Bone mineralization in the first year of life in infants fed human milk, cow-milk formula, or soy-based formulaMimouni F, Campaigne B, Neylan M, et al. Journal of Pediatrics. 1993;122:348-354.

IntroductionIn several reports, soy-based infant formulas have been shown to support adequate growth in term infants,1-7 but concerns have been raised about the adequacy of bone mineralization1,8,9 Manufacturers have since improved the suspensibility of minerals in these formulas (especially calcium and phosphorus) in order to improve their delivery and absorption by the infant.

Study PurposeThis study sought to further the understanding of growth and bone mineralization patterns during the first year of life for infants fed human milk, cow milk-based infant formula, or soy protein-based infant formula.

Study DesignThe study had a single-blind, prospective design, with randomization to three formula groups. The three formula groups were compared with a concurrently recruited human milk-fed group. For ethical reasons, the human milk-fed group was self-selected by parental preference (n=10). For formula-fed groups, parents were aware of the specific formula assignment, but investigators measuring outcome variables were not. A total of 107 infants were enrolled in the study. Seventy-two infants continued in the study until at least the 16-week follow-up visit; this group of 72 infants was included in the analysis.

Study subjects were assigned to one of three groups:1) Cow milk-based formula (Similac, Abbott Nutrition) (n=20)2) Soy protein-based formula (Isomil, Abbott Nutrition) ( n=21)3) Soy protein-based formula (Prosobee, Mead Johnson) ( n=21)

Serum vitamin D levels are an index of mineral sufficiency; an elevated level may indicate compensation for insufficient mineral availability.

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Subjects were examined at baseline (2-7 days old) and at 8, 16, 26, and 52 weeks of age. Three days prior to each follow-up visit, parents completed dietary records of the amounts of formula consumed and indices of formula tolerance. Measures of growth (e.g. weight, length, head circumference), bone mineral content (BMC) and selected blood chemistry values (e.g. serum ionized and total calcium, phosphorus, magnesium, alkaline phosphatase, and 1,25-(OH)2D) were made at entry and at each follow-up visit.

Study ResultsThere were no significant differences in growth and bone mineralization during the first year of life in infants fed soy protein-based formula compared with infants fed cow milk-based formula. However, the rate of length gain was higher in formula-fed infants (all 3 groups) than in the human milk-fed group in the first 6 months of life (p <0.01), though this distinction did not persist at 1 year.

Serum phosphorus concentrations were higher in formula-fed than human milk-fed infants, but there were no differences in BMC between human milk-fed and formula-fed infants. Serum 1,25-(OH)2D levels were elevated at 8, 16, and 26 weeks (P<0.05, 0.01 and 0.01 respectively) in those infants fed Prosobee.

DiscussionThe results of this study support the theory that increased concentration and enhanced suspensibility of minerals in two commercially-available soy-based formulas appear to promote adequate growth and bone mineralization. Regardless of the mechanism for bone mineralization, it may be concluded that currently-available, soy-based formulas are an acceptable alternative for term, non-human milk-fed infants with lactose sensitivity or cow milk protein allergy and without allergy to soy.

While elevated 1,25-(OH)2D concentrations are usually perceived as a physiologic adaptation to inadequate mineral intake or high mineral need,10 the elevated level of serum vitamin D in the Prosobee group was apparently sufficient to increase calcium absorption efficiency, leading to adequate BMC.

Study ConclusionsThere appear to be no significant differences—either statistically or biologically—in growth and bone mineralization in the first year of life between infants fed cow milk-based formula and infants fed soy protein-based formula. Though the rate of length gain was higher in formula-fed infants in the first six months of life and there were some differences in blood chemistry values between the formula-fed infants and the human milk-fed infants, there were no differences in BMC.

Key Finding:

Bone mineral content is similar in term infants fed cow milk-based formula, soy protein-based formula or human milk.

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References

1. Chan GM, Leeper L, Book LS. Effects of soy formulas on mineral metabolism in term infants. Am J Dis Child. 1987;141:527-530.

2. Cherry FF, Cooper MD, Stewart RA, et al. Cow versus soy formulas. Comparative evaluation in normal infants. Am J Dis Child. 1968;115:677-692.

3. Dean ME. A study of normal infants fed a soya protein isolate formula. Med J Aust. 1973;1:1289-1293.

4. Jung AL, Carr SL. A soy protein formula and a milk-based formula. A comparative evaluation in milk-tolerant infants showed no significant nutritional differences. Clin Pediatr (Phila). 1977;16:982-985.

5. Kohler L, Meeuwisse G, Mortensson W. Food intake and growth of infants between six and twenty-six weeks of age on breast milk, cow’s milk formula, or soy formula. Acta Paediatr Scand. 1984;73:40-48.

6. Nande S, Prinsloo J, Haupt C. Comparison between a humanized cow’s milk and a soy product for premature infants. S Afr Med J. 1979;55:982-986.

7. Sellars WA, Halpern SR, Johnson RB, et al. New growth charts: soy, cow, and breast milk comparison. Ann Allergy. 1971;29:126-134.

8. Bainbridge RR, Mimouni F, Tsang RC. Bone mineral content of infants fed soy-based formula. J Pediatr. 1988;113:205-207.

9. Steichen JJ, Tsang RC. Bone mineralization and growth in term infants fed soy-based or cow milk-based formula. J Pediatr. 1987;110:687-692.

10. Rosen JF, Chesney RW. Circulating calcitriol concentrations in health and disease. J Pediatr. 1983;103:1-17.

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