Urinary biochemical markers of dietary intake in the INTERSALT study

The INTERSALT Study, an international, collaborative, cross-sectional investigation of the relation between blood pressure and dietary and other factors, used quality-controlled, standardized procedures and assessment of multiple possible confounding factors to study 10 079 men and women in 52 population-based samples in 32 countries. In this study 24-h urinary excretion data were used as biochemical markers of intakes of sodium, potassium, and protein, with repeat examinations done in a randomly selected 8% of participants to assess reliability and correct for regression-dilution bias. INTERSALT showed that high salt intake, low potassium intake, excess alcohol consumption, and energy imbalance resulting in overweight are critically involved in the origins of the high blood pressure prevalent among a majority of adult populations. The findings also show that obtaining accurate estimates of associations between dietary intake and blood pressure requires large population-based samples, high-quality dietary information, control for multiple confounding variables, and modern multivariate methods of data analyses, including correction of observed associations for within- person variation in intake.