ABSTRACT

　High intensity exercise has been reported to induce increases in systemic parathyroidhormone （PTH） levels. PTH is involved in the conversion of 25-hydroxyvitamin D（25（ OH）D） to 1 alpha, 25-hydroxyvitamin D3（ 1α, 25（ OH） 2D3）; thus, 25（ OH）D levels may potentially decrease through conversion to 1α, 25（ OH） 2D3 followingexercise induced increase in PTH levels. The purpose of this study was to investigatethe influence of differences in exercise volume on 25（ OH）D levels and bone mass.Seven-week-old female C57/BL6j mice were divided into three groups: sedentary（CON, n = 5）， exercise once a day（ EX-1, n = 5）， and exercise three times a day（ EX-3, n = 5） . The exercise groups were subjected to 30 minutes of treadmill running at 12m/min on a 5° incline; animals exercised 5 days a week for 4 weeks. Following thefinal exercise session of week 4, serum PTH levels had significantly increased in theEX-3 group compared with the CON group （p < 0.05）．At the same time point, thenumber of mice where no serum 25（ OH）D could be detected were 50% in the EX-3group. Muscle wet weight was increased in the EX-3 group compared with the CONgroup （p < 0.05）．Bone mineral density （BMD） was increased in the EX-3 group compared with both the CON （p < 0.05） and EX-1 groups （p < 0.05）．This studywas suggest that increased exercise volume has the potential to decrease 25（ OH）Dlevels, although it was seen to be increased in muscle wet weight and BMD. Therefore,we conclude that athletes with intense training regimens should consume diets rich invitamin D.

DECENTE SPORTS SCIENCE Vol.40/The DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE