COMPARISON OF SERUM-CALCIUM LEVELS BETWEEN JUNIOR-HIGH-SCHOOL CHILDREN WITH HIGH-NORMAL AND LOW-NORMAL BLOOD-PRESSURE - THE CHILD AND ADOLESCENT BLOOD-PRESSURE PROGRAM

The objective of this study was to compare serum calcium levels, dieta ry calcium intake, and urinary calcium excretion between junior high s tudents with high-normal and low-normal blood pressure. The study was conducted in 11- to 14-year-old children recruited after blood pressur e screening of 5th to 8th grade Minneapolis and St. Paul Public School students. Comparisons were made between a group of 243 children selec ted from the upper 15 percentiles of the blood pressure distribution ( high-normal group) and 40 children randomly selected from the lowest 1 0% of the blood pressure distribution (low-normal group). Blood sample s were obtained from the participants at clinic visits conducted after school. Calcium measurements were based on the principle that serum c alcium is found in three forms: 1) an ionized fraction; 2) a fraction complexed with organic anions such as citrate, phosphate, and lactate; and 3) a protein-bound fraction. Dietary calcium intake was determine d from food diaries, and urinary electrolytes were determined in 24-h urine collections. Serum total calcium levels were not significantly d ifferent between groups. However, serum ultrafilterable, true ionized, ionized normalized for pH, and complexed calcium levels were signific antly greater in the low-normal group. There was no significant differ ence in 24-h intake of calcium or other nutrients between the groups. The low-normal group excreted significantly more calcium than the high -normal group, but there were no significant differences in sodium, po tassium, or chloride excretion. This report of the relation between ca lcium and blood pressure represents the first study in children or ado lescents to include serum, dietary, and urine data. The results sugges t that calcium metabolism may differ between individuals with low- and high-normal blood pressure during the first two decades of life and p rior to the onset of essential hypertension.