Relationship between reproductive factors and bone mineral density in postmenopausal women

Background
Many studies have assessed the protective factors and risk factors of osteoporosis in postmenopausal women. Considering the uncertainty about the effects of reproductive factors on bone density and the scarcity of information about postmenopausal women in Iran, the present study was conducted.

Objectives
This study aimed to investigate the relationship between reproductive factors and bone density in postmenopausal women.

Material and methods
In this cross-sectional study, 600 postmenopausal women without any known condition affecting bone mineral density were selected through convenience sampling from among the women referred to the densitometry center of Golestan Hospital in Ahwaz, Iran. The data were collected through questionnaires on demographics and reproduction. Bone mineral density was measured by the DEXA method using a Hologic machine in the L1–L4 region and the femoral neck. The demographic and reproductive variables were compared in 3 groups (osteoporosis, osteopenia and normal BMD).

Results
The frequencies of osteoporosis and osteopenia were 15.16% and 57.33%, respectively. All reproductive factors were significantly different in the 3 groups. Multinomial logistic regression revealed later menarche to be a significant risk factor for osteopenia (OR = 4.36, CI = 3.38–5.63, p = 0.001) and osteoporosis (OR = 2.63, CI = 2.00–3.46, p = 0.001). A higher number of parity and longer breastfeeding were also revealed to be other risk factors; older age at first pregnancy is a protective factor. A higher BMI was found to be a protective factor only for osteoporosis.

Conclusions
Our results suggest that later menarche, multiparity and longer breastfeeding act as risk factors, while higher BMI and older age at first pregnancy act as protective factors for bone density disorders in postmenopausal women.