maximal aerobic capacity during cycle exercise testing. The study description also identifies skeletal muscle blood flow, mitochondrial function, and exercise capacity as areas of interest, but the registry does not provide results for those broader aims in the record. The primary endpoint is continuous, so an analysis could in principle compare group means or changes in means. The record identifies mean and standard deviation as the summary format, but does not report the endpoint values, the estimated difference, or its uncertainty. The clinical question therefore remains identifiable, while its answer cannot be inferred from the posted registry information.

3. Trial Design

The registry describes a completed, randomized, double-blind, parallel-group, placebo-controlled study. Enrollment is recorded as 54. The study dates run from 2016-08-15 to primary completion on 2019-12-20. These record details describe the planned study framework and timing; they do not establish what numerical effect was observed.

The intervention was nitrate-rich beetroot powder, described as beetroot crystals, given at 10g/day for 8 weeks. The comparator was beetroot powder without nitrate, also given for 8 weeks. The record names the products Super Beets and Super Beets Placebo. It does not give further details about the preparation, adherence, treatment allocation process, or how masking was maintained. Those details are not reported in the registry record.

The parallel design means the intervention and placebo are described as separate study arms rather than as a crossover sequence. Randomization and double masking are recorded, but the method used to generate or conceal the allocation is not reported in the registry record. The study also included nondiabetic control subjects. Their role should be distinguished from the randomized nitrate and placebo comparison: the record says they completed VO2max testing once, at the time point corresponding to the pre measurements for participants with type 2 diabetes. It does not describe them as a randomized treatment arm.

The primary endpoint was maximal exercise capacity, or VO2max, measured before and after 8 weeks of supplementation. The registry describes cardiopulmonary exercise testing on a cycle ergometer, with gas exchange measurements and a ramp protocol. Although the study is marked completed, no primary outcome results or analyses are listed in the registry record.

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

Analysis population for the primary outcome, as defined in the registry: One subject in the nitrate group did not reach maximal criteria during testing. Therefore, VO2max data was analyzed only in 18 participants in the nitrate group. Nondiabetic control subjects only completed VO2max testing once (same time point as pre measurements for T2D subjects).

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 Maximal Exercise Capacity (VO2max), measured over Pre and post 8 weeks of dietary nitrate supplementation.

The primary endpoint is maximal exercise capacity measured as VO2max, with units of mL/kg/min. VO2max represents the highest aerobic capacity reached during exercise testing. The registry describes a symptom-limited cardiopulmonary exercise test on a cycle ergometer using a ramp protocol, with gas exchange measured during the test and a 12-lead ECG. The endpoint is recorded as a continuous measure summarized using a mean and standard deviation.

As a general statistical explanation, a continuous endpoint retains information about the magnitude of measurements rather than sorting participants into categories. Comparing average values, or average changes, can therefore describe the size and direction of a group-level difference. A mean alone does not show how dispersed individual measurements are; the standard deviation describes that spread. Neither summary, by itself, establishes whether an observed difference is precise or compatible with a range of possible effects.

The timing is described as pre and post 8 weeks of dietary nitrate supplementation. The registry notes that one participant in the nitrate group did not reach maximal criteria during testing, and that VO2max data were analyzed only in 18 participants in that group. It also says nondiabetic control subjects completed VO2max testing once, at the time point corresponding to the pre measurements in the type 2 diabetes subjects. Endpoint results, including means and standard deviations, are not reported in the registry record. The stated measurement procedure explains what the endpoint was intended to capture, but does not supply evidence about the size or precision of any treatment contrast.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a continuous primary endpoint, VO2max, summarized as a mean with standard deviation and assessed before and after 8 weeks. It does not identify a statistical test, model, adjusted analysis, confidence interval, or p-value for that endpoint. The methods below explain general concepts that are relevant to this design; they should not be taken as a description of analyses actually performed.

What does a mean describe?

