Body mass index and gynecological factors as determinants of bone mass in healthy Moroccan women

Several studies have shown that low body mass index (BMI) is associated with low BMD and fractures. However, the results that have been published from studies on reproductive factors and BMD are extremely controversial, with some demonstrating a beneficial effect, while others show a detrimental impact of these factors on bone mass.

Objective

To study the influence of several gynecological factors (years since menopause (YSM), age at menarche and gynecological age or reproductive life) simultaneously with anthropometric factors as determinants of bone mineral density (BMD) in healthy women older than 40.

Methods

BMD was determined by dual energy X-ray absorptiometry (DXA) at the lumbar spine and femurs in women aged >40 randomly chosen from the population of Rabat with a cluster sampling method.

Results

Four hundred and twenty-two healthy women older than 40 years were included in the study. The mean age was 57.2 years (8.4) 40–79] and the mean number of parities was 4.42 (2.9) 0–14]. Osteoporosis according to the classification of WHO (T-score ≤ ?2.5) was observed in 133 women (32.2%). The increase in the number of parities was associated to a larger body mass index and a lower BMD as well in the hips and the lumbar spine after adjustment for age. The comparison of groups of patients according to the age at menarche, the age at menopause or the period of fertility did not highlight an association with BMD. BMD at the lumbar spine and the hips was correlated negatively with age, YSM and parity and positively with BMI. Multivariate analysis showed that the determinant of BMD are BMI (OR = 0.88; 95% CI: 0.83–0.92), parity (OR = 1.10; 1.01–1.56) and YSM (OR = 1.06; 1.03–1.10).

Conclusion

Bone loss in women older than 40 is a function of aging, parity and years since menopause; and there is a definite bone-protective effect of body mass weight. Further studies are required to evaluate the role of these parameters in the fracture risk.