Effect of calcium supplementation on blood pressure in children.

OBJECTIVE: To evaluate the effect of calcium supplementation on blood pressure in children. DESIGN: Randomized, double-masked, placebo-controlled trial. SETTING AND PARTICIPANTS: One hundred one fifth-grade students in one inner-city school. INTERVENTION: Each child consumed 480 ml of juice beverages, containing either no calcium or 600 mg calcium (as calcium citrate malate) daily for 12 weeks. MEASUREMENTS: At baseline we obtained nutrient data from three sets of 2-day food records on each subject. We measured blood pressure four times on each of three weekly sittings at baseline and at follow-up. Using multiple linear regression analysis, we compared mean blood pressure change in the intervention group with that in the placebo group. RESULTS: There were 50 girls and 51 boys; 61 subjects were black. At baseline, mean age was 11.0 years, systolic and diastolic blood pressures were 101.7 and 57.7 mm Hg, daily total energy intake was 1966 kcal, and calcium intake was 827 mg. With control for age, height, hours of television watched, and baseline blood pressure, systolic blood pressure increased 1.0 mm Hg in the intervention group and 2.8 mm Hg in the placebo group (effect estimate = -1.8 mm Hg; 95% confidence interval -4.0, 0.3). In black subjects the intervention effect estimate was -2.0 mm Hg (95% confidence interval -4.4, 0.4). From lowest to highest quartile of baseline calcium intake (per 1000 kcal), the intervention effect estimates were -3.5, -2.8, -1.3, and 0.0 mm Hg (p for trend = 0.009). There was little effect on diastolic blood pressure. CONCLUSION: These data suggest a blood pressure-lowering effect of calcium supplementation in children, especially in subjects with low baseline calcium intake.

Identifying children at high risk for the development of essential hypertension.

BACKGROUND AND OBJECTIVES: Because blood pressure (BP) tracks from childhood to adulthood, some have recommended screening to identify children at high risk for the development of essential hypertension as adults. Others, however, have argued against this strategy because they believe that correlations between childhood and adulthood BP levels are too low. To address these issues, we considered prediction of adult BP from childhood levels. DESIGN: Cohort study with follow-up of participants from childhood to early adulthood. SETTING AND PARTICIPANTS: We ascertained BP in 337 schoolchildren from East Boston, Mass., and reexamined 317 (94%) of them 8 to 12 years later, at ages 18 to 26 years. MEASUREMENTS AND DATA ANALYSIS: On each of several visits, 1 week apart (four for children, three for adults), we obtained three BP readings with a random-zero sphygmomanometer. To calculate correlation coefficients (tracking correlations) between childhood and adult BP, we assumed a multivariate normal distribution and used an iterative maximal likelihood approach in a longitudinal model. We then used these correlations in expressions for sensitivity and specificity of childhood BP as a screening test and for positive predictive value for adult BP above specified cutoff points. RESULTS: During the 8- to 12-year interval, tracking correlations, corrected for within-person variability and adjusted for age, sex, smoking, and medication and alcohol use, were 0.55 for systolic BP and 0.44 for diastolic BP. The corresponding positive predictive values indicated that, for example, the probability that a 20-year-old man's true systolic BP will be > 139 mm Hg (> 90th percentile) was 0.44, given that his observed average systolic BP at age 10 years was > 95th percentile (> 117 mm Hg). The sensitivity of a 10-year old boy's systolic BP > 95th percentile to detect systolic BP > 139 mm Hg 10 years later was 0.17. The specificity of his BP < 95th percentile at age 10 years to detect systolic BP < 139 mm Hg at age 20 years was 0.97. For diastolic BP, predictive values and sensitivities were somewhat lower. CONCLUSIONS: After correction for within-person variability, tracking correlations from childhood to early adulthood are higher than previously reported. However, the resulting sensitivities and predictive values for childhood BP as a screening test for adult BP are of only modest magnitude. These data call into question the usefulness of routine BP measurement to identify children at high risk for the development of essential hypertension.

Impact of within-person variability on identifying children with hypercholesterolemia: Framingham Children's Study.

BACKGROUND AND OBJECTIVE: The National Cholesterol Education Program guidelines recommending that children be screened to detect abnormal levels of blood lipids depend on accurate assignment to risk categories. Our objective was to assess the impact of within-person variability of blood lipids on such risk classification. DESIGN AND SUBJECTS: We measured total cholesterol (TC) and high-density lipoprotein-cholesterol (HDL-C) at three successive weekly visits in 24 children aged 6 to 9 years. MAIN OUTCOME MEASURES: Using within-person variance estimates, we constructed 95% confidence intervals to evaluate how well one, two, and three lipid measurements per child allowed assignment of risk as recommended by the National Cholesterol Education Program. RESULTS: The mean, overall, and within-person standard deviations were 145.7, 24.5, and 9.2 mg/dl, respectively, for TC, and 42.8, 10.1, and 4.6 mg/dl, respectively, for HDL-C. One TC measurement allowed confident assignment to the "acceptable" (less than 170 mg/dl) category only if less than 154.9 mg/dl, and to the "high" (greater than or equal to 200 mg/dl) category only if greater than 215.1 mg/dl. The average of two TC values allowed assignment to these categories if less than 159.3 or greater than 210.7 mg/dl, respectively. For the average of three TC values, these ranges were less than 161.3 and greater than 208.7 mg/dl, respectively. With one TC measurement, no value allowed assignment to the "borderline" (170 to 199 mg/dl) category. The average of two TC values allowed assignment to the "borderline" category if between 180.7 and 189.3 mg/dl. Using the average of three values enlarged this range by 4 mg/dl. For HDL-C, multiple measurements improved risk assignment in a similar fashion. CONCLUSION: The magnitude of within-person variability of TC and HDL-C limits the ability to classify children into risk categories recommended by the National Cholesterol Education Program.