Higher Incidence of Bulimia compared to Anorexia in Urbanised areas
Dec 1, 2006 - 3:04:15 PM
Urban life is a potential environmental risk factor for bulimia nervosa, but not for anorexia nervosa, according to a short report from The Netherlands in the December issue of the British Journal of Psychiatry.
The association between degree of urbanisation and a number of mental disorders is well established. Schizophrenia, psychosis and depression are known to occur more frequently in towns and cities.
In 1995 it was first reported that bulimia nervosa is associated with urban life. This study extends the research by adding data collected a decade later.
A network of about 63 general practitioners coordinated by the Netherlands Institute for Health Services Research recorded the number of newly diagnosed cases of anorexia and bulimia nervosa in their practices between 1985–1989 and 1995–1999.
The study population was divided into three levels of urbanisation: rural (20% or more of population engaged in agricultural labour), large cities (more than 100,000 inhabitants), and urbanised areas (all other areas).
During the 2 periods a total of 113 patients with anorexia (107 females and 6 males) and 110 with bulimia nervosa 107 females and 3 males) were newly diagnosed. Because there were so few male patients, the researchers analysed data from female patients only.
The incidence rate per year per 100,000 women-years for anorexia was 17.4 in rural areas, 20.2 in urbanised areas and 11.5 in large cities. Bulimia showed an incidence rate of 7.0 in rural areas, 16.7 in urbanised areas and 25.5 in large cities.
The main finding of the study was the association of bulimia incidence with degree of urbanisation in a ‘dose-response’ fashion. The incidence of bulimia was almost 2.5 times higher in urbanised areas than in rural areas, and 5 times higher in large cities than in rural areas. This is in contrast to the incidence of anorexia, which showed no association.
Anorexia and bulimia are thought to be closely related disorders e.g. core features of both are disturbed eating behaviours, and patients tend to move between diagnoses for the 2 disorders.
However, living in a large city seems to be strongly associated with the development of bulimia, but not with anorexia. The dose-response relationship of urbanisation and bulimia suggests causation.
Bulimia was relatively rare before 1970, but there was a sudden sharp rise in its incidence after 1980. Such fluctuations cannot be caused by changing genetic factors, as the time scale is too limited, suggesting a strong environmental influence.
The researchers explain the findings by 2 main hypotheses:
1. Migration. Adolescents tend to migrate to urban areas, where Dutch education facilities are usually located. These adolescents might already have developed bulimic symptoms but are ‘detected’ in the study in the more urbanised areas at an older age. The development of bulimia would then be independent of living in a large city. However, the researchers took account of age differences in their analyses, and the link with urbanisation remained.
2. Opportunity. In this hypothesis the higher incidence of bulimia in large cities is explained by the ability to obtain large amounts of food inconspicuously. In addition, the relative anonymity in large cities makes it easier to engage in secretive behaviour.
Other intra- and inter-personal factors may possibly account for the findings, and factors such as social cohesion, interpersonal trust and informal social control may also be involved, as they affect mental health.
In further studies, the residential history of participants should be taken into account, along with the time of onset of the bulimic symptoms.
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