Vinegar Co-ingestion in Type 2 Diabetes: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Vinegar Co-ingestion in Type 2 Diabetes (NCT01279317), a randomized na study. The primary outcome is Postprandial Glycemic Incremental Area Under the Curve.

2. Clinical Question

The study concerns an acute response after the intervention beverages, rather than a long-term clinical outcome. Its primary measure captures the extent of glucose elevation above the baseline concentration across the stated 2 hr period. The registry record identifies type 2 diabetes as the study condition and lists no secondary outcome measures. It does not report additional clinical questions or outcomes beyond the primary measure.

3. Trial Design

This was a randomized, single-masked crossover study sponsored by Maastricht University Medical Center. The registry record lists the study as completed, with enrollment of 12. The recorded start was 2010-09, and primary completion was 2011-03. The phase is listed as NA.

In a crossover design, participants receive more than one study condition, and outcomes under those conditions can be compared within the same people. This can help account for stable differences between participants. The registry record identifies a crossover model and randomized allocation, but does not report the sequence of conditions, how randomization was carried out, the interval between conditions, or whether any washout period was used. Those details are not reported in the registry record.

The two conditions were vinegar co-ingestion and placebo co-ingestion. For the vinegar condition, 25 ml vinegar was added to a glucose-containing beverage. For placebo, 25 ml vinegar was substituted by 25 ml water. The masking is listed as single, but the record does not identify who was masked or describe how masking was maintained.

The primary outcome was postprandial glycemic incremental area under the curve, measured over 2 hr after ingestion of the intervention beverages. The registry states that all subjects completed the study and were included in the analysis. The posted arm summaries contain 12 participants for each condition, while the registry’s analysis count is 0. No separate analysis methods, analysis population definition beyond the completion statement, or original sample-size justification is reported 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.

Before assignment: none applicable

Period 1

Washout

Period 2

Analysis population for the primary outcome, as defined in the registry: all subjects completed study and are included in analysis

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 Postprandial Glycemic Incremental Area Under the Curve, measured over 2 hr.

The primary endpoint is the incremental area under the plasma glucose concentration curve above baseline plasma glucose, measured over 2 hr following ingestion of the intervention beverages. The registry reports the unit as mmol/L / 2hr. Incremental area under the curve combines the height and duration of glucose elevation above the baseline into a single summary measure for the stated observation period.

This type of endpoint is used to describe the overall post-ingestion glucose response rather than relying on a single glucose measurement at one time point. It can represent whether glucose rises more, remains elevated longer, or does both during the measurement window. The word “incremental” matters: the area is calculated above the baseline concentration, rather than treating the baseline level itself as part of the response.

The posted outcome is continuous and is summarized using means with standard errors. That summary describes the average response within each condition and the uncertainty around each arm mean. The comparison gives the vinegar-minus-placebo mean difference and a confidence interval for that contrast. The registry record does not report the individual glucose measurements, the timing of any measurements within the 2 hr window, or the precise computational details used to derive the area.

7. Results Posted in the Registry

• Vinegar Co-ingestion: mean 739.00 versus 759.00 on control; difference -20.00 (95% CI -226.50 to 186.50), standardized effect d = -0.08; z-test p = 0.849.

8. Statistical Interpretation

9. Statistical Methods Explained

Several statistical summaries are useful for reading a continuous outcome such as incremental area under the curve. The registry reports an arm mean, a standard error for each arm mean, a mean difference, a confidence interval, and a p-value. Each answers a different question. None should be treated as a complete description of all participant responses.

What does the mean describe?

A mean is the arithmetic average of the observations in a condition. The posted means are 739.0 for vinegar co-ingestion and 759.0 for placebo co-ingestion. The reported mean difference is -20.0, with vinegar compared against placebo. The negative sign identifies the direction of the contrast under that ordering: the posted average is lower for vinegar. A mean can be useful for comparing groups or conditions, but it does not show whether responses were similar across participants or whether a few observations influenced the average.

The endpoint is continuous: it can take values across a scale rather than representing a simple event count. For continuous outcomes, differences in means are often a direct way to express how the average value differs between conditions. Interpretation also depends on the endpoint’s unit and definition. Here the measure is incremental area above baseline over 2 hr, and the listed unit is mmol/L / 2hr.

What does the standard error describe?

