# Table 5 BMI, BMI standard deviation score (SDS)a and changes during childhood/adolescence according to weight classb

Age/ age interval Thin/normal weight at 2–4 years of age  (n = 471) Overweight/obese at 2–4 years of age  (n = 61)   Thin/normal weight at 5–7 years of age  (n = 459) Overweight/obese at 5–7 years of age  (n = 73)
Mean (SD) Mean (SD) p-value Mean (SD) Mean (SD) p-value
BMI kg/m2
2–4 years 15.94 (1.06) 18.71 (0.89) <0.001
5–7 years 15.54 (1.50) 18.32 (2.92) <0.001 15.27 (1.01) 19.53 (2.29) <0.001
15–17 years 21.80 (3.82) 25.09 (5.74) <0.001 21.31 (3.08) 27.63 (5.95) <0.001
Change in BMI kg/m2
to 5–7 years −0.40 (1.29) −0.39 (2.74) 0.051
to 15–17 years 5.85 (3.66) 6.38 (5.73) 0.66 6.03 (2.76) 8.10 (4.84) 0.001
BMI SDS
2–4 years −0.17 (0.84) 1.73 (0.47) <0.001
5–7 years 0.07 (0.88) 1.45 (1.10) <0.001 −0.06 (0.70) 2.03 (0.72) <0.001
15–17 years 0.35 (1.04) 1.13 (1.12) <0.001 0.25 (0.95) 1.69 (1.01) <0.001
Change in BMI SDS
to 5–7 years 0.24 (0.78) −0.29 (1.02) <0.001
to 15–17 years 0.53 (1.11) −0.60 (1.14) <0.001 0.30 (0.85) −0.34 (0.84) <0.001
1. A sub study of The Tromsø Study: Fit Futures N = 532: 279 boys, 253 girls
2. aBMI SDS is calculated using LMS values based on an international reference population of children [28]
3. bWeight classes are based on BMI according to the International Obesity Taskforce’s age- and sex-specific cut-off values in children 2–18 years: thinness: adult BMI <18.5 kg/m2, normal weight: adult BMI ≥18.5- < 25 kg/m2, overweight: adult BMI ≥25- < 30 kg/m2, obesity: adult BMI ≥30 kg/m2 [28]
4. Mann–Whitney U test for comparing groups. Monte Carlo sig. (2.tailed) confidence level 99 %
5. CI for mean change in the two groups: −0.40 (CI: −0.58 - -0.23) -0.39 (CI: −1.46 - 0.68)
6. BMI body mass index, LMS LMS curves/ LMS method: median (M), coefficient of variation (S) and skewness (L), SD standard deviation, SDS standard deviation score