Table 4 Relationship between five factors and OSI for boys

Body mass index (kg/m²)

 −18.4

419 (58.5)

2.53 ± 0.24

1,008 (52.3)

2.59 ± 0.23

593 (38.4)

2.66 ± 0.26

209 (26.6)

2.72 ± 0.30

 18.5–24.9

264 (36.9)

2.64 ± 0.25

821 (42.6)

2.71 ± 0.29

866 (56.1)

2.85 ± 0.30

509 (64.7)

2.92 ± 0.35

 25.0–

33 (4.6)

2.79 ± 0.44

97 (5.0)

2.82 ± 0.29

86 (5.6)

2.97 ± 0.35

69 (8.8)

3.03 ± 0.32

 P value*

<0.001

<0.001

<0.001

<0.001

Exercise habits

 None

45 (6.3)

2.57 ± 0.29

118 (6.1)

2.57 ± 0.30

142 (9.2)

2.68 ± 0.31

74 (9.4)

2.72 ± 0.29

 PS or current

215 (30.0)

2.53 ± 0.23

473 (24.6)

2.61 ± 0.23

398 (25.8)

2.78 ± 0.33

212 (26.9)

2.86 ± 0.34

 PS and current

456 (63.7)

2.60 ± 0.26

1,335 (69.3)

2.67 ± 0.27

1,005 (65.0)

2.80 ± 0.29

501 (63.7)

2.90 ± 0.35

 P value*

0.006

<0.001

<0.001

<0.001

Milk intake per day during PS (mL)

 <200

257 (35.9)

2.55 ± 0.20

705 (36.6)

2.63 ± 0.26

570 (36.9)

2.74 ± 0.31

296 (37.6)

2.81 ± 0.33

 200–400

289 (40.4)

2.59 ± 0.27

707 (36.7)

2.64 ± 0.26

529 (34.2)

2.80 ± 0.30

280 (35.6)

2.88 ± 0.33

 >400

170 (23.7)

2.62 ± 0.29

514 (26.7)

2.69 ± 0.28

446 (28.9)

2.83 ± 0.31

211 (26.8)

2.94 ± 0.36

 P value*

0.023

<0.001

<0.001

<0.001

Current milk intake per day (mL)

 <200

272 (38.0)

2.57 ± 0.24

751 (39.0)

2.62 ± 0.26

609 (39.4)

2.74 ± 0.30

299 (38.0)

2.83 ± 0.36

 200–400

291 (40.6)

2.58 ± 0.25

721 (37.4)

2.65 ± 0.26

547 (35.4)

2.80 ± 0.30

285 (36.2)

2.88 ± 0.32

 >400

153 (21.4)

2.60 ± 0.28

454 (23.6)

2.69 ± 0.28

389 (25.2)

2.82 ± 0.31

203 (25.8)

2.91 ± 0.33

 P value*

0.408

<0.001

<0.001

0.024

Bone fracture during the preceding year

 Yes

81 (11.3)

2.56 ± 0.21

167 (8.7)

2.64 ± 0.28

131 (8.5)

2.77 ± 0.31

58 (7.4)

2.92 ± 0.33

 No

635 (88.7)

2.58 ± 0.26

1,759 (91.3)

2.65 ± 0.26

1,414 (91.5)

2.78 ± 0.31

729 (92.6)

2.87 ± 0.34

 P value**

0.351

0.571

0.557

0.250