Key Points
- Review the observational evidence associating dietary salt intake with blood pressure and examine the methodological difficulties and biases impacting study interpretation.
- Reviewed published across-population and within-population observational studies assessing sodium intake and blood pressure, excluding the INTERSALT study.
- Evaluated methodological limitations, specifically ecological confounding in across-population literature and regression-dilution bias stemming from day-to-day intake variation in within-population studies.
- Analyzed an overview of observational studies that quantified sodium intake via 24-hour urinary excretion.
- Across-population studies showed positive associations but were limited by unstandardized field methods and ecological confounding.
- Within-population studies typically lacked statistical power and were subject to substantial regression-dilution bias that obscured true correlations.
- Studies utilizing 24-hour urinary excretion demonstrated positive and highly significant correlations between sodium intake and both systolic and diastolic blood pressure in men and women.
Structured PICO
Does salt intake correlate with blood pressure in observational studies?
PPopulationPopulations in observational studies relating salt and blood pressure (excluding INTERSALT)
IInterventionSalt/sodium intake
CComparatorLower salt/sodium intake
OOutcomeBlood pressure (systolic and diastolic)surrogate
Despite methodological limitations, observational studies using 24-hour urine excretion demonstrate a significant positive correlation between sodium intake and blood pressure.
Limitations
- Methodological difficulties and biases
- Unstandardized field methods
- Unmeasured (ecological) confounding in across-population studies
- Lack of statistical power in within-population studies
- Major regression-dilution bias due to day-to-day variation in sodium intake