Self-report of 24-h urine completeness compared with <i>para</i> -aminobenzoic acid (PABA) recovery does not bias estimates of dietary salt intake in the UK

The measurement of sodium excretion in 24-h urine samples is the recommended method to assess dietary salt intake to monitor salt-related public health policies. Ensuring complete collection of 24-h urine samples is important for the accurate assessment of salt intake. We compare the use of the objective biomarker, recovery of <i>para</i>-aminobenzoic acid (PABA), to self-reported 24-h urine completeness. Data collected from 868 men and women aged 19-64 years from the England Sodium Survey 2018/2019 (part of the UK National Diet and Nutrition Survey (NDNS)) were used to compare self-reported 24-h urine completeness based on a collection duration of 23-25 h, no missed urine collections/voids and a minimum urine volume of > 0·4 L against completeness based on the urinary recovery of oral doses of PABA. Two-thirds (69 %; 561/812) of participants who adhered to the PABA protocol provided a complete 24-h urine collection. Assessed by self-report, 71 % (619/868) of participants provided a complete 24-h urine collection. Sodium excretion was (geometric mean (interquartile range)) 127 (97-170) mmol/24 h with PABA and 126 (97-169) mmol/24 h by self-report; salt intake was 7·40 (5·65-9·94) g/d and 7·38 (4·53-8·83) g/d, respectively. The proportion of participants above the UK-recommended salt intake of 6 g/d was 70 % by both PABA and self-report. This study shows that the use of self-report of 24-h urine collection completeness provides an assessment of sodium excretion and dietary salt intake with the same accuracy as when PABA recovery is used to assess completeness.