Dear editor: Osteoporosis is a condition prevalent among elderly, predominantly in women, with morbid consequences pointing to the importance of its prevention.

Several factors well-known contribute to loss of bone mineral density (BMD). Interestingly, urine calcium excretion predicts bone loss in idiopathic hypercalciuria. BMD loss and hypercalciuria are associated with dietary calcium intake and body weight, indicating that some innate characteristics of the skeletal tissue, kidney, and intestine may affect the clinical course of bone loss in hypercalciuric patients, operating as a metabolic disorder.¹1. Sella S, Cattelan C, Realdi G, Giannini S. Bone disease in primary hypercalciuria. Clin Cases Miner Bone Metab. 2008;5(2):118-26. The excessive sodium intake might also accelerate bone reabsorption.²2. Park SM, Joung JY, Cho YY, Sohn SY, Hur KY, Kim JH, et al. Effect of high dietary sodium on bone turnover markers and urinary calcium excretion in Korean postmenopausal women with low bone mass. Eur J Clin Nutr. 2015;69(3):361-6. https://doi.org/10.1038/ejcn.2014.284
https://doi.org/10.1038/ejcn.2014.284...

This study is part of the Digitalis Study, a cross-sectional investigation with a random sample of a registered population in the Niteroi Family Doctor Program, State of Rio de Janeiro, Brazil. The objective was to test the association of osteopenia or osteoporosis with hypercalciuria and excessive sodium intake.

All the participants (220 women and 146 men, 45 to 99 years old) undergo the DXA exam biochemical serum and urine analysis.

The prevalence rate was 44.1% for osteopenia and 8% of osteoporosis. These numbers are lower than the ones reported for Latin American countries, where prevalence rates for osteopenia ranged from 46 to 57.2% and for osteoporosis from 7.9 to 22%.³3. Morales-Torres J, Gutiérrez-Ureña S. Osteoporosis Committee of Pan-American League of Associations for Rheumatology. The burden of osteoporosis in Latin America. Osteoporos Int. 2004;15(8):625-32. https://doi.org/10.1007/s00198-004-1596-3
https://doi.org/10.1007/s00198-004-1596-... Besides the genetic profile and environmental factors, this divergence could be accounted for by low protein and calcium intake during bone formation, conditions that have already been associated with a higher risk of osteoporosis development.⁴4. Rizzoli R. Dairy products, yogurts, and bone health. Am J Clin Nutr. 2014;99(Suppl 5):1256S-62S. https://doi.org/10.3945/ajcn.113.073056
https://doi.org/10.3945/ajcn.113.073056...

Patients with hypercalciuria often excrete more calcium than they absorb, reflecting a net loss of total body calcium.⁵5. Bushinsky DA, Asplin JR, Grynpas MD, Evan AP, Parker WR, Alexander KM, et al. Calcium oxalate stone formation in genetic hypercalciuric stone-forming rats. Kidney Int. 2002;61(3):975-87. https://doi.org/10.1046/j.1523-1755.2002.00190.x
https://doi.org/10.1046/j.1523-1755.2002... In the present study, an excessive urinary calcium excretion was associated with osteoporosis in women, but not to osteopenia. In the multiple logistical regression analysis, the effect of an excessive urinary calcium excretion on osteoporosis, independent of the gender or BMI, was substantial (OR= 3.26 and p<0.05).

Previous studies have also suggested that the intake of nutrients such as sodium is related to calcium excretion and to BMD.²2. Park SM, Joung JY, Cho YY, Sohn SY, Hur KY, Kim JH, et al. Effect of high dietary sodium on bone turnover markers and urinary calcium excretion in Korean postmenopausal women with low bone mass. Eur J Clin Nutr. 2015;69(3):361-6. https://doi.org/10.1038/ejcn.2014.284
https://doi.org/10.1038/ejcn.2014.284... The association of sodium intake with osteoporosis was not statistically significant in our study.

Our results also confirm the importance of traditional risk factors (gender, age, BMI and skin color) and highlight the role of a high calcium urinary excretion as an independent factor associated with osteoporosis.

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