Impact of Body Mass Index (BMI) and Parity upon Bone Mineral Density (BMD) Using DEXA in Pakistani Women

Abstract

Objective: The purpose of this study was to find out correlation between body mass index (BMI) and bone mineral density (BMD) using dual energy X-ray absorptiometry (DEXA) as gold standard in Pakistani women.

Material and Methods: This prospective study was performed at Department of Nuclear Medicine, Dr Ziauddin Medical University Hospital, Karachi, Pakistan from April 2013 to June 2013. We included 173 consecutive females who had DEXA done over hips and lumbar spine using Lunar Prodigy Advance, USA.  Based on WHO criteria for obesity, women were classified as obese with BMI ≥30 Kg/m² and non-obese <30 Kg/m^2.

Results: 119 women were non-obese (mean age of 61 ±13 years; 107 post-menopausal) while 54 women were obese (mean age of 59 ±11 years; 48 post-menopausal). Mean parity in both groups was 04 ±02 (non-significant p value). Hypertension was more prevalent in obese women (p<0.05). BMD over total hips and femoral necks was significantly higher in obese while spinal BMD was not significantly different among two groups. Low BMD was found in 90 (76%) non-obese and 33 (61%) obese (non-significant P-values). Menopause and parity were found to be significant confounding factors in non-obese for low BMD (P<0.05). In non-obese, number of parity was found to have a significant linear but negative impact on BMD. In obese, parity was found to have a rather protective effect up to parity 6 after which a significant fall in BMD was noted. Receiver operating characteristic (ROC) curve analysis was used which revealed a cut-off BMI value of 27.055 Kg/m² for obesity in studied population.

Conclusion: We conclude that obese women had significantly higher BMD values over hip and femoral neck than non-obese women. Menopause and parity were found to enhance relative risk for low BMD in non-obese women. Parity upto 6 was found to have protective role in obese women but after 6 they are at same risk as non-obese women. Prevalence of low BMD was higher but non-significant in non-obese according to WHO’s cut-off value for European population. But using a cut-off BMI of ≤27.055 Kg/m² in our population, significantly higher incidence of low BMD noted in non-obese studied population.

Key words: Osteoporosis; DEXA; BMD; Obesity; BMI; Parity; Menopause