Osteoporosis is one of the most common chronic disease in Japan and the second cause of disablement from standing. It is a condition in which bone mass decreases by aging, causing bones to be more susceptible to fractures. There is no other way to cure osteoporosis than the prevention so far. Therefore, peak bone mass in young age is important and should be high as much as possible to prevent osteoporosis.
　We have measured peak bone mass in healthy young women and examined some related factors to the increase of the bone in their life styles. Forearm bone density of 76 healthy female students from 19 to 24 years old were measured by single photon absorptiometory method and their physical activities, nutritional status, past fractures and other physical conditions were observed.
　Sixteen percent of the total have low bone density as below 85% of the mean value, which is similar to the 50~60 years old. Much more students with the low bone density dislike sports than those with high bone density above 115% of the mean. Their past physical exercise in high school age had been as little as half of those with the high bone density. Calcium intake in those with the low bone density was about 380 mg / day and 63% of the RDA (600 mg / day), while those with the high bone density were almost similar to the RDA. More students with the low bone density did not drink milk in their childhood and had artificial feeding in their baby-hood.
　Thus we suggest here such risk factors of osteoporosis as physical exercise, calcium intake and milk feeding from the very young should be took into consideration and low bone mass should be improved from early stage of life in order to prevent osteoporosis in the old age.

DESCENTE SPORTS SCIENCE Vol.11/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE