Obesity, sodium intake, and blood pressure in adolescents.

It has been postulated that increased dietary sodium associated with greater food intake by obese people is a mechanism for the relationship between obesity and blood pressure (BP). We have evaluated this hypothesis by exploring the interrelationships of measures of obesity, sodium intake, and BP in 248 "normal" adolescents, 16 to 17 years of age. As an index of sodium intake, the sodium excretion in three overnight urine collections was used. As a more specific index of saltiness of diet, we used a ratio of sodium excretion to calorie intake, with calories estimated from 3-day diet records and dietary interview. Body weight and other measures of obesity showed a positive relationship with systolic blood pressure (SBP), but not with diastolic (K5) blood pressure (DBP5). Measures of overnight sodium excretion were positively correlated with body weight and calculated body fat percentage, suggesting that heavier people indeed ingest more sodium. This may result not from increased intake of food per se, but from increased saltiness of diet, since calorie intake did not increase with body weight. No significant relationships were found between BP and concurrent measures of sodium excretion or diet saltiness.