This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for CARDIA-Salt Sensitivity of Blood Pressure (SSBP) (NCT04258332), a randomized na study. The primary outcome is Salt Sensitivity of Blood Pressure.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04258332 |
| Phase | NA |
| Condition | Salt Sensitivity of Blood Pressure, Hypertension |
| Allocation | Randomized |
| Design model | Crossover |
| Masking | None (open label) |
| Enrollment | 281 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Vanderbilt University Medical Center |
| Results posted | Yes |
2. Clinical Question
Population
Participants in a randomized dietary study concerning salt sensitivity of blood pressure and hypertension. The registry record reports enrollment of 281, but does not give more detailed eligibility criteria or describe the characteristics of the analyzed participants.
Intervention
A high-salt diet and a low-salt diet, each followed for one week. The high-salt intervention is described as supplementing participants’ usual diet with sodium bullion packets. The low-salt intervention is described as meals, snacks, and sodium-free water prepared through the study sites’ metabolic kitchens.
Comparator
Each participant’s blood pressure during the high-salt diet is contrasted with blood pressure during the low-salt diet. Participants were randomized to a diet sequence: high salt followed by low salt, or low salt followed by high salt.
Primary question
What is the within-person change in 24-hour ambulatory mean arterial pressure (MAP) between high- and low-salt diets, expressed as high-salt MAP minus low-salt MAP? The registry record describes the endpoint over 14 days total, with seven days on each diet.
The scientific motivation described in the registry record is that blood pressure can change with salt intake, while the mechanisms underlying this salt sensitivity are not completely understood. The study focuses on the blood-pressure contrast rather than a comparison of separate groups assigned to only one diet. Its crossover structure means that the endpoint concerns each participant’s measurements under both dietary conditions, with randomized order intended to vary which diet comes first.
The main reported summaries are separated by randomized sequence. That distinction matters: the two medians describe the within-person contrast in each sequence group, not a single pooled estimate of the contrast across all participants. The registry record does not report a pooled estimate or a direct statistical test comparing the sequence groups.
3. Trial Design
CARDIA-Salt Sensitivity of Blood Pressure (SSBP), also titled Dietary Sodium Inflammation and Salt Sensitivity of Blood Pressure, is a randomized crossover study sponsored by Vanderbilt University Medical Center. The registry record lists the study as completed, with an enrollment of 281. It records a start date of 2021-05-17 and a primary completion date of 2025-05-17. The phase is listed as NA.
Participants were randomized to one of two dietary orders: high-salt diet followed by low-salt diet, or low-salt diet followed by high-salt diet. Each diet period lasted seven days, for a stated total endpoint timeframe of 14 days. The design description emphasizes a within-person comparison of MAP across the two diets. In a crossover design, each participant contributes measurements under both conditions, while sequence identifies the order in which the conditions were experienced.
The registry record describes the high-salt diet as supplementation of the usual diet with sodium bullion packets. It describes the low-salt diet as a set of freshly prepared frozen meals, snacks, and sodium-free water, prepared in each site’s metabolic kitchen. The full protocol details are not reported in the registry record; the dietary descriptions available there are incomplete.
Masking is listed as none. The registry record does not report whether outcome assessors or analysts were masked. It also does not report a washout period, the timing of blood-pressure monitoring within each diet period, or procedures for assessing adherence. These details can matter when interpreting a crossover study because effects from an earlier period, changes over time, and differences in adherence may influence measurements in a later period.
The primary endpoint is reported separately for the two randomized sequence groups, with 118 participants in the high-salt-then-low-salt group and 95 in the low-salt-then-high-salt group. The registry record does not explain why these endpoint counts differ from each other or from the enrollment figure, or how participants without endpoint values were handled.
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: A total of 281 individuals consented (were enrolled). Of these 228 actually started the study, i.e., were assigned to a study group. The 53 that were consented/enrolled but did not start the study, either did not schedule study start dates, or no longer wanted to participate prior to assignment of study diet order. This study investigates salt-sensitivity of BP (SSBP), measured as change in BP between one-week of high-salt minus one-week of low-salt diet. SSBP was determined in 213.
