Both indirect maternal and direct fetal genetic effects reflect the observational relationship between higher birth weight and lower adult bone mass

Table 1 The analyses between birth weight and BMC, bone area, BMCadjArea, and BMD in UK Biobank dataset

Measurement	Site	Outcome	Effect	Se	P
DXA	Lumbar spine (LS, N = 20,367)	BMC	0.06	0.01	2.87 × 10⁻⁷
		Bone area	0.17	0.01	< 2.00 × 10⁻¹⁶
		BMD	− 0.04	0.01	0.007
		BMCadjArea	− 0.01	0.01	2.27 × 10⁻¹⁴
	Lateral spine (LaS, N = 21,364)	BMC	− 0.002	0.01	0.83
		Bone area	0.02	0.01	0.04
		BMD	− 0.03	0.01	0.02
		BMCadjArea	− 0.05	0.01	0.001
QUS	Heel (N=177,675)	BMD	− 0.06	0.01	< 2.00 × 10⁻¹⁶

BMCadjArea: the linear regression for BMC with independent variable bone area, and the residual of BMC for each individual was predicted, then, the BMCadjArea of each individual was calculated as the sum of the mean of BMC and the residual
Exposure: measured birth weight
Outcome: BMC, bone area, BMCadjArea, and BMD. The measurements of the outcomes were standardized (z-scores) to give a mean = 0 and standard deviation = 1 to ease comparison
All analyses were adjusted for sex, age, weight, smoking, alcohol, and physical activity

ISSN: 1741-7015