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The World Hypertension League Science of Salt health outcomes review series highlights high-quality publications relating to salt intake and health outcomes. This review uses a standardised method, outlined in previous reviews and based on methods developed by WHO, to identify and critically appraise published articles on dietary salt intake and health outcomes. We identified 41 articles published between September 2019 to December 2020. Amongst these, two studies met the pre-specified methodological quality criteria for critical appraisal. They were prospective cohort studies and examined physical performance and composite renal outcomes as health outcomes. Both found an association between increased/higher sodium intake and poorer health outcomes. Few studies meet criteria for high-quality methods. This review adds further evidence that dietary salt reduction has health benefits and strengthens evidence relating to health outcomes other than blood pressure and cardiovascular disease. We observe that most studies on dietary sodium do not have adequate methodology to reliably assess sodium intake and its association with health outcomes.

Recommended standards for assessing blood pressure in human research where blood pressure or hypertension is a major focus

Although 24-h urine collection is widely considered the 'gold standard' for estimation of population sodium intake, spot urine collection is increasingly used as a convenient and affordable alternative. We used four published formulae to convert spot urine sodium into estimates of 24-h sodium excretion in order to establish which (if any) formula would be suitable for use in the New Zealand population. A convenience sample of 101 healthy volunteers provided two spot urine samples and a 24-h urine collection. Two formulae (one proposed by the Pan American Health Organisation (PAHO) and one derived from INTERSALT data) were most accurate, and provided estimates of key population indicators (mean, range and proportion above nutrient reference values) that were close to those of the measured 24-h urine excretion. Estimates using these formula were in closer agreement with 24-h excretion than the other formulae estimates using the Bland-Altman method. We conclude that spot urine sampling is a suitable alternative to 24-h urine collection in population surveys when spot urine sodium results are converted into estimates of 24-h sodium excretion using either the PAHO or INTERSALT formulae. However spot urine is a poor predictor of 24-h urinary sodium excretion for individual assessment.