Reference data of forearm bone mineral density in healthy Japanese male and female subjects in the second decade based on calendar age and puberty onset: Japanese Population Based Osteoporosis (JPOS) study

Osteoporosis is a major public health problem in Japan. The second decade i s an important period in which to attain a high peak bone mass. However, no rmal values of forearm bone mineral density (BMD) are not well known in chi ldren and adolescents. BMD at one-third of forearm length proximal to the u lnar end plate (BMD1/3) and the ultradistal forearm (BMDud) was measured us ing dual-energy X-ray absorptiometry (DXA) in 1207 (631 males, 576 females) Japanese subjects aged 9-18 years. Puberty onset was assessed by questionn aire, by obtaining the time that pubic hair appeared in males and the time that menstruation started in females. BMD1/3 and BMDud increased steadily w ith age in males. In relation to puberty development, these parameters also increased after puberty onset although the increase in BMD1/3 was not stat istically significant after the fifth year from puberty onset and that of B MDud was not significant after the sixth year from puberty onset. BMD1/3 an d BMDud increased with age and then plateaued in females. The increase in B MD1/3 was not statistically significant after 15-16 years of age and that o f BMDud was not significant after 13-14 years of age. In relation to pubert y development, the increase in BMD1/3 leveled out after the fourth year fro m puberty onset and that of BMDud also plateaued after the third year from puberty onset. We provide reference values of forearm BMD in Japanese child ren and adolescents by DXA according to calendar age and puberty developmen t. Peak bone mass of the forearm may be in the late second decade in Japane se females.