I typically don’t report on scholarly studies in this blog but recently came across a nicely designed study that makes a larger point—that the links between health and place are complex. Fei Xu, JieQuan Li, YaQiong Liang, ZhiYong Wang, Xin Hong, Robert S Ware, Eva Leslie, Takemi Sugiyama, and Neville Owen have produced a report on the Nanjing High School Students’ Health Survey, published in the Journal of Epidemiology and Community Health in 2010 (64, 1017-1021, http://jech.bmj.com/content/64/11/1017). Titled: “Residential density and adolescent overweight in a rapidly urbanising region of mainland China” the study used data collected from 2,375 adolescents in 2004 to examine the relationship between (large-scale) district level densities and weight.
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| New high rise behind village residences in suburban Shanghai, 2010 |
Densities are reported per square kilometer but in range from 5 persons per hectare to 307. The study divided the sample into high, medium, low density residents. Youth in the middle and higher density areas (that is over > 35 person per hectare) were roughly twice as likely to be overweight.
The relationship was reduced a bit but still significant after controlling for TV time, study time, recreation, age, gender, and parents education. Physical activity data came from self reports through a version of the International Physical Activity Questionnaire (IPAQ) that only asked about some kinds of activities. Given a lack of data on overall physical activity and food intake the authors speculate on a number of reasons for this difference e.g. youth in higher density and potentially higher income areas eating more, higher density areas having less recreational space, or (and here I am paraphrasing quite loosely) that higher density areas may just be too convenient with too much internet access so youth don’t have to expend much energy getting places. The high densities in China are also quite high compared with the US and Australia in particular, where much research has been done. They are also increasing rapidly—the authors report overall densities in Nanjing, presumably including some rural districts, increasing from 14 persons per hectare in 1997 to 23 in 2007.
The study is interesting because in many studies of adults, those in higher densities walk more for transportation (though they may not walk more overall) and some find they are thinner (though not all studies measure this or find it to be true, including my own). In this study of youth, with a large group and fairly good measures, those in higher densities are chubbier. While it is important not to make too much of one study, this is yet another example of the complexity of the relationship between health and place, and the importance of social factors.