BMI and BMI SDS in childhood: annual increments and conditional change

Figures & data

Table 1. One year increments of body mass index (ΔBMI) according to sex, age and percentile in a sample of 1167 Norwegian children between 2003–2007.

Sex/age	n	ΔBMI/year by percentiles
		10	25	50	75	90
Boys
6	67	−0.3	0.1	0.4	0.6	1.1
7	83	−0.1	0.1	0.5	1.1	2.0
8	70	−0.1	0.2	0.6	1.3	1.8
9	64	−0.5	−0.0	0.5	0.9	2.1
10	76	−0.3	0.2	0.6	1.2	2.0
11	57	−0.6	0.1	0.5	1.0	1.6
12	28	−0.5	0.1	0.7	1.4	2.1
13	71	−0.1	0.4	1.0	1.6	2.5
14	60	−0.1	0.3	0.7	1.1	1.9
Girls
6	68	−0.6	−0.0	0.4	0.7	1.2
7	70	−0.2	0.3	0.6	1.0	1.5
8	94	−0.7	−0.1	0.4	0.7	1.5
9	77	−0.4	0.0	0.4	1.0	1.4
10	80	−0.2	0.0	0.6	1.0	1.6
11	66	−0.3	0.1	0.7	1.1	1.6
12	38	−0.6	0.4	0.8	1.2	1.6
13	53	−0.6	0.2	0.9	1.4	2.0
14	45	−0.7	−0.1	0.5	1.1	1.5

n, number; Age 6: 6.00–6.99, etc.

Table 2. One year increments of BMI SDS (ΔBMI SDS) according to sex, age and percentile in a sample of 1167 Norwegian children between 2003–2007.

Sex/age	n	ΔBMI SDS by percentiles
		10	25	50	75	90
Boys
6	67	−0.30	−0.12	0.07	0.23	0.51
7	83	−0.27	−0.11	0.04	0.27	0.58
8	70	−0.25	−0.10	0.11	0.30	0.53
9	64	−0.54	−0.25	−0.01	0.26	0.45
10	76	−0.33	−0.15	0.04	0.26	0.39
11	57	−0.46	−0.28	−0.04	0.15	0.50
12	28	−0.51	−0.24	0.06	0.31	0.52
13	71	−0.29	−0.10	0.11	0.36	0.58
14	60	−0.30	−0.15	0.01	0.24	0.47
Girls
6	68	−0.52	−0.23	0.01	0.21	0.42
7	70	−0.28	−0.09	0.14	0.30	0.50
8	94	−0.44	−0.21	−0.01	0.16	0.35
9	77	−0.34	−0.16	0.00	0.21	0.41
10	80	−0.37	−0.14	0.04	0.20	0.38
11	66	−0.28	−0.17	0.06	0.26	0.37
12	38	−0.33	−0.09	0.10	0.21	0.48
13	53	−0.69	−0.17	0.16	0.32	0.48
14	45	−0.53	−0.28	−0.07	0.18	0.34

n, number; Age 6: 6.00–6.99, etc.

Table 3. Results from linear regression analysis of 1 year increments of BMI in 1167 Norwegian children (576 boys), 6.00–14.99 years of age/

	Simple regression				Multiple regression			Final model^a
	Unadjusted				Fully adjusted			From backward stepwise selection
Variable	b	95% CI	p	R^2 (R^2adj)	b	95% CI	p	b	95% CI	p
Intercept					−2.812	(−5.540, −0.084)	0.043	−3.246	(−5.805, −0.691)	0.013
Sex			0.026	0.004 0.004)			0.031			0.033
Boys	0.113	(0.013, 0.212)			0.110	(0.010, 0.210)		0.108	(0.019, 0.208)
Girls	0	reference			0	reference		0	reference
Age (years)	0.032	(0.012, 0.052)	0.001	0.009 (0.008)	0.012	(−0.04, 0.064)	0.653	0.002	(−0.046, 0.051)	0.921
Height (cm)	0.005	(0.002, 0.009)	0.001	0.010 (0.009)	0.024	(0.004, 0.044)	0.020	0.026	(0.004, 0.045)	0.008
Weight (kg)	0.006	(0.002, 0.010)	0.004	0.007 (0.006)	−0.036	(−0.070, −0.002)	0.039	−0.041	(−0.074, −0.008)	0.014
BMI (kg/m^2)	0.016	(−0.003, 0.034)	0.093	0.002 (0.002)	0.057	(−0.03, 0.145)	0.200	0.088	(0.017, 0.158)	0.015
WStat			0.613	0.002 (0.001)			0.482
Uw	0.127	(−0.071, 0.324)			0.172	(−0.051, 0.395)
Ow	0.134	(−0.101, 0.368)			0.253	(−0.104, 0.610)
Ob	0.177	(−0.155, 0.509)			0.348	(−0.169, 0.864)
No	0	reference			0	reference
R^2					0.021			0.019
R adj					0.014			0.014

BMI, body mass index; b, estimated regression coefficient; CI, confidence interval; p, p value from F-test; WStat, weight status according to WHO and IOTF classes; Uw, underweight; Ow, overweight; Ob, obese; No, normal weight.

a Interaction between sex and age tested non-significant in the multiple regression and was, therefore, not included.

Table 4. Results from linear regression analysis of 1 year increments of BMI SDS in 1167 Norwegian children (576 boys), 6.00–14.99 years of age.

	Simple regression				Multiple regression^a
	Unadjusted				Fully adjusted
Variable	b	95% CI	p	R^2 (R^2 adj)	b	95% CI	p
Intercept					0.028	(−0.101, 0.157)	0.674
Sex			0.316	0.001 (0.000)			0.230
Boys	0.020	(−0.019, 0.059)			0.024	(−0.015, 0.063)
Girls	0	Reference			0	Reference
Age	−0.006	(−0.013, 0.002)	0.150	0.002 (0.001)	−0.007	(−0.015, 0.001)	0.084
Height SDS	−0.003	(−0.022, 0.017)	0.792	0.000 (0.001)	−0.030	(−0.138, 0.077)	0.580
Weight SDS	−0.030	(−0.049, −0.011)	0.002	0.008 (0.007)	0.077	(−0.130, 0.284)	0.465
BMI SDS*	−0.040	(−0.060, −0.021)	<0.001	0.014 (0.014)	−0.111	(−0.266, 0.045)	0.162
WStat			0.027	0.008 (0.005)			0.484
Uw	−0.020	(−0.098, 0.057)			0.073	(−0.023, 0.169)
Ow	−0.091	(−0.183, 0.000)			0.076	(−0.065, 0.217)
Ob	−0.123	(−0.253, 0.007)			0.068	(−0.118, 0.254)
No	0	Reference			0	Reference
R^2					0.021
R adj					0.014

b: estimated regression coefficient; CI: confidence interval; p: p value from F-test; Wstat: weight status according to WHO and IOTF classes; Uw: underweight; Ow: overweight; Ob: obese; No: normal weight.

a Interaction between sex and age tested non-significant in the multiple regression and was, therefore, omitted.

*By a backward stepwise deletion removing sex, age and thereafter the least significant variable from the multiple regressions we finally ended with only BMI SDS by first measurement as significant.

Figure 1. Correlation between standard deviation scores of the BMI (BMI SDS) and BMI SDS after 1 year in annual age groups from 6.00–14.99 years of age.

Figure 2. Distribution of standard deviation scores of 1 year conditional change in BMI in 1167 Norwegian children from 6.00–14.99 years of age.