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David A. Hanley, MD, FRCPC
Department of Medicine
Division of Endocrinology and Metabolism
University of Calgary
Calgary, Alberta, Canada T2N 1N4
To the Editor.—
The review by Lanou et al, "Calcium, Dairy Products, and Bone Health in Children and Young Adults: A Reevaluation of the Evidence,"1 is not really correct in concluding that "available evidence does not support nutrition guidelines focused specifically on increasing milk or other dairy-product intake for promoting child and adolescent bone mineralization." Leaving aside the fact that actual mineralization of bone tissue is really only assessed by bone biopsy, in reality, randomized, controlled trials of increased intakes of dairy products among children do show statistically significant improvements in measurements of bone mineral content.2–7 The authors have made an error that is commonly seen in review articles, which is to confuse "no evidence of an effect" with "evidence of no effect."8 A more reasonable conclusion of this review would be that the evidence is positive but only a small number of studies were reviewed.
Of the 37 studies cited in this review, only 23 were prospective studies, and of these 23 prospective studies, only 3 evaluated the efficacy of dairy products as the calcium source in promoting bone mineral content.2,3,9 Of these 3 studies, the 2 randomized, controlled trials found significantly superior increments of bone mineral measurements among those receiving increased dairy products compared with those who were not on increased dairy products.2,3 The third study was a cohort study that assessed the association between existing dairy calcium intakes and the change in bone mineral density over the next year among 65 children and adolescents aged 7 to 20 years in Finland.9 The authors comment that the calcium intakes from dairy products were uniformly high, with only 6 subjects consuming <800 mg/day from dairy products. The lack of low calcium intakes may have precluded the finding of an association in this study between dairy calcium intakes and the change in bone mineral density. In addition, 4 recent randomized, controlled studies, which were not included in the review, also found a positive effect of dairy products on bone in children and teenagers.4–7
An additional concern with the review by Lanou et al is that none of the prospective studies considered by the authors addressed their primary research question, which was: "Is there sufficient evidence to suggest that milk and other dairy products are better for promoting bone integrity than other calcium-containing food sources or calcium-containing supplements?" None of the cited studies compared milk and other dairy products to other calcium-containing food sources or calcium-containing supplements. Rather, the trials of milk intake used no intervention in their control groups. In the process of conducting a careful and systematic review, the authors should have excluded all studies that did not match their research question.8
It is important to clarify for the readers of Pediatrics that randomized, controlled trials of increased dairy-product intakes among children and teens have consistently shown statistically significant improvements in bone mineral content.2–7 The studies have been of limited duration, and therefore it remains to be established whether these improvements in bone are sustained through to young adulthood or can help prevent the development of osteoporosis in later life.
REFERENCES
Related articles in Pediatrics:
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