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

Table 3 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 females

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)	179.945(165.306; 194.584)p < 0.001	n/a	0.029(0.025; 0.033)p < 0.001	n/a
Association after accounting for mediation by BMI z score at 18 years old^(B)	56.571(42.714; 70.428)p < 0.001	68.6	0.011(0.007; 0.015)p < 0.001	62.1
Association after accounting for mediation by fat mass at 18 years old^(B)	122.570(109.272; 135.869)p < 0.001	31.9	0.025(0.022; 0.029)p < 0.001	13.8
Association after accounting for mediation by fat free mass at 18 years old^(B)	73.100(61.975; 84.225)p < 0.001	59.4	0.003(0.0004; 0.006)p = 0.024	89.7
Association after accounting for mediation by BMI z score, fat mass and fat free mass at 18 years old^(B)	43.008(30.140; 55.875)p < 0.001	76.1	0.007(0.003; 0.010)p < 0.001	75.9

The 1993 Pelotas Birth Cohort. Brazil. N = 1706 females.
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

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