Anorexia nervosa is an eating disorder with one of the highest mortality rates of all psychiatric disorders. It is estimated that as many as 4% of women in the west will have the condition at some point in their life.
The illness, which usually starts in adolescence, is difficult to treat. Only around half of those treated recover, so preventing it is really important. However, to effectively prevent a disorder, you need to be able to identify the early signs.
Restrictive eating, restricting the number of calories or quantity of food consumed, is not only a core feature of anorexia but it is also an early symptom that precedes anorexia onset. In our latest study we wanted to understand whether anxiety disorders predicted restrictive eating.
We were interested in a particularly severe form of restrictive eating, which was fasting for an entire day for weight control (losing weight or avoiding weight gain). We assessed whether having an anxiety disorder predicted how likely people were to fast in the future, two years after the anxiety assessment.
Previously, researchers found that people with anorexia had higher rates of anxiety disorders compared with the general population. This led some scientists to suggest that restrictive eating may reduce anxiety in people who are at risk of developing anorexia. The reduction in anxiety resulting from restrictive eating may then encourage restrictive eating to continue.
Our research included 2,406 girls from the Avon Longitudinal Study of Parents and Children, a project studying the health and wellbeing of babies born in the early 1990s in Bristol. The participants’ anxiety disorders and fasting behaviour were measured three times between the ages of 13 and 18. Using this data, we were able to investigate the links between anxiety disorders and fasting across adolescence.
We found that girls who had anxiety disorders when they were aged 13 or 15 were twice as likely to report fasting two years later, compared with those without an anxiety disorder. We also found that girls who reported fasting were at increased risk of developing anorexia nervosa. Collectively, the findings point toward the possibility that having an anxiety disorder reflects a vulnerability for developing anorexia.
Early warning, early intervention
Outcomes of our study suggest who might be most at risk of an eating disorder, so it could be useful in highlighting people who might benefit from eating-disorder prevention efforts.
Our findings mirror observations in anorexia nervosa patients that worsening eating-disorder symptoms accompany increases in anxiety. It is important to recognise, however, that our findings don’t tell us about how anxiety disorder and eating-disorder symptoms are associated. In particular, outcomes do not necessarily reflect that anxiety disorders cause fasting.
Clarifying whether the association we observed is causal is important. Should this be the case, it may be that targeting anxiety disorder symptoms is an effective way of reducing the chance of an eating disorder developing.
An alternative explanation for the patterns we see in our data is that anxiety disorders and restrictive eating are caused by the same things. This would also lead to the two occurring together in people.
Recent findings from a large scale study of the genetics of anorexia nervosa supported there being common genetic risk factors for anorexia and anxiety disorders. We consider this possibility in our ongoing work, which is focused on better understanding exactly how anxiety disorder and eating-disorder symptoms are associated.
Our study only included girls, so our conclusions may not apply to teenage boys. Future research should consider the presence of associations between anxiety disorder and disordered eating symptoms in boys and men. This will promote a fuller understanding of relationships between psychiatric symptoms and disorders across different groups in the population.