A standard error describes the estimated precision of a sample mean. If the same study were repeated under comparable conditions, sample means would vary; the standard error characterizes that sampling variability under the method used. It is not the same as the standard deviation of individual participant measurements. The arm standard errors are 74.0 for vinegar and 75.0 for placebo. The registry does not provide arm standard deviations directly, and it does not explain the method used to obtain the reported standard errors.

In general, uncertainty in a contrast depends on the variability of the outcome and on how observations are related. That point is especially relevant for a crossover study, where a participant contributes observations under multiple conditions. If the within-person responses are correlated, the uncertainty of a paired contrast can differ from the uncertainty calculated as if the conditions came from independent groups. The registry record does not state how that dependence was handled, so no particular method should be assumed.

How should the confidence interval be read?

A confidence interval gives a range of values that are reasonably compatible with the data and the statistical procedure used, under its assumptions. The reported 95% confidence interval for the mean difference extends from -226.5 to 186.5. Since this interval includes zero, the data do not distinguish the posted contrast from no mean difference at the conventional threshold implied by that interval. The interval also includes negative and positive values, so it allows for effects in both directions. It is not a guarantee that the true value lies within these particular endpoints, and it does not describe the range of individual responses.

Confidence intervals are often more informative than a p-value alone because they show both direction and precision. A narrow interval indicates greater precision for the contrast; a broad interval indicates less precision. Here the interval is broad relative to the point estimate, so the estimated difference is imprecise. The interval’s interpretation depends on the model and assumptions used, which are not detailed in the registry record.

What does the p-value mean?

The posted p-value is 0.849. In general, a p-value measures how unusual data at least as extreme as those observed would be under a specified null hypothesis and statistical model. A large p-value does not show that the null hypothesis is true, and it does not quantify the probability that a treatment effect exists. It also does not measure the clinical importance of a difference. The registry does not report the model, test, or decision threshold used for this comparison, so the p-value is best understood as a posted inferential statistic whose underlying analysis details are unavailable.

Over-dispersion is a general concern when observed variability is greater than the model expects. If variability is underestimated, standard errors can be too small and confidence intervals too narrow; if variability is accommodated appropriately, uncertainty estimates better reflect the data. The registry does not report a dispersion assessment or a model that would permit evaluating this issue. This is a general statistical consideration, not a finding about this study.

Why does the crossover design matter?

In general, crossover studies compare conditions within the same participants. Such comparisons can reduce the influence of stable participant characteristics, because each participant serves as their own comparator. However, the interpretation depends on design and analysis details, including condition order, period effects, possible carryover, and the relation between observations from the same person. The record names the crossover model and randomized allocation but does not describe those details or the statistical model. The reported arm summaries alone do not establish whether the comparison used a paired analysis.

The record states that all subjects completed the study and were included in the analysis. That is useful information about the reported primary analysis population, but it does not explain how outcomes were calculated, how repeated measurements were handled, or whether all data were complete at every measurement time. These details are not reported in the registry record.

10. Confidence Intervals and Precision

The reported 95% confidence interval for the mean difference runs from -226.5 to 186.5, around a point estimate of -20.0. This range is wide and includes zero. It also includes values below and above zero, so the posted data do not determine the direction of the population mean contrast with precision. The interval is more informative than the point estimate alone because it makes the uncertainty visible.

A confidence interval concerns uncertainty in an estimated quantity, not the distribution of individual participant outcomes. It does not mean that most individual responses fall between -226.5 and 186.5, nor does it provide a prediction interval for a future participant. The registry does not report individual-level observations or such a prediction interval.

The arm means were 739.0 for vinegar co-ingestion and 759.0 for placebo co-ingestion, with standard errors of 74.0 and 75.0, respectively. These standard errors refer to the estimated arm means. The registry also reports a pooled standard deviation of 258.1 for the comparison. The record does not explain whether or how this pooled summary incorporates the crossover pairing, and the standard errors should not be used to infer an unreported analysis method.

Precision is limited by the small enrollment of 12 and by the width of the reported interval. A result that is not statistically distinguishable from zero can reflect a truly small contrast, imprecision, or both. The available registry information cannot resolve those possibilities. The confidence interval should therefore be read as a statement about uncertainty in the estimated average contrast, not as proof of no effect.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. They are illustrations based on the observed effect, rather than a report of the trial’s original design calculation. The assumptions listed for these illustrations are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set to the stated fraction of the observed effect.

