Bone mineral density in a native population of Argentina with low calcium intake

To determine the bone mineral density (BMD) of a group of natives from Tafi del Valle, Argentina, to examine possible differences compared to other populations.

BMD of lumbar spine and proximal femur was evaluated by dual x-ray absorptiometry (DEXA), in volunteer natives of El Potrerillo y El Rincon (descendants of the Amaichas and Quilmes). Forty-seven women and 31 men between 20 and 80 years of age were assessed. Average daily intake of calcium, physical activity level, serum levels of 25-OH vitamin D (25-OH-D), calcium, phosphorus and alkaline phosphatase were also determined.

Average calcium intake was 345 +/- 22.4 mg/day (mean +/- SD). The average sunlight exposure was 3.8 +/- 0.44 h. Degree of physical activity was moderate/hard (grade 4) to very hard (grade 6) in those 60 yrs of age or younger. Laboratory values were normal except for 25-OH-D levels, which were significantly greater in Tafi del Valle (26.8 ng/ml) than in Buenos Aires (20.7 ng/ml); (p < 0.05) BMD of the proximal femur of both sexes was significantly greater compared to the reference groups; Z score of the female population was femoral neck: +/- 0.64 (p < 0.05); Ward's triangle: +/- 0.64 (p < 0.001); trochanter: +/- 0.90 (p < 0.001). Among men, femoral neck: +/- 0.53 (p < 0.01); Ward's triangle: +/- 1.45 (p < 0.001); trochanter: +/- 0.95 (p < 0.001). No significant differences were observed in the lumbar spine BMD. The high physical activity required by the mountainous land of Tafi del Valle may be the cause of increased BMD at the proximal femur among these people. High values of vitamin D produced by increased sun exposure can lead to greater absorption of calcium despite low calcium intake.

Greater physical activity, higher levels of vitamin D, and racial factors in the native population could explain the greater BMD seen in the proximal femur despite low calcium intake.