Why do some people get anorexia and not others?

It is clear that there is no single cause for anorexia and that it stems from a mixture of social, psychological and biological factors.

Current research is commonly focused on explaining existing factors and uncovering new causes. However, there is considerable debate over how much each of the known causes contributes to the development of anorexia. In particular, the contribution of perceived media pressure on women to be thin has been especially contentious.

The Body

Genetic factors
Family and twin studies have suggested that genetic factors contribute to about 50% of the variance for the development of an eating disorder and that anorexia shares a genetic risk with clinical depression. This evidence suggests that genes influencing both eating regulation, and personality and emotion, may be important contributing factors.

Neurobiological factors
There are strong correlations (but nothing proven) between the neurotransmitter serotonin and various psychological symptoms such as mood, sleep, vomiting, sexuality and appetite. A recent review of the scientific literature has suggested that anorexia is linked to a disturbed serotonin system, particularly to high levels at areas in the brain which are particularly linked to anxiety, mood and impulse control.

Recent studies also suggest anorexia may be linked to an autoimmune response to melanocortin peptides which influence appetite and stress responses.

Nutritional factors
Zinc deficiency causes a decrease in appetite -- which could degenerate in anorexia nervosa.

Psychological factors
There has been a significant amount of work into psychological factors that suggests how biases in thinking and perception help maintain or contribute to the risk of developing anorexia.
Anorexic eating behavior is thought to originate from feelings of fatness and unattractiveness and is maintained by various cognitive biases that alter how the affected individual evaluates and thinks about their body, food and eating.

One of the most well-known findings is that people with anorexia tend to over-estimate the size or fatness of their own bodies. A recent review of research in this area suggests that this is not a perceptual problem, but one of how the perceptual information is evaluated by the affected person. Recent research suggests people with anorexia nervosa may lack a type of overconfidence bias in which the majority of people feel themselves more attractive than others would rate them. In contrast, people with anorexia nervosa seem to more accurately judge their own attractiveness compared to unaffected people, meaning that they potentially lack this self-esteem boosting bias.

People with anorexia have been found to have certain personality traits that are thought to predispose them to develop eating disorders. High levels of obsessionality (being subject to intrusive thoughts about food and weight-related issues), restraint (being able to fight temptation), and clinical levels of perfectionism (the pathological pursuit of personal high-standards and the need for control) have been cited as commonly reported factors in research studies.

It is often the case that other psychological difficulties and mental illnesses exist alongside anorexia nervosa in the sufferer. Clinical depression, obsessive compulsive disorder, substance abuse and one or more personality disorders are the most likely conditions to coexist with anorexia, and high-levels of anxiety and depression are likely to be present regardless of whether they fulfill diagnostic criteria for a specific syndrome.

Society

Sociocultural studies have highlighted the role of cultural factors, such as the promotion of thinness as the ideal female form in Western industrialised nations, particularly through the media. A recent epidemiological study of 989,871 Swedish residents indicated that gender, ethnicity and socio-economic status were large influences on the chance of developing anorexia, with those with non-European parents among the least likely to be diagnosed with the condition, and those in wealthy, white families being most at risk.

A classic study demonstrated that those in professions where there is a particular social pressure to be thin (such as models and dancers) were much more likely to develop anorexia during the course of their career.

Western Culture and Anorexia

Although anorexia nervosa is usually associated with Western cultures, exposure to Western media is thought to have led to an increase in cases in non-Western countries. However, it is notable that other cultures may not display the same 'fat phobic' worries about becoming fat as those with the condition in the West, and instead may present with low appetite with the other common features.

There is a high rate of child sexual abuse experiences in those who have been diagnosed with anorexia (up to 50% in those admitted to inpatient wards, with a lesser prevalence among people treated in the community). Although prior sexual abuse is not thought to be a specific risk factor for anorexia (although it is a risk factor of mental illness in general), those who have experienced such abuse are more likely to have more serious and chronic symptoms.

Anorexia and the Internet

The Internet has enabled anorexics and bulimics to contact and communicate with each other outside of a treatment environment, with much lower risks of rejection by mainstream society. A variety of websites exist, some run by sufferers, some by former sufferers, and some by professionals.