Prevalence and Recent Trends in Overweight,Obesity,and Severe Obesity among New Zealand Adolescents

Abstract

Background:

Around the world, there have been numerous reports of a leveling of the prevalence of obesity. Given that New Zealand has among the highest rates of child and adult obesity in the Organization for Economic Cooperation and Development (OECD), the aim of the current study was to document the prevalence of, and recent trends in, overweight, obesity, and severe obesity among adolescents in New Zealand.

Methods:

Data were collected as part of two nationally representative surveys in 2007 and 2012. In both surveys, a nationally representative group of students was selected to participate in the health and well-being surveys from a nationally representative sample of secondary schools. Across the two surveys, more than 17,000 students participated in the survey, which also included measured heights and weights.

Results:

In 2012, nearly 40% of adolescents in New Zealand were overweight, obese, or severely obese. Between 2007 and 2012, there were no decreases in the prevalence of obesity for the general population or any demographic subgroup. However, the prevalence of obesity and severe obesity for Pacific young people increased significantly. Of note, the prevalence of severe obesity for Pacific young people increased from 9% in 2007 to 14% in 2012.

Conclusions:

Findings from the current study indicate the need for an urgent investment in obesity prevention, particularly to address the growing inequalities in obesity for Pacific young people.

Introduction

After several decades of a steady increase in obesity, recent data from the United States has suggested that the prevalence of obesity may be starting to plateau.^1,2 However, these findings were not uniform across the population given that men and adolescent boys appeared to still be experiencing increases in obesity through 2010. Moreover, there have been no notable movements toward decreasing ethnic inequalities in the burden of obesity.

New Zealand has the third highest rates of obesity in the OECD (Organization for Economic Cooperation and Development)³ for both adults and children. Nearly one third (30%) of adults in New Zealand are obese⁴; this is similar to the prevalence of obesity in Australia (28%)⁵ and the United States (35%).⁶ Data on adolescent obesity in New Zealand are extremely limited owing to the fact that the only frequent and routine health survey conducted includes relatively small numbers of adolescents. A small regional study of adolescent obesity in New Zealand found that the prevalence of obesity increased markedly from 19% to 31% between 1997 and 2005.⁷ Obesity during adolescence is a significant indicator given that approximately 90% of adolescents with obesity remain obese into adulthood.⁸

The aims of the current study are to document the prevalence of, and recent trends in, overweight, obesity, and severe obesity among two nationally representative samples of adolescents in New Zealand and determine whether changes in obesity are similar for all sociodemographic subgroups in the population.

Methods

Data for the current study were collected as part of two nationally representative surveys of the health and well-being of high school students in New Zealand in 2007 (Youth'07) and 2012 (Youth'12).^9,10 Both surveys adopted a two-stage sampling procedure where first schools, then students within schools, were randomly selected for participation. In 2007, 9107 students from 96 schools participated, reflecting response rates for schools and students at 84% and 74%, respectively. In 2012, 8500 students from 91 schools participated, reflecting response rates for schools and students at 73% and 68%, respectively.

In both surveys, consent for participation was obtained from school principals on behalf of the boards of trustees. In both surveys, students and their parents were provided with information sheets about the survey. Students consented themselves to participate in the survey. The University of Auckland Human Subject Ethics Committee granted ethical approval for both surveys.

All data collection took place at school, during the school day. All data were collected anonymously. Students were assigned a unique identifier, which was they used to log into the survey and for recording their height, weight, and residential meshblock. Students were weighed and measured in light clothing without shoes by trained research staff using digital scales and portable stadiometers. BMI was calculated as weight (kilograms) / height (meters).² Overweight, obesity, and severe obesity were defined using the criteria recommended by the International Obesity Task Force.^11,12 BMI cutpoints for overweight, obesity, and severe obesity are made by age and sex and are based on pooled international data. The cutpoints correspond to an adult BMI of 25 (overweight), 30 (obesity), and 35 (severe obesity).

Demographic and socioeconomic data were measured by self-report. Ethnicity was assessed using the standard measures developed for the New Zealand census,¹³ where participants can select all of the ethnic groups that they identify with. To facilitate statistical analyses, discrete ethnic populations were created using a prioritization method, where students were assigned to one ethnic group in the following order: Māori (Indigenous people of New Zealand); Pacific (includes Samoa, Tonga, Cook Island, and other Pacific Islands); Asian; other ethnicity; and European.¹³ In both surveys, students orally provided their residential address, to identify and record their geographical meshblock of residence. This meshblock is a small area of approximately 100 residents. The meshblock was then linked to the New Zealand Index of Deprivation to measure area-level deprivation¹⁴ and also used to determine urban/rural residence. Household poverty was assessed by the presence of any two of the following eight indicators: household food insecurity (often/all the time); moving homes frequently (two or more times in past year); not having a working car at home; not having a telephone at home; not having a computer at home; overcrowding (more than 2 people per bedroom); both parents unemployed; and use of rooms other than bedrooms for sleeping (e.g., living room and garage).