The 80% power column gives the illustrative number of participants per arm associated with an 80% chance of detecting the specified effect under those assumptions, if that effect were the true effect and the model assumptions held. The 90% power column gives the corresponding planning number for a 90% chance. These are planning concepts: power is the chance of detecting a specified effect under a particular design and set of assumptions, not a guarantee that a future study will reach a particular result.

The rows describe planning for 100%, 75%, and 50% of the observed effect. The displayed participant counts rise as the assumed effect becomes smaller: the smaller the effect researchers wish to detect, the more participants are generally required, all else being equal. Because these illustrations use an effect estimated in a small study, their figures are sensitive to that estimate and are not a substitute for a prespecified design calculation.

The values are not observed power. The original sample-size justification and the design assumptions used for this completed study are not reported in the registry record. The listed planning assumptions apply to the illustrations only, and should not be attributed to the trial’s original protocol.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -20.000; pooled standard deviation σ = 258.081.
2. n = 2 × (1.96 + 0.842)² × 258.081² / -20.000² = 2,613.9, rounded up to 2,614 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -20                      # observed difference in means
sigma <- 258.081382513346                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1279317)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 2,614 (80% power), 3,500 (90% power)
 75% of observed effect: n per arm = 4,647 (80% power), 6,221 (90% power)
 50% of observed effect: n per arm = 10,456 (80% power), 13,998 (90% power)
power.t.test: 2614.9 
Simulated power at n = 2,614 per arm: 0.799 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure and no secondary outcome measures. It reports one primary endpoint: postprandial glycemic incremental area under the curve. No multiplicity adjustment is reported, and the record does not state whether any additional outcomes, time points, subgroups, or analyses were examined outside the posted results. The absence of a reported adjustment should not be taken to mean that no multiplicity considerations existed in the study conduct; those details are not reported in the registry record.

The record states that all subjects completed the study and were included in the analysis. This supports a description of the reported primary analysis population, but the record does not provide participant flow details, exclusions, or a separate intention-to-treat definition. The analysis count is listed as 0 even though a primary outcome comparison is posted. The meaning of that registry count is not explained in the record, so it cannot be used to infer that no analysis was performed.

Missing-data handling is not reported in the registry record. The completion statement does not establish that every scheduled measurement was available for every participant or condition, nor does it explain how missing individual measurements, if any, were handled. The record also does not report imputation, sensitivity analyses, or the numbers with complete data by period and condition.

For a crossover study, the analysis may need to account for repeated observations from the same participant and potentially for period or sequence effects. The record identifies the crossover model but does not report whether these factors were included. It also does not provide a statistical analysis plan, interim analysis information, or a prespecified testing hierarchy. These omissions limit assessment of the analysis choices and of how the posted result relates to any planned analyses.

14. 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 lists 12 participants at risk in the vinegar co-ingestion group and 0 serious adverse events in that group. The record also lists 12 at risk for other adverse events and 0 events in that category. These figures describe the posted counts for the vinegar group; they do not by themselves establish the absence of harm or describe the full range of possible events.

No placebo-group adverse-event group is listed in the posted safety information. The registry therefore does not provide a corresponding placebo count for comparison. Deaths are not reported in the registry record. No serious adverse event terms are listed.

Safety counts depend on how events were defined, collected, and reported, and the record does not provide those details. With a small study, zero recorded events in a group should be read as the observed count in this study, not as proof that events cannot occur. The posted safety information is limited to the counts and categories described in the registry record.

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

The posted results describe a mean incremental area under the curve of 739.0 during vinegar co-ingestion and 759.0 during placebo co-ingestion. The reported mean difference is -20.0 for vinegar relative to placebo. This is the direction and size of the point estimate, not a definitive statement about the true average contrast.

The 95% confidence interval, from -226.5 to 186.5, includes zero and spans contrasts in both directions. The reported p-value is 0.849. Taken together, these statistics show that the posted estimate is imprecise and does not clearly separate the conditions under the reported comparison. They do not establish that the conditions are equivalent, that there is no possible difference, or that the true contrast is exactly the point estimate.

