Reply to T Okada

Department of Medical and Surgical Sciences
University of Otago
PO Box 913
Dunedin
New Zealand
E-mail: ailsa.goulding{at}stonebow.otago.ac.nz
Department of Human Nutrition
University of Otago
PO Box 56
Dunedin
New Zealand

Dear Sir:

We thank Okada for his interest in our earlier study that showed that 50 children who had a prolonged history of avoiding cow milk and who made no compensatory dietary adjustments for this habit were shorter and heavier than were milk-drinking control subjects of similar age and sex (1). We were intrigued to hear that he and his colleagues have also obtained evidence linking milk consumption with stature in youngsters (2). Their longitudinal study of 92 Japanese children aged 9 y showed that those who consumed high amounts of cow milk (>500 mL/d) gained 2.5 cm more height over 3 y than did those who consumed less milk (<500 mL/d), although increases in body weight did not differ significantly. Most of the children in their study consumed much higher amounts of milk than did the subjects we studied. The difference in height gain that Okada describes could reflect better general nutrition or be due to increased protein intakes and increases in insulin-like growth factor I associated with increased milk consumption (3). Alternatively, it could reflect specific anabolic responses of bone cells to cytokines and growth factors present in cow milk (4). Milk is rightly regarded as an important food for supporting pediatric growth because it is rich in many nutrients (4). The view that regular milk consumption is associated with greater height in childhood and adolescence has a long history, which dates back to the work of Leighton and Clark in Scotland (5).

We would also like to point out that the low dietary calcium intakes, reduced stature, small skeletons, and increased adiposity of our sample of milk-avoiding children (1) are not transient phenomena. These problems persist. We conducted a 2-y follow-up study of 46 of the children seen at baseline. We found that although the milk and calcium intakes of the children had increased, they were still undesirably low. These children, who are fracture-prone (6), still showed low bone mineral density. We noted that at follow-up, their z scores for height also remained significantly below those of the reference population, whereas their z scores for body mass index remained elevated. Such observations suggest that links between milk consumption and both height and bone development merit further study.

REFERENCES

1. Black RE, Williams SM, Jones IE, Goulding A. Children who avoid drinking cow milk have low dietary calcium intakes and poor bone health. Am J Clin Nutr 2002;76:675–80.
2. Iwata F, Sata Y, Hara M, et al. A study on the effect of milk intake on change of coronary risk factors. J Child Health 2000;59:608–11 (in Japanese).
3. Cadogan J, Eastell R, Jones N, Barker ME. Milk intake and bone mineral acquisition in adolescent girls: randomised, controlled intervention trial. BMJ 1997;315:1255–60.
4. Goulding A. Milk components and bone health. Aust J Dairy Technol 2003;58:73–8.
5. Leighton G, Clark ML. Milk consumption and the growth of school-children; second preliminary report on tests to Scottish Board of Health. Lancet 1929;1:40–3.
6. Goulding A, Rockell JE, Black RE, Grant AM, Jones IE, Williams SM. Children who avoid drinking cow's milk are at increased risk for prepubertal bone fractures. J Am Diet Assoc 2004;104:250–3.