Oral progestogen-only contraception may protect against loss of bone mass in breast-feeding women.
OBJECTIVE
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.


METHODS
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.


METHODS
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.


METHODS
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.


CONCLUSIONS
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.
Caird
L E
LE
Department of Obstetrics and Gynaecology, University of Edinburgh, UK.
Reid-Thomas
V
V
Hannan
W J
WJ
Gow
S
S
Glasier
A F
AF
D000328:Adult; D000469:Alkaline Phosphatase / Q000097:blood; D015519:Bone Density / Q000187:drug effects*; D001903:Bottle Feeding; D004958:Estradiol / Q000097:blood; D005260:Female; D006801:Humans; D007774:Lactation / Q000378:metabolism*; D016912:Levonorgestrel / Q000008:administration & dosage; D008137:Longitudinal Studies; D009640:Norethindrone / Q000008:administration & dosage; D015675:Osteocalcin / Q000097:blood; D045167:Progesterone Congeners / Q000008:administration & dosage*; D011388:Prolactin / Q000097:blood
D045167:Progesterone Congeners; D015675:Osteocalcin; D004958:Estradiol; D016912:Levonorgestrel; D011388:Prolactin; D000469:Alkaline Phosphatase; D009640:Norethindrone