Body mass index at 11 years and bone mass at age 18: path analysis within the 1993 Pelotas (Brazil) birth cohort study

Table 2 Association between body mass index (BMI) z score at 11 years old and bone mass at 18 years mediated by BMI z score, fat mass and fat free mass at 18 years among men

Association entre BMI z score at 11 y and BMC/BMD	BMC (g)		BMD (g/cm²)
	β (95% CI)p-value		β (95% CI)p-value
	Association	% mediation	Association	% mediation
Overall association^(A)	179.714(161.401; 198.027)p < 0.001	n/a	0.030(0.024; 0.035)p < 0.001	n/a
Association after accounting for mediation by BMI z score at 18 years old^(B)	25.764(8.536; 42.993)p = 0.003	85.7	0.005(−0.0004; 0.010)p = 0.068	83.3
Association after accounting for mediation by fat mass at 18 years old^(B)	167.344(151.041; 183.648)p < 0.001	6.9	0.037(0.032; 0.041)p < 0.001	-^a
Association after accounting for mediation by fat free mass at 18 years old^(B)	38.820(27.874; 49.766)p < 0.001	78.4	−0.003(−0.007; −0.0001)p = 0.044	90.0
Association after accounting for mediation by BMI z score, fat mass and fat free mass at 18 years old^(B)	20. 375(6.717; 34.033)p = 0.003	88.7	0.003(−0.001; 0.007)p = 0.160	90.0

The 1993 Pelotas Birth Cohort. Brazil. N = 1601 males.
β - Linear regression coefficient; 95% CI - 95% confidence interval; p-value from Wald’s test; BMC - bone mineral content; BMD - bone mineral density; BMI - body mass index; BMI z score: according to the World Health Organization for children and teenagers from 5 to 19 years.
% mediation = 100 - (Direct effect/Total effect)*100, ie, 100 - (B/A)*100
^aPercentage of mediation cannot be calculated because of the negative association of FM with BMD in males.

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