Influência do exercício físico sobre a massa e o metabolismo ósseo de indivíduos com lesão medular cervical

Abstract

Individuals who stay long time in a wheelchair have significant bone loss, especially in lower limbs that may be aggravated by low calcium intake and inadequate vitamin D status. Physical exercise contributes to maintain or increase bone mass in different populations and may be useful in reducing bone loss in spinal cord injured individuals. The aim of this study was to evaluate the influence of regular physical exercise on bone mass adequacy, biochemical markers of bone metabolism and vitamin D status in individuals with cervical spinal cord injury. Twenty five male adults (19-56 years) with cervical spinal cord injury for at least one year, were recruited and divided into physically active (n=15) and sedentary (n=10) groups. Fasting blood samples were collected and serum samples were stored at -20oC until analysis of calcium, PTH, 25(OH)D, IGF-1, osteocalcin and NTx. Bone mineral content and density (BMD), lean mass and fat mass were evaluated by DXA. Skin pigmentation (constitutive and facultative) was evaluated by reflectance colorimetry in order to investigate its influence on vitamin D status. Habitual calcium intake was recorded using a food frequency questionnaire directed to calcium food sources. Comparisons between groups were performed using Student´s t test except for bone variables that were performed after adjustments for total body mass, duration of injury and calcium intake by analysis of covariance. Associations between variables were evaluated using Pearson's correlation analysis. P values <0.05 were considered significant. There were no significant differences between groups for bone measurements except for lumbar spine Z-score, that was significantly higher in the sedentary group (0.9 ± 1.7 vs -0.7 ± 0.8; p< 0.05). However, in the active group, it was observed that subjects who initiated the practice of physical exercise with less time after injury had higher BMD at the femur (r=-0.60; p<0.05). In active subjects, exercise frequency was negatively associated with serum i-PTH (r = -0.50, p = 0.05) and positively associated with serum 25(OH)D (r= 0.58; p <0.05). After adjustments for total body mass and duration of injury daily calcium intake was positively associated with lumbar spine Z-score (r = 0.73 and p < 0.01) and with radius BMD (r = 0.56 and p <0.05). The results of this study suggest a beneficial effect of regular exercise practice on bone mass and bone-related hormonal profile. The earlier initiation of regular physical exercise after the injury appears to contribute to attenuate the loss of bone mass in lower limbs. Moreover, our results suggest that the osteogenic effect of exercise may be potentiated when combined with an adequate calcium intake.