Increasing prevalence of obesity in primary school children: cohort study

Reports suggest that the prevalence of obesity among children is increasing. Reilly et al reported that, even by the age of 5, the prevalence of obesity was higher than that expected from the national standards¹ and that this persisted into the teenage years.²

Participants, methods, and results

From 1996 to 1999 an auxologist (JW) measured children in 10 primary schools in Leeds participating in a health promotion programme.³ Children in years 3 and 4 (age 7-9 years) were measured in July 1996 and again in July 1997 and 1998. These children were marginally more advantaged than average for Leeds, with 1-42% of pupils from ethnic minorities and 7-29% entitled to free school meals (a measure of social disadvantage).

Height was measured to 0.1 cm with a free standing Magnimeter stadiometer (Raven, Dunmow). Weights were recorded to 0.1 kg without shoes or jumpers. The mean of three triceps measurements was taken.⁴ Body mass index (weight (kg)/(height (m)²)) was calculated and converted to standard deviation scores using the revised 1990 reference standards⁵ and the Tanner Whitehouse (1975) standards for skinfold thickness.⁴ The following conventional cut-off pointswere applied: body mass index standard deviation score greater than 1.04 (85th centile) for overweight and greater than 1.64 (95th centile) for obesity. Using these definitions the expected percentages were 15% for overweight and 5% for obesity, relative to British children in 1990. Observed levels were compared with expected levels using χ² goodness of fit test.

All but 21 children agreed to participate. Overall, 608 children were measured in 1996, 540 in 1997, and 499 in 1998 (some of whom were not measured in 1997). In addition 86 new children joined the study in 1997 and 1998. In total 694 children were measured, resulting in 1762 measurements.

The table shows the proportion of children with body mass index and triceps measurements above the 85th and 95th centiles according to age. A significant increase in the proportion of overweight and obese children was observed in those aged 9, 10, and 11 years.

Comment

A noticeable increase in the prevalence of obesity has been observed such that one in five 9 year olds and one in three 11 year old girls are overweight. We collected new data on measurements of the skinfold at the triceps. Given the increase in the extent of body mass index these measures were surprisingly not significantly greater than those expected from the 1975 standards. Anecdotal evidence suggests that the 1975 standards were based on overweight children (T Coles, personal communication), and this may prove to be the simple explanation. However, a larger study is required to establish new references. The latest British growth standards were developed in 1990, but less than a decade later it has become evident that these standards no longer reflect the distribution of weight in British schoolchildren.

The cause for concern is twofold. Firstly, cohort studies show that obesity may track from childhood to adulthood, where morbidity is very evident. Secondly, obesity in adolescence is directly associated with increased morbidity and mortality in adult life independent of adult body weight. This study lends further support to reports that levels of obesity in Britain are increasing at an appreciable rate in primary school children, that the measures of skinfold at the triceps need to be revalidated, and that this major public health issue needs urgently addressing in young children.

Table.

Body mass index scores and triceps skinfold measures in Leeds primary school children. Values are numbers (percentages) unless stated otherwise

Age†	Girls							Boys
	7	8	9	10	11	Total		7	8	9	10	11	Total
Body mass index	n=22	n=162	n=261	n=230	n=112	n=787		n=30	n=192	n=320	n=280	n=153	n=975
Overweight	3 (14)	24 (15)	56 (22*)	53 (23**)	36 (32**)	172 (22**)		3 (10)	25 (13)	71 (22**)	70 (25**)	41 (27**)	210 (22**)
Obese	1 (5)	10 (6)	27 (10**)	33 (14**)	15 (13**)	86 (11**)		1 (3)	10 (5)	33 (10**)	38 (14**)	30 (20**)	112 (12**)
Triceps	n=22	n=160	n=257	n=231	n=112	n=782		n=29	n=190	n=318	n=280	n=153	n=970
Overweight	3 (14)	26 (16)	39 (15)	26 (11)	17 (15)	111 (14)		4 (14)	19 (10)	47 (15)	44 (16)	28 (18)	142 (15)
Obese	1 (5)	5 (3)	11 (4)	8 (4)	4 (4)	29 (4)		1 (4)	9 (5)	22 (7)	13 (5)	5 (3)	50 (5)

Prevalence of overweight and obesity is shown using definition of greater than 85th centile for overweight and greater than 95th centile for obese. 

Frequencies significantly different from expected values of 15% (overweight) and 5% (obesity) at ^*P<0.01, ^**P<0.001. 

^†Each year group was taken as year to next birthday (“seven” year olds included children aged 7 to less than 8 years).