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

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

	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)

*P < .05 difference between boys and girls.
^†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.
^‡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.
^§Overweight and obesity were defined according to standard international definitions, specified for age and gender [23].
^£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.

ISSN: 1471-2466