The effects of the body composition, and of exercise, dietary and sleeping habits on bone mass of young people were studied. The bone mass of 339 males and 262 females aged 18-29 years were measured by the ultrasound methods. The bone mass of those subjects who exercised more than 3 times per week was significantly higher than of those with no exercise habits at school age. The subjects who continuously exercised from elementary to junior high school had the highest bone mass. A higher frequency of eating small fish in the school-aged diet was associated with higher bone mass. The bone mass of the female subjects who went to bed later than 1 a.m. was significantly lower than of those who went to bed before 1 a.m. in junior high school, high school or the present time. Multiple linear regression analysis showed exercise in junior high school to be the factor having the highest association with bone mass, this being followed by body weight and the time of going to bed in high school.
