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Title: Oral progestogen-only contraception may protect against loss of bone mass in breast-feeding women.
Author: Caird LE, Reid-Thomas V, Hannan WJ, Gow S, Glasier AF.
Journal: Clin Endocrinol (Oxf); 1994 Dec; 41(6):739-45. PubMed ID: 7889609.
Abstract:
BACKGROUND AND OBJECTIVES: A worldwide trend towards increasing life expectancy has meant that osteoporosis is emerging as an important public health problem. The loss of bone mineral density and its restoration in association with a premenopausal but physiological hypo-oestrogenic state may serve as an important model for research into the pathogenesis and prevention of osteoporosis. With this in mind we have undertaken a longitudinal study of changes in bone mineral density over one year in women after childbirth. DESIGN: Observational study of 31 women in the first year following childbirth; 11 intending to breast-feed and use barrier methods of contraception, 9 intending to breastfeed and to use the progestogen-only pill and 10 intending to artificially feed and to use barrier methods. PATIENTS: Recruitment was from the antenatal clinics of the Simpson Memorial Maternity Pavilion. Only non-smokers who had regular menstrual cycles prior to conception were included. MEASUREMENTS: Bone mineral density was measured at the lumbar spine within 3 weeks of childbirth and repeated at 6 and 12 months post partum. Plasma oestradiol, prolactin and osteocalcin concentrations were measured at each visit. RESULTS: Breast-feeding women using barrier methods lost a mean +/- SE of 4.9 +/- 1.5% of bone mineral density in the first 6 months following delivery. This was however reversible since by one year the bone mineral density was no different from that measured immediately post partum. Breast-feeding women using the progestogen-only pill lost a significantly smaller percentage of bone mineral density in 6 months and by one year bone mineral density was 2.95 +/- 0.75% higher than post partum. Artificially feeding women had a steady increase in bone mineral density in the first year and bone mineral density was on average 4.3 +/- 1.2% higher. CONCLUSION: Breast-feeding results in a reversible reduction in spinal bone mineral density. The small amounts of gestagen in the progesterone-only pill would appear to protect against this loss. The mechanism of this loss in bone mineral density and the potentially bone protective effects of gestagens require further study. The findings of a longitudinal study of lactation-related changes in bone mineral density in the first postpartum year suggest that use of progestogen-only oral contraceptives (OCs) may reduce this loss. 28 nonsmoking women were recruited from the postnatal wards at Edinburgh's Simpson Memorial Maternity Pavilion and divided into three groups according to intended postpartum contraceptive methods: group A (9 women who planned to breast feed and use barrier methods); group B (9 women who planned to breast feed and take a progestogen-only OC); and group C (10 women who were going to bottle feed and use a barrier method). Bone mineral density was measured at the lumbar spine within 3 weeks postpartum and again at 6 and 12 months postpartum. In group A, there was a significant (p 0.001) decrease in bone mineral density between 3 weeks and 6 months postpartum and a return to the puerperium level by 12 months. In group B, 7 of the 9 women lost bone mineral density from delivery to 6 months, although the loss was less significant (p 0.01) than that recorded in group A, but by 12 months, bone mineral density exceeded that at delivery. In group C, only 2 of 10 women experienced any bone mineral density loss and densities at 12 months again approximated those at delivery. The apparent protective effect of progestogen against bone mass loss could have important implications for the prevention of osteoporosis in menopausal and post-menopausal women.

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