Effects of dairy food supplements on bone mineral density in teenage girls

Background Bone mineral density (BMD) is largely genetically determined and this influence is most powerful in the period of rapid skeletal developmen t in childhood and late adolescence but environmental factors such as exerc ise and dietary calcium intake may influence up to 20%. Aims of the Study The aims of the study were to examine healthy late adoles cent females for the effects and benefits of a high calcium intake from dai ry product foods on bone mineral density, body composition, lipids and bioc hemistry. The secondary aim is determine whether a high intake of dairy pro duct foods in the diet is acceptable for this age group long term. Methods Ninety-one teenage girls who participated in a two-year randomised controlled study on the effect of dairy food supplementation on dietary pat terns, body composition and bone density in post-pubertal teenage girls wer e approached one year after the cessation of the study to determine the eff ects of the cessation of dairy supplements on bone mineral density, dietary habits, biochemical markers, body composition and blood lipids. Bone miner al density and bone mineral content were assessed at the hip, spine and tot al body. Anthropometric data were collected, and exercise, Tanner, dietary assessment, preference and compliance questionnaires were administered. Lip id profiles, hydroxyproline excretion and urinary calcium and sodium excret ion measurements were performed. Results There were no significant differences between the 2 groups for heig ht, weight, lean and fat mass. The supplemented group had significantly higher calcium, phosphorus and pro tein intake during the supplementation period (p < 0.001). No differences w ere seen between the groups 12 months after supplementation finished. There were no significant differences in exercise level, preference or acce ptability of dairy products or in the lipids and bone markers between basel ine the end of supplementation and 1 year follow-up. There was a significant increase in trochanter (4.6 %), lumbar spine (1.5 % ) and femoral neck (4.8 %) BMD (p < 0.05) in the high calcium group at the end of supplementation. There was an increase in bone mineral content at th e trochanter (p < 0.05) and lumbar spine; however the latter was not statis tically significant, in the high calcium group at the end of supplementatio n. There was no difference in vertebral height or width at any stage of the study, indicating no influence on bone size. Conclusions In this 3 year study (2 years of supplementation, 1 year follow -up), teenage girls, aged 15-18 years, were able to significantly increase their BMD at the trochanter, femoral neck and lumbar spine when supplemente d with dairy product foods to a mean calcium intake of 1160 mg/d. There was also an effect seen on the BMC particularly at the trochanter and to a les ser extent at the lumbar spine. The dietary calcium intake achieved did not adversely affect body weight, fat and lean mass or blood lipid profiles. T welve months after the supplementation finished the girls had returned to t heir baseline diet, indicating self-selection of a high dairy product diet may be hard to achieve.