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Bone Health: Studies in Children and Adolescents

A meta-analysis published in 2008 of 21 randomized controlled trials consisting of 3,821 children aged 4 to 17 years (82% of whom were female) on the role of milk products and dietary calcium on bone mineral content in children revealed a number of benefits:¹

• Among studies of children with low baseline calcium intakes, there was a significant benefit on bone mineral content with milk products or calcium supplements;
• Calcium intakes at the levels used in the relevant studies increased total bone mineral content by almost 50 g on average (49.9 g; 95% CI, 24.0-76.6) over 18 to 24 months;
• Increased dietary calcium or milk products, with and without vitamin D, significantly increased total lumbar spine bone mineral content in children with low baseline calcium intakes.

The Framingham Children’s Study, which collected dietary data over a period of 12 years from 106 children aged 3 to 5 years at baseline, assessed milk product intake on parameters of adolescent bone health at ages 15 to 17 years. Bone mineral content and bone area for total body and 6 regions (arms, trunk, ribs, pelvis and spine) were the primary outcomes:²

• Milk product intake at 13 to 17 years of age was a stronger predictor of bone health than intake at earlier ages;
• Children who consumed 2 or more servings/day of milk products had significantly better bone health outcomes (bone mineral content, bone area, bone mineral density) compared to children who consumed fewer than 2 servings/day;
• Higher intakes of meats and other proteins (4 or more servings/day) were also associated with higher mean bone mineral content and bone area;
• Children with higher intakes of both milk products and meats and other proteins had the highest mean bone mineral content and bone area values.

Children with higher intakes of both milk products and meats and other proteins had the highest mean bone mineral content and bone area values.

In a cross-sectional study published in 2009 consisting of 192 healthy adolescent girls and young women aged 12 to 22 years looked at milk product consumption and calcium intake from other food sources:³

• Milk intakes averaged 166 mL/day (range 0-525 mL/day), corresponding to a mean calcium intake of 200 mg/day from milk, which is far below the recommendations for this group;
• The calcium contribution of each food was as follows:
  • Milk = 22%
  • Cheese = 14%
  • Yogurt = 11%
  • Other milk products = 4%
  • Other non-milk products = 49%
• Milk intakes were not significantly associated with any of the studied parameters in premenarcheal girls;
• Bone mineral content, bone mineral density (g/cm²) and bone mineral density (z score) were significantly associated with milk intakes in postmenarcheal girls;
• Adolescents and young adults with milk intakes below 55 mL/day (on average 13 mL/day) had an 8% lower bone mineral content and a 7% lower bone mineral density compared to girls with milk intakes over 260 mL/day ;
• The percentage of girls with osteopenia was higher in low milk consumers (27%) and even more so in girls over 16 years (43%) than in high milk consumers (11%);
• Bone mineral content and bone mineral density in postmenarcheal girls were significantly associated with calcium, phosphates, magnesium, protein and energy from milk but not with the same nutrients provided by other dietary sources.

In a cross-sectional study of 50 milk avoiders (30 girls and 20 boys) aged 3 to 10 years, bone mineral density was assessed via dual-energy X-ray absorptiometry, and the results were compared to those of 200 milk-drinking control children:⁴

• Children who avoided milk were significantly shorter, had smaller skeletons, had a lower total body bone mineral content (p < 0.01), and had lower z scores (p < 0.05) for areal bone mineral density at the femoral neck, hip trochanter, lumbar spine, ultradistal radius, and 33% radius than children of the same age and sex and from the same community who drank milk;
• In growing children, long-term avoidance of cow milk is associated with small stature and poor bone health.

In a longitudinal study consisting of a long-term randomized controlled trial and an observational component, the impact of calcium supplements and milk product intake was evaluated in pre-pubertal children over a 7-year period.⁵

By the average age of 15 years, the dairy group remained significantly taller and had higher dietary calcium and protein intakes as compared to the calcium supplemented and placebo groups:

• The dairy group had a higher bone mineral density of the spine at age ~15 years and this was maintained up to the age of ~18 years;
• Bone mineral density of the hip in the dairy group was similar to that of the calcium supplemented group;
• The cross-sectional area of the proximal radius was much higher in the dairy group compared to the clinical trial individuals (p = 0.008);
• Overall, this study indicated that calcium and milk products influence bone mass acquisition, which leads to higher peak bone mass.

