A three-year follow-up study on bone density development in Japanese peripubertal children

近几十年来，日本儿童骨折的发病率逐渐增加。对儿童骨折危险因素的调查可能会导致在以后的生活中预防骨折。为探讨生长期儿童骨折的可能原因，我们对570名健康儿童（283名男孩）进行了纵向研究，年龄从4年级（10岁或11岁）到9年级（分别为G4到G9），用DXA测量了脊柱（LS）和全髋（TH）的面骨密度（aBMD）。受试者在基线后3年被邀请进行随访调查。432名受试者（203名男孩）（75.8%）完成了调查。vBMD是在假设脊柱为圆柱体的情况下在LS处估计的。在基线时，两种性别的LS和TH处的身高和aBMD随着年龄的增长而线性增加。女孩的vBMD也有类似的增加，但男孩没有，男孩在G6（12或13岁）时vBMD最低。男孩在G6至G7期间和女孩在G4至G5期间观察到身高和aBMD的最大年变化率。然而，vBMD的年变化率在男孩的G8至G9期间和女孩的G7至G8期间最大。体重越重、牛奶摄入量越多、体力活动量越多的人，其BMD变化率越大，vBMD最低值出现在身高增长速度最快的年龄，也就是男女骨折发生率最高的年龄。与身高增长相比，骨密度获得延迟可能导致骨密度降低，这可能导致生长期儿童骨折的短暂增加，并且可以通过改善本研究中发现的生活方式因素来预防。

Incidence of fracture in Japanese children has increased progressively in these decades. Investigations into risk factors for children's fracture may lead to prevention of fractures later in life. We examined possible causes of fractures in growing children by estimating volumetric bone mineral density (vBMD) in a longitudinal study.We examined healthy 570 children (283 boys) from 4th (10 or 11 years) to 9th grade of a compulsory school (G4 to G9, respectively) for whom areal BMD (aBMD) at the spine (LS) and total hip (TH) were measured by DXA. The subjects were invited for a follow-up survey 3 years after the baseline. 432 subjects (203 boys) (75.8%) completed the surveys. vBMD was estimated at LS under an assumption of the spine being a cylinder.Height and aBMD at LS and TH at baseline increased linearly with advancing in age in both genders. Similar increase was observed in vBMD in girls but not in boys, who showed the lowest vBMD in G6 (12 or 13 years). The greatest annual rate of changes in height and aBMD were observed during G6 to G7 in boys and G4 to G5 in girls. However, the annual rate of change in vBMD was the greatest during G8 to G9 in boys and during G7 to G8 in girls. The rates of change in BMDs were greater in those who had heavier weight, greater intake of milk and greater physical activities.The lowest vBMD was observed at the age of peak velocity of height growth which is the age at the highest fracture incidence in both genders. Delay in gaining bone density compared with height growth may cause low bone density, which may result in the transient increase in fractures in growing children, and may be prevented to improve the lifestyle factors found in this study.