The study addressed an acute post-ingestion outcome measured over 2 hr in participants with type 2 diabetes. It does not answer questions about longer-term glucose control, other clinical outcomes, or use in populations not described in the registry record. The trial’s size and the uncertainty in the estimate also limit how much can be concluded from this single comparison.

The crossover design could support within-person comparisons, but the registry does not provide enough analysis detail to determine how pairing, period, sequence, or carryover were handled. The record also does not report a sample-size justification or a complete statistical plan. These gaps matter when judging how robustly the posted estimate reflects the design.

In short, the registry reports a lower point estimate for vinegar than placebo, alongside a wide confidence interval that includes both negative and positive values. That result is a description of the posted data and its uncertainty, not a treatment recommendation or a conclusion about clinical benefit.

16. Why This Trial Matters Statistically

This study is a useful example of why the direction of a point estimate and the precision of an estimate need to be considered together. The posted mean difference is -20.0, but the confidence interval extends from -226.5 to 186.5. Reporting only the point estimate would hide the substantial uncertainty around it; focusing only on whether a p-value crosses a threshold would also leave out the range of contrasts compatible with the data.

The crossover design adds an important statistical consideration. Comparisons within the same participant can account for stable differences between people, but a sound interpretation depends on how the repeated observations and possible period or sequence effects are handled. The registry identifies a crossover model without reporting the analytical details needed to assess those features. This illustrates why study design labels alone do not fully explain an estimate.

The record also shows the distinction between a completed study’s observed results and planning calculations based on those results. The planning illustrations use fractions of the observed effect and specified assumptions; they are not evidence about the trial’s original design or its probability of success. When the observed effect is uncertain, planning figures based on it should be treated as illustrative rather than definitive.

Finally, the registry’s limited analysis and safety detail highlights the value of transparent reporting. The completion statement, endpoint definition, arm summaries, contrast, and confidence interval provide useful information, but unreported features such as missing-data handling, masking details, and the analysis model leave important uncertainties. For clinical researchers and biostatisticians, this case emphasizes interpreting the estimates in light of both design and reporting completeness.

17. 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 study enrolled 12 participants, limiting the amount of information available for estimating the mean contrast. The confidence interval is wide, and the registry does not report a sample-size justification. The planning illustrations based on the observed effect do not establish what sample size was originally intended or why.

Although the design is identified as randomized and crossover, the registry does not describe allocation procedures, condition sequence, the interval between conditions, or any washout. It lists single masking but does not identify who was masked or how the masking was implemented. These details are relevant to assessing potential sources of bias and the interpretation of within-participant comparisons.

The statistical analysis method is not reported. In particular, the registry does not explain how the crossover structure, repeated observations, or possible period and sequence effects were handled. It does not provide a full analysis plan, missing-data methods, or details of outcome derivation beyond the endpoint description. The analysis count is listed as 0 even though a comparison is posted, and the record does not clarify this discrepancy in reporting.

The primary outcome is an acute measure observed over 2 hr. The registry record does not report longer-term outcomes or secondary outcomes. Safety information lists zero serious adverse events and zero other adverse events in the vinegar group, but no placebo safety group is listed and deaths are not reported in the registry record. The safety data are therefore limited and should be interpreted as recorded counts, not as a comprehensive comparative safety assessment.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Vinegar Co-ingestion in Type 2 Diabetes — NCT01279317.
• Registry record last updated 2011-10-03; status last verified 2011-08.
• Results first posted 2011-10-03.
• 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.

21. Record Summary

The registry record describes NCT01279317, titled “Vinegar Co-ingestion in Type 2 Diabetes,” sponsored by Maastricht University Medical Center. It is listed as a completed, randomized, single-masked crossover study with enrollment of 12 and phase NA. The recorded start was 2010-09 and primary completion was 2011-03.

The study compared a glucose-containing beverage with 25 ml vinegar against a placebo beverage in which 25 ml vinegar was substituted by 25 ml water. The primary endpoint was postprandial glycemic incremental area under the curve above baseline over 2 hr. All subjects completed the study and were included in the primary analysis, according to the registry.

The posted mean difference for vinegar relative to placebo was -20.0, with a 95% confidence interval from -226.5 to 186.5 and p = 0.849. Statistical analysis details, the original sample-size justification, and several crossover-design details are not reported in the registry record.