Abstracts Earth and Environmental Sciences

A longitudinal perspective of oral contraceptive use on bone mineral content in adolescents and young adulthood

by Ashlee McLardy

In females, peak bone mineral velocity is attained at approximately 12 years of age, with bone mass accrual plateauing at around age 18 years. Optimizing bone accrual during growth is believed to prevent osteoporosis and related fracture risk later in life. A number of lifestyle factors such as physical activity and diet are known to influence bone accrual. In addition, estrogen plays a key role and is a main component affected by oral contraceptives (OC). OC are becoming commonly prescribed for females from 12 years of age. Currently, research on the impact of OC use at this age on bone development is equivocal. Therefore, the purpose of this study was to use a longitudinal study to compare bone mass between OC users and non-users during adolescence and young adulthood. One hundred and twenty-one female participants were drawn from the University of Saskatchewan’s Bone Mineral Accrual Study (BMAS). Participants were grouped based on the initiation and duration of OC use. Bone mineral content (BMC) and areal bone mineral density (aBMD) were assessed by Dual Energy X-Ray absorpitometry. Questionnaires were used to ascertain OC use. BMC and aBMD were assessed between groups at each biological age (BA) using ANCOVA (covariates: height, lean mass, physical activity, vitamin D and calcium). BA is the years from peak height velocity (PHV). Individuals who had initiated OC use after 18 years of age were shown to have, at 30 years of age, significantly less total body (TB) BMC than those individuals that had never used OC. In contrast, persons who initiated OC use between the years of 12 and 18 did not have significantly different TB BMC, between the ages of 20 to 30 when compared to non-users and users who initiated after 18 years of age. OC usage between 12 to 18 years significantly improved lumbar (LS) spine BMC 7 years post PHV. It was found aBMD was not significantly influenced by duration of OC use. When OC use began during adolescence there did not appear to be a detrimental effect on TB bone accrual at 30 years. However, it was found that LS accrual was enhanced at approximately 19 years of age, a difference that was no longer evident by 30 years.