Association between depot medroxyprogesterone acetate (DMPA), physical activity and bone health.

Physical activity has been advocated for women in the hope of offsetting progestin-only contraceptive-related loss in bone mineral density. There is limited evidence for the beneficial effect of physical activity on bone health of hypo-oestrogenic premenopausal women. The aim of this cross-sectional study was to examine the relationship between physical activity and bone health [as measured by quantitative ultrasound (QUS)] of depot-medroxyprogesterone acetate (DMPA) users, and to investigate whether QUS measurements of DMPA users and non-users differed according to physical activity. Bone health of 48 DMPA users and 48 age-matched controls (22.83 ± 3.2 years) was assessed using calcaneal broadband ultrasound attenuation (BUA). Participants were categorised into low and high levels of physical activity based on their exposure to bone-loading exercise. Analysis of covariance was conducted to determine if QUS measurements of DMPA users and non-DMPA users differed within levels of bone-loading physical activity after controlling for body mass index. The duration of DMPA use ranged from 6 to 132 months. Participants' reference bone-loading exposure time averaged 3.3 ± 1.8 years. Data analysis revealed that DMPA users had significantly lower BUA by 6.54 dB/MHz (t (95) = -2.411, p = 0.018) compared to non-users of DMPA. Concurrently high levels of physical activity and DMPA use led to 1.996 dB/MHz decreases in BUA. A cycle of prolonged DMPA use and concurrent engagement in high levels of physical activity appears detrimental to bone health. It is suggested that the lack of oestrogen may counteract the effects of physical activity by inhibiting bone formation in response to mechanical bone-loading.