In a cross-sectional study of 649 girls from the Beijing area aged 12 to 14 years, the relationship between diet and bone mineral status was examined:⁶

• Results showed that Beijing pubertal girls had a low mean milk consumption of about 50 g/day, whereas one third consumed no milk products at all;
• Milk consumption included fresh and powdered milk, vitamin-D fortified milk, and yogurt;
• The mean calcium intake was 356 mg/day, of which only 21% was provided by milk and milk products;
• Milk intake varied by region (rural, suburban, and urban: 9 g/day, 36 g/day and 83 g/day respectively, p < 0.0005) as did the proportion of milk consumers in the three areas (30%, 64% and 91% respectively, p < 0.0005);
• Milk was the only factor included in the models for bone mineral content at the four bone sites measured;
• Milk was the only food group with significant partial correlation with bone mineral content;
• The results indicate that milk (presumably as an integrated source of nutrients) had a beneficial effect on bone mass of Beijing pubertal girls and was a better nutritional determinant of bone mineral content than intake of any milk nutrient alone.

The authors conclude that milk consumption should be encouraged in this population group for the attainment of optimal bone mass.

Ninety-one girls aged 15 to 16 years who participated in a two-year randomized controlled trial on the effects of supplemental milk product intakes on dietary patterns, body composition and bone density were recruited one year after the cessation of the study to determine the effects of terminating supplemental milk product consumption on bone mineral density, dietary habits, biochemical markers, body composition and blood lipids:⁷

• In the supplemented group, each girl selected milk products (types not specified) under the guidance of a dietitian to meet the minimal requirement of 1,000 mg calcium/day;
• The supplemented group had significantly higher calcium, phosphorus and protein intakes during the supplementation period (p < 0.001). No differences in intakes were seen between the groups 12 months after supplementation finished;
• There was a significant increase in the trochanter (4.6%), lumbar spine (1.5%) and femoral neck (4.8%) bone mineral density (p < 0.05) when subjects were supplemented with milk products at a mean calcium intake of 1,160 mg/day;
• Supplemental milk product intakes were also seen to have an effect on bone mineral content, particularly at the trochanter and to a lesser extent at the lumbar spine.

In an 18-month randomized controlled trial of 82 white girls (mean age 12 years), the impact of 568 mL of milk supplementation (whole or reduced fat) on measures of bone health was determined:⁸

• Milk intake at baseline was 150 mL per day in both groups. On average, the intervention group consumed an additional 300 mL per day throughout the trial;
• The milk group had significantly greater increases in bone mineral density (9.6% vs. 8.5%, p = 0.017) and bone mineral content (27.0% vs. 24.1%, p = 0.009) compared to the control group;
• Increased milk consumption significantly enhances bone mineral acquisition in adolescent girls and could favourably modify the attainment of peak bone mass.

Another randomized controlled trial consisting of 48 white girls (mean age 11 years) examined the impact of a diet supplemented with milk products and that provided a recommended intake of 1,200 mg of calcium/day on measures of bone health:⁹

• The milk product group (milk, cheese, yogurt) had higher intakes of calcium, phosphate, vitamin D and protein than the control group;
• During the one-year study, the milk product group had significantly greater gains in bone mineral density at the lumbar spine bones (22.8% ± 6.9% vs.12.9% ± 8.3%) and in total body bone mineral (14.2% ± 7.0% vs. 7.6% ± 6.0%) than control subjects;
• Dietary calcium, phosphate, vitamin D, and protein intakes were associated with lumbar bone density and total body bone calcium. These nutrients were provided mainly by milk products;
• Young girls whose dietary calcium was provided primarily by milk products at or above the recommended dietary allowances had an increased rate of bone mineralization.

Keywords: health studies, bone health

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