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Table 1 Characteristics of the 12-year-old study population

From: BMI, waist circumference at 8 and 12 years of age and FVC and FEV1 at 12 years of age; the PIAMA birth cohort study

  Girls n = 655 Boys n = 633
  Mean (sd) Mean (sd)
Age (year)* 12.7 (0.4) 12.6 (0.4)
Waist circumference (cm)* 66.0 (6.5) 66.9 (6.9)
BMI (kg/m2)* 18.9 (2.7) 18.6 (2.7)
Height (cm)* 160.6 (2.7) 159.2 (7.9)
Sitting height (cm)* 82.8 (4.1) 81.0 (3.7)
Sitting height/height ratio* 0.52 (0.01) 0.51 (0.01)
FEV1 (L) 2.73 (0.4) 2.69 (0.4)
FVC (L)* 3.19 (0.5) 3.25 (0.5)
FEV1/FVC ratio* 0.86 (0.1) 0.83 (0.1)
  n/N (%) n/N (%)
Asthma symptoms 74/636 (11.6) 93/616 (15.1)
Frequent asthma symptoms 21/636 (3.3) 33/616 (5.4)
Sensitization* 175/550 (31.8) 254/562 (45.2)
Allergic mother 219/655 (33.4) 208/633 (32.9)
Overweight§* 80/655 (12.2) 83/633 (13.1)
Obesity§* 4/655 (0.6) 7/633 (1.1)
BMI category 8 and 12 years£   
 Normal-normal 418/563 (74.3) 393/527 (74.6)
 High-normal 22/563 (3.9) 20/527 (3.8)
 Normal-high 15/563 (2.7) 16/527 (3.0)
 High-high 34/563 (6.0) 32/527 (6.1)
Waist circumference category 8 and 12 years£   
 Normal-normal 403/563 (71.6) 381/527 (72.3)
 High-normal 27/563 (4.8) 22/527 (4.2)
 Normal-high 21/563 (3.7) 24/527 (4.6)
 High-high 29/563 (5.2) 26/527 (4.9)
Maternal educational level   
 Low 106/655 (16.2) 119/633 (18.8)
 Intermediate 284/655 (43.5) 246/633 (38.9)
 High 263/655 (40.3) 268/633 (42.3)
Use of asthma medication within 48 hours before lung function measurement 20/513 (3.9) 31/517 (6.0)
Having a cold during lung function measurement 52/510 (10.2) 44/518 (8.5)
Wheezing in the past year 25/641 (3.9) 37/617 (6.0)
  1. *P < .05 difference between boys and girls.
  2. In the PIAMA study, ‘asthma symptoms’ are defined as at least 1 attack of wheeze, and/or at least 1 episode of dyspnoea and/or a prescription of inhaled corticosteroids in the last 12 months.
  3. In the PIAMA study, ‘frequent asthma symptoms’ are defined as having asthma symptoms and ≥4 attacks of wheeze or ≥4 attacks of dyspnoea in the last 12 months.
  4. §Overweight and obesity were defined according to standard international definitions, specified for age and gender [23].
  5. £Three BMI sd-score categories and three WC sd-score categories were defined: 1) below the 10th percentile, 2) above the 90th percentile and 3) between the 10th and 90th percentile, which we call ‘normal’. The percentiles were based on the distribution for boys and girls separately, and at age 8 and 12 years separately. Using the ‘normal’ and ‘high’ categories four new categories were defined for BMI and WC separately.