Background Body weight is highly related to bone mineral density (BMD), regardless of age, menopausal duration, or any other variables. Low body mass index (BMI) constitutes a risk for fragility fractures. Thin postmenopausal women are more at risk of developing non-traumatic fractures.
Fatness is positively associated with BMD, both at weight-bearing and non-weight-bearing sites. Therefore, it is presumable that the both mechanical load, induced by greater body weight, and hormonal factors, through the effects of adipose tissue on levels of circulating estrogens, are responsible for greater skeletal density in obese people.
Objectives The aim of the present study was to demonstrate the correlation between BMI and BMD evaluated at the distal radius. That site has been chosen because it is a non-weight-bearing area and consequently it is not influenced by the mechanical load.
Methods A total of 712 Caucasian menopausal women, aged 41–100 years (mean age 65, mean duration of menopause 17,4 yrs.) was studied. The sample was divided into 4 groups according to BMI (modified WHO classification): underweight (BMI18.5–24.9, 315 patients, mean age 64,5 yrs., mean duration of menopause 17,2 yrs.), overweight (BMI >25–29.9, 270 patients, mean age 66.1 yrs., mean duration of menopause 18,6 yrs.), obese (BMI >30; 133 patients, mean age 63.8 yrs., mean duration of menopause 15.3 yrs).
BMD was studied using dual-energy X-ray absorptiometry (HOLOGIC DTX 100). The examinations were performed on the distal radius of the non-dominant forearm. Diagnosis of osteoporosis was made according to the WHO report (T score <-2.5 SD: osteoporosis. T score ?1 to -2.5 SD: osteopenia. T score 0 to ?1 SD: normal). The ANOVA procedure and the Chi square test were used for statistical analysis of the results.
Results Results are reported on Table 1.
Conclusion As expected, the mean value of BMD was higher in the obese group (p < 0.000001). The analysis of prevalence of osteoporosis and osteopenia in all the groups studied showed a negative correlation between body size and bone mass loss. In particular it was observed the finding of a progressive reduction of the number of osteoporotic women with the increasing BMI, while the percentage of osteopenic subjects was almost constant (p < 0.004).
The importance of the present study was the demonstration of a strong positive correlation between BMI and BMD at non-weight-bearing site. The findings confirms the protective role of adipose tissue on the bone independently of the influence of the mechanical load.
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