Associations of oral contraceptive use and dietary restraint with bone speed of sound and bone turnover in university-aged women

Abstract

The associations of oral contraceptive use and cognitive dietary restraint with bone speed of sound (SOS) and bone turnover were investigated in 100 Canadian university-aged women (18-25 years old). Dietary restraint was assessed using the Dutch Eating Behavior Questionnaire (DEBQ) and daily calcium intake (Ca++) was assessed by the rapid assessment method. Quantitative ultrasound was used to measure SOS at the tibia and radius. Bone formation was estimated from plasma osteocalcin (OC), 25-OH vitamin D, and serum bone-specific alkaline phosphatase (BAP). Bone resorption was determined from serum cross-linked N-teleopeptide of type I collagen (NTx) and plasma C-terminal telopeptide of type I collagen (CTx). Weekly physical activity energy expenditure (WAeq) was assessed using a standardized questionnaire, and height, body mass, relative body fat (%BF), and chest, waist, and hip circumferences were also measured. Participants were divided into low and moderate to high dietary restrainers (LDRs and MDRs, respectively). These groups were further sub-divided into users and non-users of oral contraceptives. All groups had similar age at menarche, body composition, WAeq, and equally low levels of Ca++ and vitamin D. Within the non-users of oral contraceptives, MDR exhibited a lower tibial SOS (p <or= 0.024) and OC (p <or= 0.009) than LDR. Moreover, amongst the LDR, the oral contraceptive users had a lower tibial SOS (p <or= 0.015) and BAP (p <or= 0.002) than non-users. These results show that bone SOS and bone turnover were influenced by oral contraceptives and cognitive dietary restraint among this population of young women independent of body composition and physical activity.