Statistical Analysis

All analyses were conducted using SAS software (SAS Institute Inc., Cary, NC) and accounted for the weighting and clustering of the data. The prevalence of overweight, obesity, and severe obesity were generated to describe the population (and demographic subgroups) in both 2007 and 2012. To determine differences in the prevalence of overweight, obesity, and severe obesity between the two time points, logistic regression models were generated. Last, regression models, which included interaction terms between variables of interest, were created to determine whether changes in body size over time were moderated by any demographic or socioeconomic variables. All differences were considered statistically significant at p < 0.05.

Results

In 2012, nearly 40% of adolescents in secondary school in New Zealand were overweight, obese, or severely obese (Table 1). There were few or no differences in the prevalence of obesity by age, sex, or urban/rural residence, but there were some notable differences by ethnicity and socioeconomic indicators. Prevalence of obesity (plus severe obesity) was higher among students living in high deprivation areas (22%) and for students living with poverty (26%), compared with more-affluent students (6% for students in low deprivation areas and 10% for students not living with poverty). Approximately 67% of Pacific students met the criteria for overweight, obesity, or severe obesity, compared with 44% of Maori students, 29% of European students, and 23% of Asian students.

Table 1.

Trends in BMI and Overweight, Obesity, and Severe Obesity by Sociodemographic Variables: 2007–2012

		Overweight		Obese		Severe obesity		p value	p value for interaction³
	n	%	CI	%	CI	%	CI
Total
2007	8806	24.2	(22.7, 25.6)	7.8	(6.8, 8.8)	2.5	(1.9, 3.1)
2012	8372	24.1	(22.8, 25.4)	8.9	(7.5, 10.2)	3.7	(2.5, 5.0)	0.23
Sex
Male
2007	4808	23.6	(21.9, 25.3)	8.1	(7.0, 9.2)	2.6	(2.0, 3.3)
2012	3853	23.4	(21.9, 24.8)	8.9	(7.5, 10.3)	3.2	(2.1, 4.3)	0.52
Female
2007	3991	24.8	(22.7, 26.9)	7.5	(6.1, 8.9)	2.4	(1.5, 3.2)
2012	4516	24.7	(22.8, 26.5)	8.9	(7.0, 10.7)	4.2	(2.5, 6.0)	0.20	0.38
Age, years
13 and under
2007	1785	26.5	(24.2, 28.8)	8.5	(6.7, 10.3)	2.6	(1.7, 3.5)
2012	1806	25.0	(22.6, 27.4)	9.8	(7.7, 11.8)	3.0	(2.0, 3.9)	0.80
14
2007	2020	23.6	(21.5, 25.8)	7.6	(6.4, 8.9)	2.2	(1.2, 3.2)
2012	1866	25.2	(22.8, 27.7)	8.6	(6.9, 10.3)	3.8	(2.0, 5.6)	0.11
15
2007	1929	23.8	(21.6, 26.1)	8.6	(6.9, 10.3)	2.6	(1.8, 3.4)
2012	1738	25.4	(23.3, 27.5)	8.5	(6.7, 10.3)	4.1	(2.6, 5.5)	0.25
16
2007	1683	22.5	(20.0, 25.0)	7.0	(5.6, 8.4)	2.5	(1.7, 3.3)
2012	1553	21.4	(19.2, 23.6)	9.9	(8.1, 11.7)	3.8	(2.1, 5.6)	0.13
17 and older
2007	1382	24.4	(21.9, 26.9)	7.0	(5.6, 8.4)	2.8	(1.7, 3.8)
2012	1398	22.6	(20.2, 25.0)	7.4	(5.9, 9.0)	4.1	(2.4, 5.9)	0.83	0.27
Ethnicity
Asian
2007	1102	20.8	(18.7, 23.0)	4.3	(3.0, 5.5)	1.0	(0.3, 1.7)
2012	1038	17.1	(14.5, 19.6)	5.4	(3.9, 6.9)	0.8	(0.2, 1.4)	0.22
European/other
2007	5178	21.2	(19.8, 22.7)	5.6	(4.9, 6.3)	1.1	(0.7, 1.4)
2012	4483	22.3	(20.9, 23.7)	5.2	(4.4, 6.0)	1.4	(1.1, 1.7)	0.45
Māori
2007	1638	30.3	(27.6, 33.0)	11.6	(9.8, 13.4)	4.6	(3.4, 5.9)
2012	1661	26.7	(24.7, 28.7)	12.7	(11.1, 14.2)	4.6	(3.3, 5.9)	0.42
Pacific
2007	872	34.4	(30.5, 38.4)	18.3	(15.9, 20.7)	9.0	(6.7, 11.3)
2012	1180	33.1	(30.3, 35.8)	20.4	(18.1, 22.7)	14.0	(10.7, 17.3)	0.02	0.02
Small area deprivation
Low deprivation
2007	3182	21.0	(19.1, 22.9)	4.9	(4.0, 5.8)	0.8	(0.4, 1.2)
2012	2436	20.6	(18.6, 22.6)	5.6	(4.5, 6.7)	0.7	(0.4, 1.1)	0.81
Middle levels of deprivation
2007	3360	24.0	(22.3, 25.7)	7.2	(6.3, 8.1)	2.1	(1.6, 2.6)
2012	3077	23.6	(22.2, 25.0)	7.6	(6.6, 8.6)	2.2	(1.6, 2.7)	0.88
High deprivation
2007	2214	29.0	(26.5, 31.5)	12.9	(11.0, 14.8)	5.7	(4.2, 7.1)
2012	2708	28.1	(25.9, 30.3)	13.4	(10.9, 15.9)	8.4	(6.0, 10.7)	0.37	0.68
City
Major city
2007	6164	23.7	(21.9, 25.4)	7.9	(6.6, 9.2)	2.7	(1.8, 3.5)
2012	6215	24.2	(22.6, 25.7)	9.1	(7.4, 10.8)	4.3	(2.6, 5.9)	0.20
Small city
2007	1198	25.0	(22.7, 27.3)	8.0	(6.4, 9.6)	3.2	(2.0, 4.4)
2012	946	26.5	(23.6, 29.4)	9.2	(7.6, 10.8)	2.8	(1.6, 3.9)	0.41
Rural
2007	1414	25.5	(22.7, 28.3)	7.1	(5.7, 8.4)	1.3	(0.7, 1.9)
2012	1228	21.8	(19.0, 24.5)	7.4	(5.8, 9.0)	1.6	(0.9, 2.4)	0.22	0.11
Household poverty
Yes
2007	1034	32.1	(29.1, 35.2)	13.5	(10.8, 16.2)	5.8	(4.2, 7.3)
2012	1104	29.3	(26.6, 32.0)	16.5	(13.7, 19.3)	9.5	(7.0, 12.0)	0.10
No
2007	7772	23.1	(21.7, 24.5)	7.1	(6.2, 7.9)	2.1	(1.6, 2.6)
2012	7268	23.3	(22.0, 24.5)	7.7	(6.7, 8.8)	2.9	(1.9, 3.8)	0.27	0.15

