Meyer H et al investigated the validity of spot urine measures in the Norwegian based Tromsø study. They collected 24-hour urine and spot urine samples from 475 men and women who participated in the population-based study between 2015 and 2016, comparing 24-hour urine measures with spot-urine using three different equations (INTERSALT (with potassium), Toft and Tanaka).
From the 24-hour urine samples they found a mean sodium intake of 4.09g/day for men and 2.98g/day for women (10.4 and 7.6g of salt, respectively). The INTERSALT equation provided the closest estimate of sodium intake at 4.29g/day (difference +0.20g/day) and 2.96g/day (difference -0.02g/day) for men and women respectively.
Authors concluded that the INTERSALT equation could be used for a reasonable estimate of salt intake in this population.