[Comparison of dietary survey, frequency and 24 hour urinary Na methods in evaluation of salt intake in the population].

OBJECTIVE: To compare the difference and correlation between dietary salt intakes assessed by 24 hours urinary Na method, food weighted record method and food frequency questionnaire method.
METHODS: All 2 184 subjects aged 18 to 69 were selected by multi stage stratified cluster random sampling method in Shandong province in June to September, 2011. Dietary salt intakes were measured by 24 hours urinary Na method, food weighted record method and food frequency questionnaire method. The information on gender, age, dining locations and labour intensity of members dining at home for 3 days were recorded. And the dietary habits were surveyed by questionnaire.
RESULTS: Salt intakes were 14.0, 12.0 and 10.5 g/d assessed by 24 hours urinary Na method, food weighted record method and food frequency questionnaire, respectively. Comparing with 24 hours urinary Na method, salt intakes assessed by food weighted record method and food frequency questionnaire method were 2.0 g (14.3% undervalued) and 3.4 g (24.3% undervalued) less, respectively. Comparing with 24 hours urinary Na method, the proportion of individuals with salt intake over-reported and under-reported were 42.4% (856/2 020) and 55.3% (1 117/2 020) by food weighted record method, and were 20.7% (418/2 020) and 16.3% (329/2 020) by food frequency questionnaire method, respectively; the proportion of individuals with salt intakes within ± 25% of 24 hours urinary Na method were 36.9% (745/2 020) and 28.4% (574/2 020), respectively. Salt intakes assessed by 24 hours urinary method correlated significantly with both salt intakes assessed by food weighted record method and food frequency questionnaire method; the correlation coefficients were 0.13 and 0.07, respectively. With the increasing of salt intakes by subjects' self-judgment, salt intakes were all rising significantly using three survey methods. Salt intakes of three group population of light, moderate and partial taste salty were 13.6, 13.6 and 14.7 g/d by 24 hours urinary Na method (F = 0.47, P < 0.05); 11.0, 12.0 and 12.7 g/d by food weighted record method (F = 5.83, P < 0.05), and 9.3, 10.2 and 11.9 g/d by food frequency questionnaire method (F = 5.83, P < 0.05), respectively.
CONCLUSION: Comparing with 24 hours urinary method, food weighted record method and food frequency questionnaire method would undervalue dietary salt intake. Salt intake status can be more accurately assessed by adjusting the underestimation rate.