Overall Study
| Stage | High Salt Diet Then Low Salt Diet | Low Salt Diet Then High Salt Diet |
|---|---|---|
| STARTED | 124 | 104 |
| COMPLETED | 118 | 95 |
| NOT COMPLETED | 6 | 9 |
Analysis population for the primary outcome, as defined in the registry: Participants were randomized to one of two arms: either a high salt diet first, then low salt diet, or low salt diet first then low salt diet. The goal of the study was to quantify the within individual change in mean arterial pressure between high- and low-sodium diet. Therefore, arms are presented according to randomized diet order rather than overall high- or low-sodium diet at any point. In total it took 14 days to complete the high- and low-sodium diets that lasted for one-week each.
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.
Population: As this was a cross-over trial, the number of baseline participants presented reflects those that completed the cross-over, rather than all enrolled.
| Characteristic | Unit | High Salt Diet Then Low Salt Diet | Low Salt Diet Then High Salt Diet | Total |
|---|---|---|---|---|
| Participants analysed | 118 | 95 | 213 | |
| Age, Continuous | years | 61 (56 to 64) | 61 (58 to 65) | 61 (57 to 64) |
| Sex: Female, Male: Female | Participants | 76 | 63 | 139 |
| Sex: Female, Male: Male | Participants | 42 | 32 | 74 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 75 | 61 | 136 |
| Race (NIH/OMB): White | Participants | 39 | 31 | 70 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 4 | 3 | 7 |
| Region of Enrollment: United States | participants | 118 | 95 | 213 |
6. Primary Endpoint
The registry lists the primary outcome as Salt Sensitivity of Blood Pressure, measured over 14 days total which is 7 days each of high- and low-salt diet.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Inter-Quartile Range |
| Unit | mm Hg |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is the change in 24-hour ambulatory mean arterial pressure (MAP) after one week on the high-salt diet compared with one week on the low-salt diet. It is calculated as MAP on the high-salt diet minus MAP on the low-salt diet and is expressed in mm Hg. A positive value therefore represents a higher measured MAP during the high-salt period than during the low-salt period for that within-person contrast; a negative value represents the reverse.
Ambulatory blood-pressure monitoring records measurements across a full day rather than relying on a single clinic reading. MAP is a summary measure of arterial pressure across the cardiac cycle. In this study, the endpoint was selected to quantify how blood pressure changed in relation to the two salt-intake conditions. The registry record identifies the endpoint statistic as a median and names the interquartile range as its dispersion measure.
The posted medians are 4.0 mm Hg for the high-salt-then-low-salt sequence and 3.2 mm Hg for the low-salt-then-high-salt sequence. The reported interval bounds are 0.3 to 7.0 and -1.2 to 8.8, respectively. Although the endpoint description names the interquartile range, the registry record does not identify what the posted interval bounds represent, and it does not give an interquartile range value for these summaries.
Because the endpoint is calculated within individuals, it differs from a comparison of the average or median MAP between two independent groups. Its interpretation depends on having measurements under both diet conditions and on how the paired data were analyzed. The registry record does not describe the analysis used to produce the posted summaries.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome is a median within-person MAP change, defined as high-salt MAP minus low-salt MAP. The median is 4.0 mm Hg in the sequence group assigned to high salt first, and 3.2 mm Hg in the group assigned to low salt first. Both point estimates are positive, so each reported group median represents higher MAP during the high-salt period than during the low-salt period. These group medians do not establish that every participant had a positive change.
The interval bounds differ across sequence groups. For the high-salt-then-low-salt group, the bounds are 0.3 to 7.0; for the low-salt-then-high-salt group, they are -1.2 to 8.8. The registry record does not report what kind of intervals these are, their confidence level, or the method used to calculate them. They therefore cannot be interpreted as confidence intervals on the basis of the registry record alone. In particular, it is not possible to use them to make a registry-supported claim about statistical significance or precision at a stated confidence level.
The outcome counts are 118 for the first sequence group and 95 for the second. The registry record does not explain the difference in these analysis counts, indicate whether they reflect missing measurements or other exclusions, or describe the analysis population. The overall enrollment figure is 281, but it should not be treated as the denominator for either median without further information about the analysis.
The endpoint is intended to summarize the within-person contrast across the two diets. The sequence-specific summaries are useful to see whether the reported contrast varies by order, but they do not by themselves establish an order effect. That would require a defined analysis comparing sequence groups or otherwise accounting for sequence and period. No such analysis is posted in the registry record, which lists no analyses.
The registry also lists no secondary outcome results. It does not report a p-value, a pooled treatment contrast, a standard error, or a model-based estimate for the primary endpoint. As a result, the posted information describes the observed medians and interval bounds but does not show how uncertainty was quantified or whether any formal hypothesis test was conducted.