Analyses controlling for age and sex.

Analyses included interaction term (year^*sociodemographic variable), controlling for age and sex.

Analyses included interaction term (year^*sociodemographic variable).

CI, confidence interval.

Between 2007 and 2012, there were no changes in prevalence of overweight, obesity, or severe obesity for the general population. However, prevalence of obesity and severe obesity increased for Pacific young people from 27% in 2007 to 34% in 2012 (p = 0.02). Of note, prevalence of severe obesity alone for Pacific young people increased from 9% in 2007 to 14% in 2012. There were no other increases in prevalence of overweight, obesity, or severe obesity for any subgroup of the population.

Discussion

The current study aimed to document timely data on the prevalence of overweight, obesity, and severe obesity among adolescents in New Zealand and determine whether there have been any recent improvements in adolescent obesity for the general population or any demographic subgroup of the population.

The prevalence of overweight, obesity, and severe obesity among adolescents in New Zealand remained high through 2012 at just below 40%. Moreover, there have been no improvements in obesity across the general population or for any demographic subgroup between 2007 and 2012, and the prevalence of obesity and severe obesity was significantly worse for Pacific adolescents. Of particular concern, prevalence of severe obesity among Pacific young people increased by more than 50% between 2007 and 2012.

Our findings expand on what was reported during the last national health surveys conducted across the whole population of New Zealand. The New Zealand Health Survey found the prevalence of obesity in children (2–14 years) increased from 8% to 10% between 2006–2007 and 2011–2012, but this was only significant for boys. For young adults (15–24 years), prevalence of obesity increased from 14% to 20% between the two surveys.^15,16 Moreover, prevalence of obesity (excluding overweight) for Pacific people in New Zealand remained high in the 2011–2012 health survey, with 25% of Pacific children (ages 2–14) and 67% of Pacific adults experiencing obesity.

Comprehensive strategies and leadership are needed to address childhood obesity. The Robert Wood Johnson Foundation reported significant reductions in child obesity across several cities in the United States, all of which have enacted comprehensive policies to address childhood obesity.¹⁷ Findings presented in the current study generally reflect the lack of government resource directed at obesity prevention over the past 6 years.¹⁸ In 2008, New Zealand experienced a change in government leadership and major obesity prevention initiatives were either dismissed or lost funding.¹⁸ One such program, Healthy Eating Healthy Action,¹⁹ provided support and resources for community-based initiatives to reduce ethnic inequalities in obesity. Programs to reduce inequalities in obesity are particularly important for New Zealand given that Pacific people are over-represented on multiple indicators of poverty and deprivation, resulting in multiple indicators of poor health.²⁰

Conclusions

In summary, since 2007 the burden of obesity among adolescents in New Zealand has not improved, and for Pacific young people has become significantly worse. Political leadership, advocacy, significant improvements to the food environment, increased opportunities for physical activity, and culturally relevant and effective weight management programs will be needed to reduce the high prevalence of obesity and curb the growing inequalities for Pacific populations.

Footnotes

Acknowledgments

Funding for the current study was provided by a consortium of eight government agencies: the Ministry of Youth Development; the Ministry of Social Development; the Ministry of Education; the Ministry of Health; the Ministry of Justice; the Department of Labor; the Health Promotion Agency; and the Families Commission.

Author Disclosure Statement

No competing financial interests exist.

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