Intake of dairy products and bone ultrasound measurement in late adolescents: a nationwide cross-sectional study in Japan.

INTRODUCTION There is little evidence regarding the effects of dairy product intake on bone mineralization among late adolescents, especially in Asians. The aim of this study was to determine the association between dairy product intake and bone strength as measured by quantitative ultrasound (QUS) in a large Japanese population. METHODS Subjects were 38,719 high school students (14,996 males and 23,723 females) across 33 prefectures in Japan. Bone stiffness of the calcaneus was measured by QUS densitometry (AOS-100, Aloka). Subjects were given a self-administered questionnaire, which included questions on gender, age, height, weight, consumption of dairy products, and levels of physical activity. Intake of milk and yogurt were classified as none, 1-99, 100-199, 200-399, and>or=400 ml/day. RESULTS The proportion of subjects who consumed milk 400 ml/day or more was 21% in males and 7.3% in females, while 24% of males and 41.1% of females did not consume milk. After adjusting for physical activity, weight, gender, age, and area of residence, milk intake (R2=2.8%, p<0.0001) and yogurt intake (R2=0.1%, p<0.0001) were independently associated with the QUS measurement. Similar associations were found in males and females when a gender-stratified analysis was conducted. CONCLUSION We found a positive dose-effect relationship between milk intake and bone strength in late adolescents, to whom we recommend milk intake of 400 ml/day or more to obtain greater bone mass.