As a general explanation, the mean is a measure of the center of a set of continuous observations. A difference in means describes the average separation between groups or time points, depending on the comparison. The standard deviation describes the spread of observations around a group mean. A mean difference should be interpreted alongside its uncertainty and the variation in the measurements; the point estimate alone does not indicate how precisely the underlying effect has been estimated.

What would a confidence interval add?

As a general explanation, a confidence interval gives a range of values compatible with the data under a specified statistical procedure and its assumptions. It communicates precision as well as direction and magnitude. A narrow interval indicates greater precision than a wide interval, while either can include effects with different practical implications. The registry record does not report a confidence interval for VO2max, so the precision of the primary comparison is unknown.

How can pre-and-post measurements be compared?

As a general explanation, a trial with measurements before and after treatment can be analyzed by comparing post-treatment group means, comparing within-person changes between groups, or using a model that includes baseline measurements. These methods have different assumptions and may produce different estimates. A change score uses the relationship between a participant's baseline and later value; a baseline-adjusted model accounts for baseline measurements in estimating a treatment contrast. The registry gives the measurement timing but does not report which approach was used. No method should be attributed to the investigators without that information.

Because measurements from the same person over time are related, an analysis should account for that repeated-measures structure if it uses both time points. Treating such measurements as independent would disregard within-person association. This is a general design consideration, not a claim about the analysis in this study. The registry's lack of an analysis description means readers cannot assess whether the relationship between repeated measurements was modeled or whether the primary comparison used only one time point.

Why does the analysis population matter?

The record says one participant in the nitrate group did not reach maximal criteria during testing and that VO2max data were analyzed only in 18 participants in that group. That statement documents an endpoint-specific restriction, but does not fully define the analysis population. The registry does not report corresponding endpoint counts for the placebo group, reasons for any other unavailable measurements, or how missing values were treated. As a general explanation, excluding participants with unavailable measurements can affect the estimated group comparison if the reasons for missingness are related to treatment or outcome. The registry does not provide enough information to assess that possibility.

An analysis based on randomized assignment generally aims to preserve the comparison created by randomization, while an analysis limited to participants with usable measurements may differ from that target. The record does not say whether the primary analysis followed randomized assignment, whether participants were excluded after randomization, or whether sensitivity analyses were performed. These are not details that can be inferred from the reported study design.

What do planning illustrations mean?

As a general explanation, sample-size planning asks how many participants may be needed to detect a chosen effect under specified assumptions. The registry describes planning illustrations based on the observed effect, a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It also describes effects to detect as fractions of the observed effect. These are planning illustrations, not observed power, and do not establish that the trial was adequately powered for a particular clinical effect. The record does not report the investigators' own sample-size justification, so the illustrations should not be treated as the study's original design rationale.

The number of participants needed for a future study depends on the effect size considered important, the variability of the outcome, the desired error rates, allocation, and other design choices. As a general matter, calculations are conditional on their assumptions. An illustration based on an observed effect may be particularly uncertain when the observed estimate is itself imprecise. The registry does not provide the outcome estimate needed to assess that uncertainty alongside the planning calculations.

How should significance testing be understood?

As a general explanation, a p-value summarizes how unusual data at least as extreme as those observed would be under a specified null model and assumptions. It is not the probability that the null hypothesis is true, nor does it measure clinical importance. A p-value also cannot show the size or precision of an effect without an estimate and uncertainty interval. No p-value or test result for the primary endpoint is reported in the registry record.

Likewise, statistical significance is not the only relevant criterion for interpreting a trial. The size and precision of the effect, the endpoint's meaning, the analysis population, and the risk of bias all matter. Here, the unavailable endpoint results prevent an evidence-based assessment of those features for the primary comparison. The registry's design description can inform how the question was set up, but it cannot replace a reported estimate and analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures, but does not provide a statistical plan describing how multiple outcomes or comparisons were handled. It does not report a multiplicity adjustment, a hierarchy of hypotheses, or a prespecified strategy for selecting among endpoints. These details are not reported in the registry record. The primary outcome itself has several categories or time points and is not reduced to one comparison in the posted results.

