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Body size (various ages)


A healthy body size is recognised as important for good health and wellbeing, with evidence showing that obese children and adults are at greater risk of short- and long-term health consequences (Ministry of Health 2008).

Body mass index (BMI) provides a useful population-level indicator of excess body weight. It is a measure of weight adjusted for height and is calculated by dividing weight in kilograms by the square of height in metres (kg/m2). BMI is used internationally to classify underweight, overweight and obesity.

It should be noted that the BMI provides a crude measure and does not distinguish between weight associated with muscle and weight associated with fat. However, it does provide a good estimate of increased risk of health conditions associated with obesity (World Health Organization 2008).

To comply with current international practice, the same BMI cut-off points are now used for all ethnic groups (please refer to the online 2006/07 New Zealand Health Survey body size technical report for more information at: http://www.moh.govt.nz/moh.nsf/indexmh/portrait-of-health.

Therefore, data presented in this edition of the chart book should not be compared with those presented in the first edition, which used ethnic-specific cut-off points to analyse body size (Ministry of Health 2006).

Table 10: International cut-off points for adults aged 18 years and over
ClassificationBMI score kg/m2Risk of health conditions
Underweight< 18.5Low risk
Overweight25.00-29.99Increased risk
Obese> 30.0Substantially increased risk
Source: Ministry of Health 2008

Note: Only includes health conditions associated with increasing BMI.

Details on the classification of overweight and obesity in children can be found in Cole et al (2000, 2007).

There is an association between BMI and health risk (Asia Pacific Cohort Studies Collaboration 2004), and therefore, it is useful to have some information about the BMI distribution rather than relying on BMI cut-offs alone. For this reason, this chart book presents data on BMI percentiles as well as underweight, overweight and obesity. For example, a 10th percentile BMI of 22 means that 10 percent of the population have a BMI of 22 or less; a 50th percentile BMI of 28 means that 50 percent of the population have a BMI of 28 or less.
How to interpret results - tables

Table 11: Body size indicators

Indicator
Māori
non-Māori
Males
Females
Total
Males
Females
Total
Children
Overweight, 5-14 years, 2006-07, percent 1,2
23.7
(20.0–27.3)
25.6
(20.1–31.1)



24.6
(21.3–27.9)
19.1
(15.9–22.2)
18.5
(15.7–21.3)
18.8
(16.6–21.1)
Obese, 5-14 years, 2006-07, percent1,2
12.0
(9.0–15.0)




13.3
(9.6–16.9)
12.6
(10.4–14.9)
6.9
(5.5–8.4)
7.3
(5.7–8.9)
7.1
(6.0–8.2)
BMI 10th percentile 5-14 years, 2006-07, BMI value 1,2
15.6
(15.3–15.9)




15.3
(14.9–15.7)
15.4
(15.2–15.7)
15.4
(15.2–15.7)
15.1
(14.8–15.3)
15.3
(15.1–15.5)
BMI 50th percentile, 5-14 years, 2006-07, BMI value 1,2
18.6
(18.1–19.0)




18.9
(18.5–19.2)
18.8
(18.5–19.1)
18.0
(17.7–18.3)
18.1
(17.8–18.4)
18.0
(17.8–18.3)
BMI 90th percentile 5-14 years, 2006-07, BMI value, 1,2
25.1
(24.0–26.2)




26.7
(24.9–28.5)
25.8
(24.8–26.8)
23.6
(22.9–24.2)
24.1
(23.4–24.8)
24.0
(23.5–24.4)
Adults
Underweight, 15+ years, 2006-07 percent 1,2
0.4
(0.1–0.9)
1.3
(0.6–2.3)
0.8
(0.5–1.4)
1.2
(0.8–1.7)
1.5
(1.0–2.0)
1.3
(1.0–1.7)
Overweight, 15+ years, 2006-07, percent 1,2
33.9
(30.4–37.5)
29.3
(26.3–32.3)
31.5
(29.5–33.6)
42.9
(41.3–44.5)
30.7
(29.1–32.2)
36.8
(35.8–37.8)
Obese, 15+years, 2006-07, percent 1,2
40.6
(37.1–44.0)
41.6
(38.6–44.6)
41.1
(39.2–43.1)
24.1
(22.6–25.7)
25.0
(23.4–26.5)
24.6
(23.5–25.6)
BMI 10th percentile, 15+ years, 2006-07, BMI value 1,2
22.4
(21.9–22.9)
21.4
(20.9–21.9)
22.0
(21.6–22.3)
21.7
(21.4–22.0)
20.5
(20.4–20.7)
21.0
(20.8–21.1)
BMI 50th percentile, 15+ years, 2006-07, BMI value 1,2
28.3
(27.7–29.0)
28.2
(27.6–28.8)
28.3
(27.9–28.7)
26.9
(26.7–27.1)
25.7
(25.5–25.9)
26.4
(26.2–26.5)
BMI 90th percentile, 15+ years, 2006-07, BMI value 1,2
37.2
(36.2–38.3)
39.6
(38.5–40.7)
38.3
(37.7–38.9)
33.3
(33.0–33.7)
35.1
(34.5–35.6)
34.0
(33.7–34.3)
Source: 2006/07 New Zealand Health Survey
Notes:
  1. Age standardised to 2001 Census total Māori population.
  2. Prioritised Māori ethnic group – see Ngā Tapuae me ngā Raraunga: Methods and Data Sources’ for further information.

The table above shows that for children aged 5–14 years, Māori and non-Māori boys had a similar prevalence of overweight, but Māori girls were nearly 1.4 times more likely to be overweight than non-Māori girls (RR 1.38, CI 1.02–1.74). Overall, the prevalence of obesity in Māori children was more than one-and-a-half times greater than that in non-Māori children (RR 1.77, CI 1.32–2.22).

Both the BMI 10th and 50th percentiles for Māori and non-Māori children were similar; however, Māori children had a slightly higher BMI 90th percentile.

Māori adults were slightly less likely than non-Māori adults to be overweight (RR 0.86, CI 0.80– 0.92). However, Māori adults were more than one-and-a-half times more likely to be obese than non-Māori (RR 1.67, CI 1.56–1.78). Māori adults had higher 10th, 50th and 90th percentiles for BMI than non-Māori adults.

Page last updated: 7 September 2010

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