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Background & objectives: Obesity and osteoporosis are major problem that their prevalence is increasing. Physical activity can be effective in the prevention of osteoporosis by some mechanisms such as changes in anthropometrics variables. Body mass index (BMI) in men and women is closely related to bone mineral density (BMD). However, the relationship varies between BMI and BMD according to the  different studies. Therefore, the aim of this study was to investigate the relationship between body mass index and lumbar bone mineral density in active and inactive middle-aged women.
Methods: Sixty active, middle-aged women and 60 inactive women in the age range of 50 to 65 years, with medical records and clinical trials were selected in Milad Hospital in Tehran. Body mass index was calculated and bone mineral density was measured by DEXA scan in the lumbar spine (L₁ to L₄). Independent t-test and Pearson correlation coefficient were used to evaluate the data. SPSS software version 26 was used for data analysis.
Results: The results of this study showed that in the active group in L₁, L₃ and L₄ lumbar vertebrae (p=0.034, p=0.017, p=0.019, respectively), and in the inactive group in L₃ and L₄ vertebrae (p=0.034, p=0.022, respectively), there was a positive and significant relationship between body mass index and bone mineral density. No significant relationship was found in other lumbar vertebrae of both groups.
Conclusion: The results of the present study showed that weight gain and consequently BMI among active women reduce the risk of osteoporosis. Physical activity in women seems to lead to more muscle mass, which in turn leads to an increase in bone mineral density. Considering this issue, it can be said that one of the applications of the results of the present study is the use of this index in predicting the bone density of individuals