Obesity, sodium intake, and blood pressure in adolescents.

Abstract

SUMMARY 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 hare 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 dlastolic (K B ) T HE existence of an association between obesity and hypertension has been known for many years. 1 Even within the normotensive range of blood pressure (BP), a positive association has been demonstrated between body weight and other measures of obesity and BP, both in adults 2 and children.8 As a potential mechanism for this relationship, an increased dietary sodium intake associated with greater food intake by obese individuals has been postulated. 4 We have studied body weight and more direct measures of obesity, sodium excretion and BP in "normal" post-pubertal adolescents, with special reference to the potential role of sodium intake as a mechanism for the relationship between obesity and BP. MethodsMembers of the Boston cohort of the Collaborative Perinatal Study 8 were invited for a heart disease risk factor evaluation at an outpatient clinic. Letters were mailed to all members of the cohort born between 1959 and 1962 with the following exceptions: letters were not sent to blacks because of their very small number in the original cohort; letters were also not sent to members of the cohort who had died, had congenital anomalies, or had not returned for a physical examination and BP measurement at 7 years of age. Of approximately 900 persons who were sent and presumably received letters (i.e., not returned by the post office), 380 responded; of these, 254 who were between 16.0 and 17.9 years of age at the time of their clinic visit make up the subjects for this study.All subjects were asked to collect overnight urine specimens on the two mornings before and the morning of their visit "to aid in the heart evaluation," and to record the times of each urine collection period. Each collection was considered complete if the urinary creatinine excretion was at least 0.4 mg/kg/hr for males and at least 0.3 mg/kg/hr for females. The 248 subjects (130 males and 118 females) included in the present analyses had at least one complete overnight collection. Three complete collections were furnished by 207 subjects (84%), two by 30 (12%), and one complete collection by 11 (4%). When more than one complete collection was available, the average of the two or three values was used.At the clinic, measurements were made of height, weight, triceps skinfold thickness, and BP...

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