Weighted characteristics of the study sample：the cohort of adults aged 30–69 (n=7500)
| Lumbar BMD Q1 (g/cm²) (n=1873) | Lumbar BMD Q2 (g/cm²) (n=1869) | Lumbar BMD Q3 (g/cm²) (n=1882) | Lumbar BMD Q4 (g/cm²) (n=1876) | P value | |
| Age (years） | 46.4±8.7 | 44.5±8.6 | 44.0±8.7 | 44.2±8.6 | <0.05 |
| Gender | <0.05 | ||||
| Men/women | 55.6/44.4 | 49.8/50.2 | 48.9/51.1 | 50.7/49.3 | |
| Race | <0.05 | ||||
| Mexican American | 11.2 | 11.5 | 9.0 | 4.9 | |
| Other Hispanic | 8.0 | 6.7 | 5.6 | 4.9 | |
| Non-Hispanic white | 64.6 | 62.6 | 66.5 | 64.5 | |
| Non-Hispanic black | 5.9 | 8.4 | 10.8 | 17.7 | |
| Other race, including multiracial | 10.3 | 10.8 | 8.1 | 8.0 | |
| Blood urea nitrogen(mmol/L） | 4.7±1.6 | 4.7±1.5 | 4.6±1.5 | 4.7±1.7 | 0.19 |
| Serum calcium (mmol/L） | 2.3±0.1 | 2.3±0.1 | 2.3±0.1 | 2.3±0.1 | 0.92 |
| Serum creatinine (μmol/L） | 74.9±19.6 | 75.8±23.6 | 75.9±28.8 | 78.7±32.0 | <0.05 |
| Serum glucose (mmol/L） | 5.5±1.6 | 5.5±2.0 | 5.5±1.9 | 5.6±2.3 | 0.15 |
| Serum phosphorus (mmol/L） | 1.2±0.2 | 1.2±0.2 | 1.2±0.2 | 1.2±0.2 | <0.05 |
| Serum sodium (mmol/L） | 139.2±2.3 | 139.3±2.3 | 139.1±2.3 | 139.1±2.2 | 0.19 |
| Serum 25-hydroxyvitamin D (nmol/L) | 67.3±26.6 | 67.5±25.8 | 70.1±27.6 | 68.2±26.4 | <0.05 |
| Alkaline phosphatase (U/L） | 73.3±27.0 | 69.1±22.3 | 65.4±20.1 | 64.2±23.1 | <0.05 |
| Total cholesterol (mmol/L） | 5.3±1.1 | 5.2±1.1 | 5.1±1.0 | 5.0±1.0 | <0.05 |
| Total protein (g/L） | 71.0±4.5 | 70.9±4.3 | 71.1±4.5 | 71.1±4.1 | 0.61 |
| Serum uric acid (μmol/L） | 319.8±78.3 | 321.5±83.5 | 314.4±82.6 | 321.2±83.6 | <0.05 |
| Serum potassium (mmol/L） | 4.0±0.3 | 4.0±0.3 | 3.9±0.3 | 4.0±0.3 | <0.05 |
| BMI (kg/m2） | 29.3±6.1 | 29.7±6.6 | 29.2±6.7 | 30.3±7.3 | <0.05 |
| Serum triglycerides (mmol/L） | 1.9±1.4 | 1.9±1.9 | 1.8±1.3 | 1.7±1.4 | <0.05 |
| Education level | <0.05 | ||||
| Less than 9th grade | 6.9 | 4.3 | 3.1 | 2.0 | |
| 9–11th grade (includes 12th grade with no diploma) | 11.2 | 9.3 | 7.8 | 7.9 | |
| High school graduate/General Educational Development or equivalent | 21.5 | 22.1 | 19.0 | 19.5 | |
| Some college or associates degree | 30.5 | 30.6 | 32.0 | 32.0 | |
| College graduate or above | 29.9 | 33.7 | 38.1 | 38.6 | |
| Vigorous recreational activities | <0.05 | ||||
| Yes | 22.7 | 28.8 | 31.6 | 33.3 | |
| No | 77.3 | 71.2 | 68.4 | 66.7 | |
| Smoked at least 100 cigarettes in life | <0.05 | ||||
| Yes | 47.6 | 42.6 | 42.1 | 42.8 | |
| No | 52.4 | 57.4 | 57.9 | 57.2 | |
| Stones | <0.05 | ||||
| Yes | 13.7 | 9.2 | 9.4 | 8.6 | |
| No | 86.3 | 90.8 | 90.6 | 91.4 | |
| Ratio of family income to poverty | <0.05 | ||||
| <1.99 | 35.8 | 33.7 | 28.9 | 28.9 | |
| 1.99–3.49 | 21.0 | 22.8 | 21.0 | 21.6 | |
| >3.49 | 43.2 | 43.5 | 50.1 | 49.5 |
Notes: Mean±SD for continuous variables: p value was calculated by weighted linear regression model; % for categorical variables: p value was calculated by weighted χ2 test.
BMI, body mass index; BUN, blood urea nitrogen.