Lactation history and bone mineral density among perimenopausal women

Abstract

To examine the relation between lactation and bone mineral density, we conducted a cross-sectional study among white, nonsmoking, perimenopausal women age 40-54. Three hundred fifty-two women completed a questionnaire covering medical and reproductive histories, physical activity, and diet. We measured the bone density of lumbar vertebrae 2-4 with dual photon absorptiometry, and the midradius and distal radius with single photon absorptiometry. Women with a history of lactation had 41 mg per cm2 higher lumbar bone mineral density than women with no lactation (95% confidence interval = 8-74 mg per cm2), controlling for parity, body mass, physical activity, and menopausal status. We found no important increase at mid- or distal radius.

PIP: Reproductive health specialists used a personal activity computer to measure current physical activity of 352 White women aged 40-54 from central North Carolina. They distributed a questionnaire and simple life calendar to the women to gather information on past physical activity, menopause status, food intake, and health, reproductive, and contraceptive histories. They used dual photon absorptiometry at the second to fourth lumbar vertebrae and single photon absorptiometry at the midradius and the distal radius to measure bone mineral density (BMD). They studied the association between lactation and BMD. 58% of the women had ever breast fed (mean: 14 lifetime months; median: 9 lifetime months). The breast feeding group showed a higher parity, less current physical activity, and less physical activity in high school than their non-breast feeding counterparts. They were similar in education, calcium intake, menopausal status, and history of oral contraceptive use. When the researchers controlled for parity, body mass, current physical activity, and menopausal status, breast feeding women had 41 mg/sq. cm higher lumbar BMD than non-breast feeding women. BMD also increased at the distal radius (10 mg/sq. cm) and midradius (5 mg/sq. cm), albeit more modestly. These findings suggest that lactation has a beneficial effect on calcium homeostasis and BMD.