These summaries describe measurements in this trial under its dietary conditions and study procedures. They do not identify the biological mechanism of salt sensitivity, and the endpoint alone does not establish the role of inflammation or any particular pathway. The registry background discusses possible mechanisms, but the primary result is a blood-pressure contrast rather than a direct test of those mechanisms.
9. Statistical Methods Explained
The primary outcome is a paired, or within-person, contrast: each participant’s MAP on the high-salt diet is compared with that participant’s MAP on the low-salt diet. A crossover trial can be efficient for this kind of question because stable differences between participants, such as their usual blood-pressure level, do not necessarily dominate a comparison based on each person’s change. The relevant analysis must still account for the structure of the repeated measurements and the order of the diet periods. The registry record does not describe the analysis method used.
Why report a median?
A median identifies the middle of an ordered set of observed values. It is less influenced by unusually large or small values than an arithmetic mean, so it can be a useful summary when data are skewed or contain outliers. The registry record specifies the median as the primary endpoint summary. It does not explain why that summary was selected or report the distribution of individual changes. The median alone cannot show how many participants had positive or negative changes, how variable individual responses were, or whether the distribution was symmetric.
What does the interval describe?
An interval places lower and upper bounds around a reported estimate or summary. In general, an interval can communicate uncertainty or describe a range of observations, but its meaning depends on how it was constructed. A confidence interval, for example, has a defined interpretation tied to a statistical procedure and confidence level. The registry record reports bounds for both sequence groups but does not state whether they are confidence intervals, interquartile ranges, or another type of interval. The endpoint description names the interquartile range as the dispersion measure, yet no interquartile range values are posted. The bounds should therefore be read as reported bounds without assigning them a statistical interpretation not stated in the record.
Why does sequence matter?
In a crossover design, treatment condition and period are linked to the randomized order. Participants in one sequence receive high salt first; participants in the other sequence receive low salt first. A comparison of sequence-specific summaries may help readers notice that the reported estimates differ, but it is not equivalent to a test of whether order influenced the outcome. A formal analysis could account for period, sequence, and the paired measurements, but the registry record does not say whether such an analysis was conducted or how it was specified.
Carryover is a general concern in crossover studies: an effect of an earlier condition might persist into a later period. A washout period can sometimes be used to reduce such concerns, depending on the intervention and outcome. The registry record does not report a washout period or a carryover assessment. This absence does not establish that carryover occurred; it means the record does not provide information for evaluating it.
What can be concluded from the posted summaries?
The medians describe the center of the observed within-person changes in each randomized sequence group. The interval bounds add information about the reported range around each median, but their statistical meaning is unspecified. Without the analysis description, interval definition, or a reported hypothesis test, readers cannot reconstruct the inferential procedure from the registry results alone. It is also not possible to tell whether the analysis used all eligible paired observations, adjusted for period or sequence, or applied other modeling choices.
The term over-dispersion refers generally to more variability in data than a chosen statistical model expects. When present, it can make standard errors too small if a model does not account for the extra variability. This concept can matter in count outcomes or other modeled data, but the primary endpoint is a continuous within-person MAP change, and the registry record does not report a model or any over-dispersion assessment. No claim about over-dispersion in this trial is warranted.
How should planning calculations be read?
Sample-size calculations based on an observed effect are planning illustrations, not evidence about the power achieved by the completed trial. The record’s stated assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect expressed as a fraction of the observed effect. These assumptions describe an illustrative planning approach; they do not establish that the trial was designed using that approach. The trial’s own sample-size justification and statistical plan are not reported in the registry record. No sample-size illustration should be interpreted as observed power or as a post hoc confirmation that the study could detect a particular effect.
For this endpoint, interpretation also depends on precision and analysis population. The registry reports sequence-specific counts and medians, but does not report the number of participants with complete paired measurements, the reasons for unavailable results, or how missing observations were handled. Those omissions limit assessment of whether the posted summaries represent all randomized participants or a subset defined by data availability.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists four outcome measures, but it posts no secondary outcome results. It lists no analyses. It does not report a prespecified statistical analysis plan, a hierarchy of outcomes, or any method for controlling multiplicity. Multiplicity arises when several outcomes, time points, subgroups, or comparisons are tested; without information about the planned analyses and any adjustment, the extent to which it was relevant cannot be assessed. The record does not establish whether the primary endpoint was the only formal hypothesis test.
