Table 2.

Prevalence of thinness categories based on the IS cut-offs and the WHO cut-offs

Categories		Boys (n = 16,672)	Girls (n = 16,668)	Total (n = 33,340)
IS cut-offs
Grade 1	<18.5 kg/m2 *	22.5 (21.9 - 23.2)	20.3 (19.7 - 20.9)	21.4 (21.0 - 21.9)
Grade 2	<17.0 kg/m2 *	6.2 (5.8 - 6.6)	6.6 (6.2 - 7.0)	6.4 (6.2 - 6.7)
Grade 3	<16.0 kg/m2 *	1.6 (1.4 - 1.8)	2.3 (2.1 - 2.6)	2.0 (1.8 - 2.1)
WHO cut-offs
	<-1 SD	27.8 (27.1 - 28.5)	23.7 (23.0 - 24.3)	25.7 (25.2 - 26.2)
Thinness	<-2 SD	7.7 (7.3 - 8.1)	5.7 (5.4 - 6.1)	6.7 (6.4 - 7.0)
Severe thinness	<-3 SD	1.4 (1.2 - 1.6)	1.0 (0.9 - 1.2)	1.2 (1.1 - 1.3)

IS cut-offs: criteria from an international survey [7]; WHO cut-offs: criteria from the World Health Organization [8]; SD: standard deviation.

Results are expressed as percentage (95% confidence interval).

*at age 18 years