Table 1.

Demographic characteristics of participants aged 4–12 years with a complete 24-h urine collection at baseline and follow-up

Characteristic	Baseline (n 666)		Follow-up (n 161)		P-value*
	n or mean	% or se	n or mean	% or se
Age (years)	9·3	0·1	9·9	0·4	<0·001
Age group
4–8 years	283	43	48	30	0·003
9–12 years	383	57	113	70
Sex
Boy	365	55	84	52	0·55
Girl	301	45	77	48
Parental educational attainment†
Low	137	24	18	13	0·01
Mid	85	15	26	18
High	348	61	99	69
Socio-economic disadvantage‡
Bottom tertile (most disadvantaged)	108	16	51	32	<0·001
Mid tertile	148	22	62	39
Top tertile (least disadvantaged)	410	62	48	30
School type
Non-government	227	34	51	32	0·56
Government	439	66	110	68
Weight category§
Underweight	67	10	8	5	0·09
Healthy weight	487	73	132	82
Overweight	92	14	16	10
Obese	20	3	5	3
BMI Z-score‖	0·10	1·05	0·17	0·91	0·43
Day of urine collection
School day	317	48	62	39	0·04
Non-school day	349	52	99	62

^* P-value determined via Pearson’s χ² test or independent t test.

^†Missing data at baseline n 96, follow-up n 19.

^‡Based on school postcode and corresponding Socio-Economic Indexes for Areas, Index of Relative Socioeconomic Disadvantage.

^§Weight classification based on the International Obesity Task Force BMI reference cut-offs⁽²⁸⁾.

^‖BMI Z-scores calculated using the 2000 US Centres for Disease Control and Prevention (CDC) Growth Charts as the reference population⁽²⁷⁾.