For the primary endpoint, the record gives medians and interval bounds by randomized sequence group, but does not state how the intervals were calculated or provide a formal test. It does not report a pooled estimate, a test of sequence effects, or an adjusted analysis. The record also does not describe the statistical analysis population or the handling of missing measurements.
The posted endpoint counts are 118 in the high-salt-then-low-salt group and 95 in the low-salt-then-high-salt group, while the enrollment figure is 281. The reasons the counts differ are not reported in the registry record. It is not clear whether the difference reflects incomplete follow-up, missing paired blood-pressure data, exclusions, or another cause. The number of participants with measurements in both periods and the number included in each analysis are not described beyond the posted group counts.
Missing-data methods can affect a crossover result because a complete within-person contrast requires usable outcome information under both conditions. General approaches may include analyzing complete pairs or using a model that accommodates incomplete observations, but the registry record does not state which, if any, was used. There is also no report of sensitivity analyses assessing whether missing data could affect the conclusions.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| High Salt Diet | 0 | 217 | 0.0% |
| Low Salt Diet | 0 | 215 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| High Salt Diet | 0 of 217 |
| Low Salt Diet | 0 of 215 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| High Salt Diet | 21 of 217 |
| Low Salt Diet | 17 of 215 |
Most frequent non-serious adverse event terms
| Event term | Organ system | High Salt Diet | Low Salt Diet |
|---|---|---|---|
| Lightheaded | General disorders | 5 of 217 | 5 of 215 |
| Headache | General disorders | 6 of 217 | 3 of 215 |
| GI Upset | Gastrointestinal disorders | 6 of 217 | 3 of 215 |
| Cramp | Musculoskeletal and connective tissue disorders | 1 of 217 | 5 of 215 |
| Edema | General disorders | 6 of 217 | 0 of 215 |
| Oral symptoms | General disorders | 2 of 217 | 1 of 215 |
| Pain | General disorders | 2 of 217 | 0 of 215 |
| Dyspnea | General disorders | 1 of 217 | 0 of 215 |
| Diarrhea | Gastrointestinal disorders | 0 of 217 | 1 of 215 |
| Constipation | Gastrointestinal disorders | 0 of 217 | 1 of 215 |
The registry record reports serious adverse event counts of 0 for the high-salt diet group and 0 for the low-salt diet group. It reports 21 other adverse events in the high-salt group and 17 in the low-salt group. Deaths are reported as 0 in both groups. The listed numbers at risk are 217 for the high-salt group and 215 for the low-salt group for both serious and other adverse events.
These are descriptive counts, not comparisons adjusted for differences in exposure or participant characteristics. The record does not explain how adverse events were defined, whether the same participant could contribute more than one event, how events were attributed to a diet, or how long participants were monitored for safety. It also does not provide event descriptions for the non-serious counts. The list of top serious adverse-event terms is empty, consistent with the reported zero serious-event counts, but does not provide broader information about how safety events were collected.
Zero reported serious adverse events means none were recorded in these registry group summaries; it does not establish that a risk is absent. The safety counts should be interpreted in light of the study’s duration, definitions, and monitoring procedures, details that are not reported in the registry record.
12. What the Result Does, and Does Not, Mean
The primary result describes the median change in 24-hour ambulatory MAP between high- and low-salt diet periods. The reported median is positive in each randomized sequence group: 4.0 mm Hg in the high-salt-then-low-salt group and 3.2 mm Hg in the low-salt-then-high-salt group. These values summarize the center of the within-person changes in the analyzed participants in each group, as reported by the registry. The posted results do not show that every individual had the same direction or magnitude of change.
The results do not establish whether the difference between the two sequence-specific medians is meaningful or statistically distinguishable. The registry record does not identify the interval bounds, report a confidence level, or provide a hypothesis test. Nor does it report a pooled estimate across sequence groups. Without those details, the available summaries do not support a precise statement about the uncertainty of the overall within-person contrast.
The study’s background discusses potential links between sodium, inflammation, immune responses, and blood pressure. The primary endpoint measures MAP, not those biological processes. The posted endpoint summaries therefore do not demonstrate a mechanism or establish that any particular inflammatory pathway explains the observed blood-pressure changes.
The study is a randomized crossover trial, but the registry results do not describe the analysis sufficiently to determine how period, sequence, missing observations, or possible carryover were handled. The endpoint counts are smaller than the enrollment figure, and the reasons are not reported. Those uncertainties limit assessment of how broadly the posted summaries represent the randomized participants.
