ABSTRACT & COMMENTARY

Synopsis: Consumption of an average of 300 mL of milk each day by adolescent girls over an 18-month interventional study significantly enhanced bone

mineral acquisition.

Source: Cadogan J, et al. Milk intake and bone mineral acquisition in adolescent girls: Randomized, controlled intervention trial. BMJ 1997;315:1255-1260.
In this study, cadogan and associates recruited 82 girls from the Sheffield, England, school system. Subjects were randomized to a control group, maintained on their baseline diets, or an intervention group. The intervention group each received an extra pint of milk per day, delivered to their homes. The two groups were well-matched with respect to age, physical development, anthropomorphic measures including height, weight, lean and fat body mass, and measured bone mineral content and density at the outset. The study girls were instructed to drink as much of the provided milk as possible. After 18 months, measurements of bone mineral content and density, as well as a variety of biochemical markers of bone turnover were performed on both groups. Increases in total body bone mineral density and total body bone mineral content were significantly greater in the milk-supplemented group than in controls. Regional sites where increased bone mineral content was evident were at the pelvis and legs. Measures of bone turnover did not differ between the two groups. Thus, the increase in mineral accretion could not be attributed to an increase in bone formation or to a decrease in bone resorption.

Calcium intake in the experimental group (~1100 mg/d) was significantly greater than that of the control group (~700 mg/d). The latter value is just under the age-related reference nutrient intake for calcium in the United Kingdom. Other nutrients, including protein, magnesium, phosphorus, and zinc, were also increased by the milk supplement but to a lesser extent than calcium.

COMMENT BY WALTER R. ANYAN, Jr., MD, FAAP

We understand osteoporosis primarily as a disease of the elderly and, in particular, a major public health problem in postmenopausal women. Caucasian women account for 26 million people in the United States with high-fracture risk. Indeed, more than 350,000 hip fractures occurred in North America in 1990, resulting in burdensome expenditures.lAlthough bone turnover can be medically manipulated to some extent during these later years, a great deal of controversy exists regarding an effective, safe, and acceptable treatment for osteoporosis in elderly women. Thus, an approach to preventing osteoporosis by ensuring optimal development of the skeleton at an early age warrants attention and places this disorder into the realm of the pediatric and adolescent medicine physician. This study addresses the interesting proposition that milk supplementation can enhance the accretion of bone mineral during the adolescent years. The concept is of considerable importance since peak bone mass is established in young women by approximately 18 years of age,2and approximately 20% of peak bone mass is determined by environmental factors, particularly physical activity and mineral intake during adolescence.3Indeed, the most rapid period of accretion of bone mineral occurs in females between the ages of 11-16 years.4

This biological phenomenon may provide insight to useful measures for the attainment of an optimal peak bone mass during the dynamic window of rapid accretion. This and similar studies of dietary intervention5 should stimulate us to encourage appropriate calcium intake during the adolescent years. The consideration of the nutritional effect on development of the skeleton should begin in childhood but should not be discarded after adolescence. Although we do not yet know the effect of such intervention on the later development of osteoporosis, it makes sense that attention to skeletal nutrients should be maintained throughout life-before, during, and after adolescence, as well as in postmenopausal years. (Dr. Anyan is Professor of Pediatrics and Adolescent Medicine at the Children's Hospital at Yale-New Haven, CT.)

References

1. Wasnich RD. Epidemiology of osteoporosis. In: Favus MJ, ed.Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism. 3rd ed. Philadelphia-New York: Lippincott-Raven Publishers; 1996:249.

2. Matkovic V, et al. Timing of peak bone mass in Caucasian females and its implication for the prevention of osteoporosis. J Clin Invest 1994;93:799-808.

3. Marcus R. Physical activity and regulation of bone mass. In: Favus MJ, ed. Primer on the Metabolic Bone Diseases and Disorders of Mineral Metabolism. 3rd ed. Philadelphia-New York: Lippincott-Raven Publishers; 1996:254.

4. Zanchetta JR, et al. Bone mass in children: Normative values for the 20-year-old population. Bone 1995;16: 393S-399S.

5. Bonjour J-P, et al. Calcium-enriched foods and bone mass growth in prepubertal girls: A randomized, double-blind, placebo-controlled trial. J Clin Invest 1997;99:1287-1294.