[On correlation between body mass index and lumbar spine average bone mineral density: a study in male patients with osteopenia and those with osteoporosis].

From among the patients who visited the Dept. of Rehabilitation of West China Hospital for arthalgia in the period from Aug. 2003 to Dec. 2005, we recruited 566 male patients who were over 40 years of age and did not have hyperostosis in the lumbar spine, and whose T scores were each less than--1. Their ages ranged from 40 to 93 years, and the average age was 62.93 +/- 13.50. The dual-energy X-ray absorptiometry from DMS Company in France was used to measure the bone density of the L2-4 anterior-posterior. The basic data about the subjects, containing the age, height, weight, diabetes mellitus, exercise and smoking or not, were recorded. Then the body mass index were calculated. In accordance to the T score, the subjects were separated into two groups: osteopenia group and osteoporosis group. In comparison of the basic data between groups, BMI of osteoporosis group was significantly higher than that of the osteopenia group, but the number of the subjects who exercised was smaller (P < 0.05). Multiple linear regression analysis revealed that in the case BMI increased by 1 kg/m2, BMD significantly decreased by 0.003 g/cm2 (P = 0.002), and the age negatively correlated with BMD (B = -0.001, P = 0.035). "Exercise or not" was positively related to BMD (B = 0.028, P = 0.000). "Smoking or not" and BMD were not significantly correlated (P = 0.837). In conclusion, increase of BMI, or we may say, increase of fat, would decrease the lumbar spine average BMD in the patients of osteoporosis or osteopenia. Some reports have pointed out that only by increasing BMI with increased amount of muscles, but not with increased amount of fat, would be beneficial to the prevention of osteoporosis. So we concluded that the muscle amount in the subjects should be taken into account when we probe into the relation between BMI and BMD.