As a general statistical explanation, testing multiple outcomes, time points, or contrasts can increase the chance of obtaining at least one apparently unusual result even when no underlying effects exist. Prespecifying a primary contrast and using an appropriate multiplicity strategy can help readers distinguish confirmatory analyses from exploratory ones. Without the statistical plan and the outcome-level analyses, it is not possible to determine how multiplicity was addressed in this study.

The registry notes that one nitrate-group participant did not reach maximal criteria and that VO2max data were analyzed only in 18 participants in that group. It does not report the complete analysis population across both randomized arms, participant flow for the endpoint, the reasons for unavailable measurements beyond this note, or the missing-data method. It also does not report whether the analysis used all randomized participants or a subset defined by endpoint availability. The implications of missingness therefore cannot be evaluated from the registry record.

Although the study is marked completed, analyses are not listed. The registry record does not report interim analyses, a statistical analysis plan, or a sample-size justification from the study team. These absences do not show that such procedures were not used; they mean the relevant information is not reported in the registry record.

11. 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.

The registry records serious adverse events in the nitrate, placebo, and nondiabetic control groups. For each group, the reported number affected by serious adverse events is 0, and deaths are recorded as 0. The record also reports 0 affected by other adverse events in each group. The corresponding numbers at risk are 20 for the nitrate group, 19 for the placebo group, and 15 for the nondiabetic control group.

These figures describe what was recorded for the groups and categories shown; they do not by themselves establish that no adverse events of any kind occurred. The registry does not provide serious-event terms, and the list of top serious terms is empty. Definitions, event-collection procedures, follow-up completeness, and details of how events were attributed or classified are not reported in the registry record. The distinction between no affected participants recorded and a guarantee that no events occurred is important.

Safety counts also do not provide a formal comparison of risk between the randomized arms. The record supplies no estimate of uncertainty for these counts and does not describe a statistical safety analysis. The nondiabetic control subjects are listed separately from the nitrate and placebo groups and should not be treated as part of the randomized treatment comparison on the basis of this record alone.

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

The registry record establishes that this study was designed to examine maximal exercise capacity before and after 8 weeks of dietary nitrate supplementation, with nitrate-free beetroot powder as the placebo comparator. It also documents a randomized, double-blind, parallel design and describes the exercise-testing procedure. These registry entries help define the clinical question and the intended comparison.

However, the record does not report VO2max results, group means, standard deviations, an estimated difference, a confidence interval, or a p-value. It therefore does not show whether the outcome differed between the nitrate and placebo arms, how large any difference was, or how precisely it was estimated. The absence of a posted analysis is not evidence that the treatments produced the same outcome. It is an absence of evidence in the registry record.

The measurement note matters: one participant in the nitrate group did not reach maximal criteria, and the record says that VO2max data were analyzed only in 18 participants in that group. Without full details of outcome availability and analysis methods, readers cannot determine how this restriction affected the comparison. The information about nondiabetic controls is also limited to their single VO2max test at the time point corresponding to the type 2 diabetes participants' pre measurements.

The safety record lists zero affected by serious and other adverse events in each group, and zero deaths. Those are registry-reported counts, not a complete description of event definitions, monitoring, or the precision of comparative safety estimates. They should not be extended beyond the categories and reporting shown in the registry.

In short, the available record supports a description of trial design and outcome measurement, but not a conclusion about the primary treatment effect or its clinical importance. A completed study label, enrollment entry, and planning illustrations cannot substitute for the missing outcome analysis. Any judgment about benefit, lack of benefit, or comparative safety would require results and methods that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial is statistically informative as an example of the distinction between a well-defined clinical question and a reported statistical result. The registry describes the randomized comparison, intervention duration, primary continuous endpoint, and measurement procedure. Those elements allow readers to understand what the investigators intended to compare. They do not reveal the effect estimate or its uncertainty.

