Nutrición e hipertensión arterial

Design of a Nutritional Survey to Detect High Dietary Salt Intakes and Its Usefulness in Primary Care Compared to 24-Hour Urine Sodium Determination

Many population studies report salt intakes that exceed the WHO recommendation (2 g/day of Na+ or 5 g/day of salt). We do not have tools for detecting high salt intakes that are easy to apply in primary health care (PHC). We propose the development of a survey to screen for high salt intake in PHC patients. A cross-sectional study of 176 patients determines the responsible foods, and a study of 61 patients studies the optimal cut-off point and discriminant ability (ROC curve). We assessed the salt intake using a food frequency questionnaire and a 24 h dietary recall and used a factor analysis to identify the foods with the highest contribution to be included in a high intake screening questionnaire. We used 24 h urinary sodium as a gold standard. We identified 38 foods and 14 factors representing a high intake, explaining a significant proportion of the total variance (50.3%). Significant correlations (r > 0.4) were obtained between nutritional survey scores and urinary sodium excretion, allowing us to detect patients who exceed salt intake recommendations. For sodium excretion ≥ 2.4 g/day, the survey has a sensitivity of 91.4%, a specificity of 96.2% and an area under the curve of 0.94. For a prevalence of high consumption of 57.4%, the positive predictive value (PPV) was 96.9% and the negative predictive value (NPV) was 89.2%. We developed a screening survey for subjects with a high probability of high salt intake in primary health care, which could contribute to the reduction in diseases associated with this consumption.

[Correlations between dietary salt intake and 24-h urine sodium excretion in a sample of the urban population of Cáceres]

OBJECTIVE

Excessive salt intake is associated with higher levels of AHT and prevalence of cardiovascular diseases. WHO recommends consuming less than 5 g/day of salt (equivalent to 2 g Na⁺/day). Identifying foods and behaviours with greater contribution to excess intake would facilitate preventive dietary advice.

DESIGN

Observational study. SITE: Urban Health Center in Cáceres.

MAIN MEASUREMENTS

We estimated salt consumption using two food consumption frequency (FFQ) questionnaires, one generic and one with high Na+ content, and a 24 h follow-up survey. We use the Evalfinut program for nutritional evaluation of the diet. We analyzed correlations between estimated salt intake and 24-h urine sodium elimination (gold standard).

RESULTS

92% of the population had consumption higher than the recommendations with intakes equivalent to 9.5 g/day of salt (3.7 g/d of Na⁺). When sodium intake is determined by the Na⁺/K⁺ ratio, 79.54% have high intakes. Sodium elimination follows a slightly increasing trend with BMI. The perception of salt consumption is low, 56.3% consider it "adequate". 32.4% add salt to food once served. FFQ underestimate Na⁺ intake and targeted surveys provide higher values. The correlation between FFQ and Na⁺ urinary elimination is weak.

CONCLUSION

We must reduce salt intake by increasing the perception of consumption, improving knowledge about the salt content in food and identifying target patients of the health council.

Validez y limitaciones de los métodos para medir la ingesta y la eliminación de sal

La hipertensión arterial (HTA) es el principal factor de riesgo cardiovascular modificable. La HTA se puede relacionar con el consumo elevado de sal. Para medir la ingesta no todas las encuestas de alimentación son comparables y válidas. El procedimiento de referencia para valorar la ingesta de sal consiste en medir la excreción urinaria de sodio en orina recolectada durante 24 h, aunque se han propuesto métodos alternativos, como las recolecciones de muestras de orina puntuales y cronometradas. En esta revisión analizamos qué instrumentos permiten valorar la ingesta de sal y cuáles de ellos han aportado una mayor validez y fiabilidad a través de los estudios de concordancia con la eliminación de sodio en orina. Las encuestas actuales de consumo de alimentos son inadecuados debido a su amplia variabilidad y relativamente baja correlación con la eliminación de sodio en orina de 24 h. Su principal limitación es la necesidad de validación en diferentes grupos poblacionales. En Atención Primaria se debería valorar la ingesta de sal mediante la utilización de cuestionarios de frecuencia de consumo que recojan alimentos con elevado contenido en sal, el consumo de platos preelaborados y preguntas que cuantifiquen la adición de sal en la preparación de alimentos o en la mesa. Para la validación de estos cuestionarios debe emplearse como gold standard la eliminación de sodio en orina de 24 h ajustada según el aclaramiento de creatinina.