Table 2 Association between average caffeine intake (g/day) and lumbar bone mineral density (g/cm²).

Exposure	Model 1, β (95% CI)	Model 2, β (95% Cl)	Model 3, β (95% CI)
Average caffeine intake (g/day)	-0.027 (-0.048, -0.007)**	-0.002 (-0.023, 0.019)	0.000 (-0.021, 0.021)
Stratified by age
20–29 years old	-0.015 (-0.057, 0.028)	0.016 (-0.027, 0.058)	0.022 (-0.020, 0.064)
30–39 years old	0.009 (-0.028, 0.046)*	0.040 (0.002, 0.077)	0.040 (0.002, 0.077)*
40–49 years old	-0.054 (-0.086, -0.022)**	-0.035 (-0.068, -0.003)*	-0.033 (-0.065, -0.001)*
Stratified by gender
Male	-0.055 (-0.082, -0.028)***	-0.022 (-0.050, 0.006)	-0.019 (-0.046, 0.009)
Female	0.036 (0.005, 0.068)*	0.039 (0.005, 0.072)*	0.037 (0.004, 0.070)*
Stratified by race
White	-0.004 (-0.035, 0.027)	0.006 (-0.026, 0.038)	0.009 (-0.022, 0.040)
Black	0.026 (-0.063, 0.115)	0.016 (-0.075, 0.107)	0.010 (-0.081, 0.100)
Mexican American	-0.066 (-0.141, 0.009)	-0.027 (-0.104, 0.051)	-0.038 (-0.117, 0.041)
Other race	-0.026 (-0.064, 0.012)	-0.021 (-0.059, 0.017)	-0.024 (-0.062, 0.014)

Model 1: All variables were not adjusted.

Model 2: Age, sex, race were adjusted.

Model 3: All variables were adjusted.

The model is not adjusted for the stratification variable itself in the subgroup analysis.

*P<0.05, **P<0.01, ***P<0.001.