Researchers have examined large datasets from Denmark to determine how genetic and environmental factors interact to affect whether people develop anorexia nervosa. One researcher says that it is important to understand that anorexia nervosa is not a voluntary eating disorder, since it results from a complex interaction between genetics and the environmental conditions people experience.
Anorexia nervosa is a serious eating disorder that disproportionately affects young women, and researchers do not fully understand the causes behind it.
Anorexia nervosa does not mean voluntarily choosing not to eat, and both genetic and environmental factors contribute to its development.
For example, researchers have identified eight genome-wide risk loci that predispose to inheriting genetic susceptibility to anorexia nervosa. Researchers also know that environmental factors can affect the risk of anorexia nervosa, such as being born by caesarean section.
Several small studies have investigated how various factors influence an individual’s risk of anorexia nervosa, but recently researchers have investigated these factors in a large dataset from Denmark. The study shows how genetic susceptibility and environmental factors influence the risk of developing anorexia nervosa but also that many diverse pathways can lead to this disorder.
“We hope that our research can help in removing the stigma associated with having an eating disorder. Many people still perceive the causes of anorexia nervosa incorrectly, and this study aimed to identify the underlying mechanisms,” explains a lead researcher behind the study, Zeynep Yilmaz, Senior Researcher, National Centre for Register-based Research, Aarhus University, Denmark.
The research has been published in Psychological Medicine.
Data on more than 50,000 people in Denmark
The researchers aimed to contribute to this field with a large population study and therefore analysed cohorts of people with eating disorders in Denmark, which has very complete data on the presence of this diagnosis based on the population of an entire country.
The datasets contained data on 7,003 individuals with an anorexia nervosa diagnosis born in Denmark between 1981 to 2008 and 45,229 without a registered anorexia nervosa diagnosis. The researchers also included 22 previously identified anorexia nervosa risk factors from the registries.
Based on the data, the researchers calculated the polygenic risk score associated with anorexia nervosa – estimating an individual’s risk for developing a specific disease based on their genetic susceptibility.
The researchers could thus determine how the genetic susceptibility for anorexia nervosa was associated with environmental risk factors.
“Our hope was that the registry data would enable us to better understand the interaction between the genetic and environmental factors associated with anorexia nervosa,” says Zeynep Yilmaz.
Diverse factors associated with genetic susceptibility for anorexia nervosa
The results indicate that increased genetic susceptibility is associated with specific environmental risks.
For instance, increased genetic susceptibility for anorexia nervosa is often present among girls and women born to mothers younger than 20 years or older than 25 years, those whose mothers experienced a urinary tract infection during pregnancy and individuals born through caesarean section.
Parental socioeconomic factors, urban versus rural residence and history of mental disorder were also associated with the genetic susceptibility for anorexia nervosa.
According to Zeynep Yilmaz, this indicates that the same genetic susceptibility can influence both anorexia nervosa and environmental or lifestyle factors, or alternatively, environmental factors can influence other factors, including the risk of anorexia nervosa.
“Some factors may also increase the likelihood of detecting anorexia nervosa. For example, the probability of being diagnosed with anorexia nervosa may be greater for individuals living in urban areas because they have easier access to the healthcare system and specialist physicians than people living in the countryside,” she adds.
The researchers also adjusted the data for the genetic susceptibility to determine whether the other factors were still associated with an increased risk of anorexia nervosa, and they found that this was indeed the case.
Leading to more research
According to Zeynep Yilmaz, the results will not be immediately relevant for treating people with anorexia nervosa but may help to inform future research.
“We are on a journey towards understanding how diverse risk factors lead to developing anorexia nervosa. However, there is currently far too little knowledge about how anorexia nervosa affects men, since the vast majority of data are on women with anorexia nervosa. The most important thing, however, is that there is not just one pathway to developing anorexia nervosa. It is important to point out to individuals who develop anorexia nervosa that it is neither their fault nor that of their parents,” concludes Zeynep Yilmaz.
“Interplay of polygenic liability with birth-related, somatic, and psychosocial factors in anorexia nervosa risk: a nationwide study” has been published in Psychological Medicine. The research was supported by the Lundbeck Foundation, Aarhus University, Aarhus University Hospital, the University of Copenhagen, Copenhagen University Hospital, the Klarman Family Foundation, the United States National Institute of Mental Health, Independent Research Fund Denmark, the Swedish Research Council and the Novo Nordisk Foundation.
