Associations between serum calcium, 25(OH)D level and bone mineral density in older adults

Calcium and vitamin D play important roles in bone health as essential nutrients. We explored whether serum calcium, 25(OH)D were associated with bone mineral density (BMD) in older adults. This cross-sectional study was conducted on a sample of 4595 participants (2281 men and 2314 women) aged ≥ 50 years (from 50 to 85 years, 60.1 ± 8.7 years for men and 62.0 ± 9.7 years for women) from the National Health and Nutrition Examination Survey (NHANES) 2001–2006. The independent variables were serum calcium and 25(OH)D. The dependent variable was lumbar BMD. The other variables were considered potential effect modifiers. We performed weighted multivariate linear regression models and smooth curve fittings to evaluate the associations between them. Subgroup analyses were also performed. We observed a negative association between serum calcium and lumbar BMD in the fully adjusted model. In the subgroup analyses, this association was no longer significant among males and other race/ethnicity. On the other hand, there was a positive association between serum 25(OH)D and lumbar BMD in the fully adjusted model. In the subgroup analyses, this association did not differ in different age groups, between men and women. However, the association between serum 25(OH)D and lumbar BMD followed a U-shaped curve in Mexican Americans. This cross-sectional study indicated that serum calcium negatively correlated with lumbar BMD, and serum 25(OH)D positively correlated with lumbar BMD in older adults. However, the association between serum calcium and lumbar BMD in males followed a U-shaped curve.