Dietary sodium estimation methods: accuracy and limitations of old and new methods in individuals at high cardiovascular risk.

Objective Accurate and easy to use methods for dietary sodium (Na) intake estimation in population level are lacking. We aimed at (i) estimating the mean Na intake in the group level using a variety of dietary methods (DMs) and urinary methods (UMs) and correlating them with 24h urine collection (24UCol); (ii) improving the accuracy of the existing DMs. Design The most common DMs [three 24h dietary recalls (24DR) and food frequency questionnaire (FFQ)] and UMs [24UCol and spot urine collection using common equations] were applied. To improve the existing: (i) 24DR, discretionary Na was quantified using salt-related questions or adding extra 15% in total Na intake; (ii) FFQ, food items rich in Na and salt-related questions were added in the standard questionnaire (NaFFQ). Setting University Hospital. Participants 122 high cardiovascular risk subjects (56.0±12.6 years; 55.7% males). Results Mean 24h Na excretion (24UNa) was 2810±1304 mg/day. Spot urine methods overestimated the 24UNa (bias range:-1781 to -492 mg) and were moderately correlated to 24UCol (r=0.469-0.596, p≤0.01). DMs underestimated the 24UNa (bias range: 877 to 1212mg) and were weakly correlated with 24UCol. The improved DMs underestimated the 24UNa (bias range: 877 to 923mg). The NaFFQ presented the smallest bias (-290±1336mg) and the strongest correlation with 24UCol (r=0.497, p≤0.01), but wide limits of agreement in Bland-Altman plots (-2909mg; 2329mg), like all the other methods did. Conclusions The existing methods exhibit poor accuracy. Further improvement of the newly developed NaFFQ could be promising for more accurate estimation of mean dietary Na intake in epidemiological studies. Additional validation studies are needed.