Quantitative Bone Ultrasound Measurements in Young Females 14–23 Years of Age Panagiota Klentrou, Ph.D., and Izabella A. Ludwa, M.Sc. Abstract Aim: This study examined how transaxial quantitative ultrasound (QUS) measurements differed in young females between 14 and 23 years of age and if body composition and behavioral factors, namely, oral contra- ceptive (OC) use, physical activity, and calcium intake, influenced these measurements. Methods: Participants (n ¼ 595) were classified as nonusers or users of OC. QUS measurements were performed at the distal radius and midtibia, and the bone speed of sound (SOS) was recorded for each site. Body mass index (BMI) was calculated from body mass and height. Physical activity and dietary calcium intake were assessed using standardized questionnaires. Results: Bone SOS increased significantly with increasing age (r 2 ¼ 0.28 and 0.20 for radius and tibia, respec- tively, p < 0.05) but slower after age 18. OC use was not significantly associated with the QUS measurements, yet there was a significant age-by-OC use interaction ( p < 0.05) for SOS of the tibia. For the nonusers of OC, age, BMI, and calcium intake were significant predictors of tibia SOS, explaining 24% of the variance in tibial SOS scores, whereas among the OC users, only age and BMI were significant predictors of tibial SOS, explaining 18% of the variance with no other variables entering in the model. Age was the only predictor of radius SOS in both groups. QUS scores increased steadily from 14 to 23 years of age in young females. Conclusions: OC use was associated with lower tibial SOS scores in early adulthood but not during adolescence, suggesting that OC use possibly may interfere with the bone development of the tibia. Furthermore, daily calcium intake demonstrated a positive relationship with the tibial SOS only in the nonusers of OC; however, this relationship was reversed for BMI irrespective of OC use. Introduction O steoporosis is a condition characterized by low bone mass, resulting in reduced bone strength and suscepti- bility to fractures. 1 A primary risk factor for the development of osteoporosis is failure to attain peak bone mass (PBM), which is defined as the full genetic potential for bone strength based on the maximal amount of bone mineral that can be accrued. 2,3 Although debate continues as to the age at which PBM is attained, it is suggested that it is largely achieved by the end of the second decade, with 90% of total body bone mineral content (BMC) accrued by the age of 16, 4,5 after which there is a steady decline in bone mineral density (BMD). 6 It has been recommended that behaviors promoting the devel- opment of PBM and the reduction of bone loss should be understood and applied at all ages. 7,8 With less youth par- ticipating in activities meant to enhance bone health, moni- toring bone mineral accrual from adolescence to young adulthood may be important to ensure skeletal adequacy and health later in life. The majority of controlled studies, however, used radiation- based technologies to measure BMD in relatively small pop- ulation samples or included age ranges that do not extend beyond the formative years of bone development into early adulthood. 9–12 Transaxial quantitative ultrasound (QUS) is a relatively new technology for assessment of skeletal proper- ties. QUS measures the speed of sound (SOS) along the bone, and, thus, it is not affected by bone size, allowing for better comparisons between children of different sizes. 13,14 It is an inexpensive, portable technology that does not involve radi- ation and can be used in large population samples. Using transaxial transmission, the QUS parameters are related to bone density and structure 15 but not to cortical thickness, 16 which is an added advantage when working with youth or attempting to make meaningful comparisons with adults. Previous studies have demonstrated that QUS is associated Department of Physical Education and Kinesiology, Brock University, Ontario, Canada. JOURNAL OF WOMEN’S HEALTH Volume 20, Number 5, 2011 ª Mary Ann Liebert, Inc. DOI: 10.1089=jwh.2010.2214 677