Individual, family, and area predictors of BMI and BMI change in an adult Norwegian population: Findings from the HUNT study
Introduction
The increasing prevalence of obesity has been described as an epidemic process (James, 2008) and is now a major driver behind rises in the prevalence of certain chronic diseases and disabilities worldwide. Recent projections from the World Health Organisation (WHO) estimate that globally 1.6 billion adults were overweight and at least 400 million were obese in 2005, with these figures expected to grow to 2.3 billion and 700 million by 2015 (WHO, 2006). In Europe current trends are expected to give rise to 150 million obese adults by 2010 (Branca, Nikogosian, & Lobstein, 2007). The annual rate of increase in childhood obesity in this region is a particular cause for concern, with the current prevalence being over 10 times higher than in 1970 and with 15 million children expected to be obese by 2015 (Branca et al., 2007). Indeed, some have forecasted that youths of today may, on average, live less healthy and possibly even shorter lives than their parents (Olshansky et al., 2005).
In a recent WHO publication, Branca et al. (2007, p. xiii) state that “obesity presents Europe with an unprecedented public health challenge that has been underestimated, poorly assessed and not fully accepted as a strategic governmental problem with substantial economic implications”. The authors further note that the prevention of obesity requires innovative environmental approaches. The term “obesogenic environment” refers to the role environmental factors may play in determining food intake and physical activity, both important determinants of bodyweight (Jones, Bentham, Foster, Hillsdon, & Panter, 2007). Swinburn and colleagues have defined the concept as “the sum of influences that the surroundings, opportunities, or conditions of life have on promoting obesity in individuals or populations” (Swinburn, Egger, & Raza, 1999, p. 564). These authors have further described the environment in terms of micro and macro components, where micro-environments are defined as settings that influence peoples' interactions (e.g. home, school, workplace, and neighbourhood) which are themselves influenced by macro-environments (e.g. the education and health system, government policy and society's attitudes and beliefs).
The concept of an obesogenic environment is grounded in a systems perspective where health related behaviour is contextualised in the environment within which it takes place. The advancement of the concept has been driven by the development of ecological models which suggest that weight related behaviours, such as food intake and physical activity, arise as the result of the combined action of psychosocial, demographic, as well as physical environmental processes (Diez Roux, 2007, Van Dyck et al., 2009).
Numerous different environmental factors at various geographical scales have been put forward as potential determinants of overweight and obesity (Black & Macinko, 2008). There is some evidence of an effect of income inequality, with Pickett and colleagues (Pickett, Kelly, Brunner, Lobstein, & Wilkinson, 2005) finding a positive association between income inequality and rates of obesity in 21 developed countries, whilst Holtgrave and Crosby (2006) found higher levels of social capital in US states to be associated with a lower prevalence of obesity. At the neighbourhood level, many studies in the US (e.g. Diez-Roux et al., 2000, Janssen et al., 2006, Rundle et al., 2008), UK (e.g. Moon, Quarendon, Barnard, Twigg, & Blyth, 2007) and in Canada (e.g. Ross et al., 2007) have reported that high material deprivation levels are associated with elevated adult obesity prevalence.
A large amount of research evidence on the role of the physical environment is available. A recent review of predominantly US studies found that the majority reported an association between some aspect of the neighbourhood built environment and obesity, with associations with features such as the walkability of neighbourhoods and the accessibility of greenspaces being found (Papas et al., 2007). In addition to objectively measured features, the findings of a recent meta-analysis support the view that perceptions of the neighbourhood environment, such as those regarding safety and the accessibility of destinations, are also important (Duncan, Spence, & Mummery, 2005).
A contextual unit rarely acknowledged in the obesity literature is the family or household. Yet here is compelling evidence in support of interventions at the parent or family level in paediatric obesity research (Zeller et al., 2007). Parental obesity has a strong predictive power in the development of child and adolescent obesity, arguably with a genetic component, but there are also studies suggesting that there are indeed modifiable determinants operating at this contextual level (Krahnstoever Davison, Francis, & Birch, 2005). These could include the availability of foods, and the provision of familial social support for physical activity, and weight management practices.
There is strong evidence that the drivers of the epidemic are varied and operate via diverse pathways. Systems approaches (see Bailey, 1994) to exploring health behaviour causation can be useful in such situations, as they allow the outcomes of individual actions to be examined within the social and environmental contexts within which the individual operates. We adopt such a perspective in this study, where the aim is to contribute to an understanding of how environments may directly and indirectly affect behaviour and how such behaviour is ultimately expressed in terms of bodyweight. This is done firstly by quantifying variation in body mass index (BMI) and changes in BMI associated with individual, family, and area characteristics. Secondly we try to explain how the composition of individuals in families and areas may account for this variation. Finally we test how contextual features like family and area socioeconomic status, and area deprivation and social capital may explain variability in the outcomes not associated with characteristics of individuals. The research is longitudinal, utilising anthropometric height and weight measurements from two time points amongst a large and settled adult population from the county of Nord-Trøndelag in Norway.
Section snippets
Data sources
The Nord-Trøndelag Health Study (HUNT) is one of the world's largest population health surveys. The first wave (HUNT 1) was carried out in 1984–1986. All residents of Nord-Trøndelag County in Norway aged 20 or above were invited to participate in the study which included a physical examination and self-completed questionnaires. Questionnaire 1 was attached to the invitation letter, and 74,977 (88.1%) of the 85,100 eligible persons completed and returned it when they attended. Of these, 74,332
Results
Table 1 describes the characteristics of the sample and the contextual variables. Mean BMI increased by nearly 2 kg/m2 during the 11 years of follow-up, and the standard deviation increased from 3.47 to 3.92. Mean age at baseline was 43 years. Males and females are equally represented and the majority were married. The variables measuring individual SES indicate that most individuals reported working in manual occupations and had a low educational level. Nevertheless, the majority did not
Discussion
In this study we have examined the correlates of BMI and BMI change in a large longitudinal sample of adult individuals. We found that both outcomes were associated with individual characteristics, with higher BMI most often found amongst males, unmarried participants, non-smokers, those of lower education and those undertaking physically demanding work but participating in less physical activity outside work. The characteristics of those in the sample exhibiting higher BMI gain were rather
Conclusion
In conclusion, we found that a statistically significant proportion of the variance in BMI and BMI change can be attributed to families, in addition to the individual. We were able to quantify the family components that determined our outcomes but insight from elsewhere does suggest that processes governing physical activity and nutrition in families are extremely complex (Kegler, Escoffery, Alcantara, Ballard, & Glanz, 2008). The small amounts of variance attributable to the ward and
Acknowledgements
The Nord-Trøndelag Health Study (The HUNT Study) is a collaboration between HUNT Research Centre (Faculty of Medicine, Norwegian University of Science and Technology NTNU), Nord-Trøndelag County Council and The Norwegian Institute of Public Health. The present study was supported by grants from the Faculty of Social Sciences and Technology Management, Norwegian University of Science and Technology and was carried out in 2009. The authors thank Stig H. Jørgensen, Steinar Krokstad, Johan Håkon
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