Average milk and mineral intakes (calcium, phosphorus, sodium and potassium) of infants in the United States from 1954 to 1968; implications for estimating annual intakes of radionuclides.

Abstract

Dietary intake is one of the parameters needed to test metabolic models relating radionuclide burdens to environmental contamination fevels. With respect to 90Sr, the tissues of greatest potential hazard are the infant skeleton and marrow, yet the dietary intake of 90Sr by infants is less well characterized than that for any other population segment. Pertinent information from balance studies conducted in this and other laboratories, dietary surveys, and previously unavailable market research data was collected and summarized. The results were used to estimate the daily volume ±S.D. of milk products consumed by the average U.S. infant month by month from birth through the second year. Milk intake increases rapidIy from about 350 ml/day at birth to a maximum of about 840 ml/day at the end of the second month. This intake level is maintained through the sixth month, at which time nearly all infants are receiving some solid food. A decline then begins: by the tenth month milk consumption has fallen to 670 ml/day, and by 2 yr, to 530 ml/day. Milk intake varies because of differences in appetite, growth rate, body size, and solid food consumption-between-child variation–and because of fluctuations in the daily intake of each infant–within-child variation. The standard deviation (between-child variation) of the ayerage daily milk intake is about 25% for a large infant population, when measurements are averaged over enough days to eliminate daily within-child fluctuations. Market research data defined the age trends and chronological trends in the kinds of miik fed to infants–human milk, ready-to-use low-mineral formula, evaporated milk, or whole cow's milk. Average total mineral derived from milk was estimated for the average U.S. infant month by month from birth through 2 yr from (a) the daily milk intakes estimated above, (b) the fraction of infants drinking each kind of milk at each month of age, and (c) the published mineral concentrations in each kind of milk. During the first year the average daily mineral intake in milk of a large U.S. infant population was calculated to be 826 mg calcium, 660 mg phosphorus, 386 mg sodium, and 948 mg potassium. The average amounts of solid foods eaten month by month were estimated; by 6 months of age the average infant in a large U.S. population is consuming 129 mg/day of solid food, and this rises to 554 g/day by 18 months. The average mineral intake in solid foods was calculated; by 6 months of age solid foods contribute daily 104 mg calcium, 17.5 mg phosphorus, 403 mg sodium, and 391 mg potassium. A sample calculation of 90Sr intake is presented for a cohort of infants born in the vicinity of New York City on 1 January 1965; it is based on (a) the calcium intakes in each kind of milk and food month by month through 2 yr of age as developed in this paper, and (b) the published 90Sr analyses of these milks and baby foods purchased in New York city in 1965 and 1966. During the first year of life the average infant in a large U.S. population takes in 320 g calcium: 30.3 g in solid foods, 4.9 g in breast milk, 45.9 g in prepared formulas, 21.6 g in evaporated milk, and 216.3 g in whole cow's milk. During the second year total calcium intake is estimated to be 328 g: 260.4 g derived from whole cow's milk and 7.6 g from solid foods. 90Sr intakes for this cohort were estimated to be 6651 ± 1682 pCi during the first year (1965), with all but 813 pCi contributed by milks, and 5059 ± 718 pCi during the second year (1966). Estimates of both the total calcium and the total 90Sr intakes of this average group were lower than previous estimates based on different dietary assumptions.