The record also does not provide a clinical threshold for interpreting the magnitude of MAP changes or a comparison with a separate untreated group. The result is best read as a descriptive account of the reported within-person blood-pressure changes under the two dietary conditions, rather than as a basis for claims about clinical benefit, harm, or the effect of changing diet outside the trial.
13. Why This Trial Matters Statistically
This trial raises a statistical question that differs from a conventional parallel-group comparison. Its main endpoint is a within-person change across two diet periods, and randomization determines the order in which each participant experiences those conditions. Recognizing that structure is essential: the primary contrast is not simply the difference between blood-pressure summaries in two independent groups.
The registry record’s sequence-specific medians make it possible to see the reported central change separately for each randomized order. That separation is relevant because an observed contrast could be affected by period or sequence, but the posted summaries do not test those possibilities. The record therefore illustrates why an endpoint definition and an analysis description are both important. Knowing that a measure is paired does not reveal whether the analysis accounted for pairing, period, or sequence.
Precision is another key issue. The record includes interval bounds but does not explain what they represent. An interval’s interpretation depends on its construction; without that information, it cannot be used confidently to assess uncertainty or statistical significance. The named interquartile range is not numerically reported, so the posted summaries do not fully describe the spread of individual changes.
The difference between enrollment and the counts attached to the endpoint also highlights the importance of reporting analysis populations and missing-data handling. The registry record does not explain why the posted group counts differ or whether the available paired measurements represent all randomized participants. Such information helps readers understand whose data contribute to an estimate and whether exclusions might affect interpretation.
Finally, the study’s stated scientific motivation reaches beyond blood pressure to possible immune mechanisms, while the primary endpoint is a blood-pressure contrast. Keeping the measured outcome distinct from the motivating hypotheses prevents overinterpretation. The registry record is informative about the stated question and descriptive results, but its limited analysis details constrain independent statistical appraisal.
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.
Several trial-specific limitations of interpretation follow from the registry information. First, although the endpoint is described as a median with interquartile range, the posted spread values are absent and the reported interval bounds are not identified. This makes it difficult to judge the distribution and precision of the primary summaries.
Second, the primary outcome is presented separately by randomized sequence, and the registry record does not report a pooled within-person estimate or an analysis comparing sequences. It therefore does not show whether the apparent differences between the two medians reflect random variation, order, period, or another feature of the data.
Third, the record reports fewer endpoint observations in each sequence group than the enrollment figure, but does not explain the discrepancy. It does not report completeness of paired measurements, reasons for missing data, exclusions, or methods used to address missingness. The resulting analysis population cannot be fully evaluated from the registry record.
Fourth, masking is listed as none, and the record does not clarify whether outcome assessors or analysts were masked. It also does not report a washout period, adherence measures, detailed monitoring schedules, or an assessment of carryover. These are pertinent details for interpreting repeated dietary periods, but their absence from the record does not prove that a particular bias occurred.
Finally, no statistical analysis is posted, and no secondary outcome results are reported. The record does not give a confidence level or method for the interval bounds, a p-value, or a detailed multiplicity plan. The available data therefore support a descriptive reading of the primary summaries, but not a full independent evaluation of the inferential analysis.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: CARDIA-Salt Sensitivity of Blood Pressure (SSBP) — NCT04258332.
- Registry record last updated 2026-07-07; status last verified 2026-06.
- Results first posted 2026-07-07.
- 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.
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18. Record Summary
The registry record describes CARDIA-Salt Sensitivity of Blood Pressure as a randomized crossover study sponsored by Vanderbilt University Medical Center. It is listed as completed, with enrollment of 281, a start date of 2021-05-17, and a primary completion date of 2025-05-17. Participants were randomized to high-salt-then-low-salt or low-salt-then-high-salt dietary sequences.
The primary endpoint is the within-person change in 24-hour ambulatory MAP, calculated as high-salt MAP minus low-salt MAP after one week on each diet. The posted medians are 4.0 mm Hg and 3.2 mm Hg for the respective sequence groups. The record reports interval bounds but does not identify their statistical meaning. It does not report a pooled estimate, a formal test, or an analysis method.
The record reports no serious adverse events and no deaths in either dietary group, alongside counts of other adverse events. It lists no analyses and posts no secondary outcome results. Details about missing data, analysis populations, interval construction, and the statistical plan are not reported in the registry record.