For a continuous endpoint measured before and after treatment, the analysis must make clear whether the principal contrast concerns post-treatment values, within-person changes, or a baseline-adjusted comparison. The registry gives pre-and-post timing, but no method for combining those measurements. That omission matters because the estimand and precision depend on the analysis approach, as well as the observed data and their variability.

The endpoint-specific note about maximal criteria is also statistically relevant. The registry states that VO2max data were analyzed only in 18 nitrate-group participants after one participant did not reach maximal criteria. Without corresponding information across the other arm and a missing-data description, the composition of the analyzed groups is unclear. Readers cannot assess whether the reported analysis, if available elsewhere, would retain the randomized comparison or be vulnerable to selection related to outcome availability.

The record lists three outcome measures and no analyses, while the primary outcome includes several categories or time points and is not reduced to one comparison. This makes prespecification and multiplicity handling important to evaluate, yet those methods are not reported. The situation illustrates why an endpoint name alone is not enough: a transparent interpretation also needs the contrast, analysis population, model, estimate, uncertainty, and treatment of missing data.

Finally, planning illustrations based on an observed effect are distinct from the trial's original design justification and from observed power. Their assumptions can be useful for thinking about future study design, but they cannot answer what the current study found. The registry record therefore highlights the importance of complete reporting alongside careful design.

14. 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 limitation for interpreting this specific trial is that the registry record does not report the primary VO2max results or any analyses. There are no posted group means, standard deviations, effect estimates, confidence intervals, or p-values. Thus, the magnitude, direction, and precision of the primary comparison cannot be assessed.

The record identifies an endpoint-specific limitation: one participant in the nitrate group did not reach maximal criteria, and VO2max data were analyzed only in 18 participants in that group. It does not give full outcome counts for the placebo arm, explain whether other measurements were unavailable, or describe how the analysis handled missing data. The record also does not specify whether analysis followed randomized assignment or used an endpoint-available subset.

The nondiabetic control subjects completed VO2max testing once, at the time point corresponding to the pre measurements in the type 2 diabetes participants. The record does not provide a post-treatment measurement for these controls or describe their role in the primary treatment contrast. They therefore cannot be assumed to provide a parallel randomized comparison.

Further limitations of interpretation arise because the registry does not report the statistical analysis plan, the method used for the repeated measurements, a sample-size justification from the investigators, or an approach to multiplicity. It lists three outcome measures, while the primary outcome includes several categories or time points and is not reduced to one comparison. The record also gives limited detail about event definitions and safety follow-up. These are reporting limitations in the registry record; they do not establish what was or was not done during the study.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Nitrate Supplementation and Exercise Tolerance in Patients With Type 2 Diabetes — NCT02804932.
• Registry record last updated 2024-05-28; status last verified 2023-12.
• Results first posted 2024-05-28.
• 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.

18. Record Summary

The registry record describes a completed, randomized, double-blind, parallel, placebo-controlled study of dietary nitrate supplementation in patients with type 2 diabetes. Enrollment is recorded as 54. The nitrate intervention was beetroot powder at 10g/day for 8 weeks; the placebo was beetroot powder without nitrate for the same duration. Nondiabetic control subjects were also described.

The primary outcome was maximal exercise capacity, measured as VO2max in mL/kg/min before and after 8 weeks. The record describes cycle ergometer cardiopulmonary exercise testing with gas exchange measurements. It notes that one nitrate-group participant did not reach maximal criteria and that VO2max data were analyzed only in 18 participants in that group.

Three outcome measures are listed, but no analyses are listed and primary outcome results are not reported in the registry record. Serious adverse events, other adverse events, and deaths are recorded as 0 in each listed group. The available record defines the trial question and design, but does not provide a quantitative estimate of the primary treatment effect or its precision.