What are the causes of anorexia nervosa?

Causes of Anorexia Nervosa

Anorexia nervosa is a multifactorial disorder caused by the interaction of genetic neurobiological vulnerabilities (particularly serotonin and noradrenergic dysregulation), premorbid psychological traits (perfectionism, negative self-evaluation, anxiety), and environmental stressors (family dynamics, sociocultural pressures, trauma). 1, 2

Neurobiological Factors

The strongest evidence points to inherent brain chemistry abnormalities as foundational causes:

• Serotonin (5-HT) dysregulation: Brain imaging studies demonstrate persistent alterations in serotonin function both during illness and after recovery, suggesting this is a trait-related vulnerability rather than a consequence of starvation. This dysregulation contributes to the characteristic anxiety, obsessionality, and mood disturbances seen in AN 2

• Noradrenergic dysfunction: Genetically determined noradrenergic dysregulation leads to high baseline anxiety, impaired neuroplasticity, and regional cerebral hypoperfusion. This particularly affects the insula, explaining the pathognomonic body image distortion that defines the disorder 3

• Reward pathway alterations: Inherent dysregulation of emotional and reward pathways affects the hedonic aspects of feeding, making these individuals vulnerable to disturbed eating behaviors 2

Psychological Predisposing Traits

These traits consistently precede illness onset and persist after recovery, confirming their role as vulnerability factors rather than consequences:

• Perfectionism and high self-demands: The most commonly reported premorbid characteristic, significantly more prevalent than in general psychiatric controls 4, 5
• Negative self-evaluation: Particularly characteristic antecedent distinguishing eating disorders from other psychiatric conditions 5
• Obsessive-compulsive traits: High constraint, constriction of affect, anhedonia, and asceticism 2
• Anxiety disorders: Often present in childhood before eating disorder onset 2

Family and Environmental Factors

Critical distinction: The 2020 Gut guideline 1 emphasizes that family factors include both genetic transmission and psychosocial influences:

• Parental psychiatric disorder: Particularly maternal psychopathology including somatization and anxiety 6
• Negative family communication patterns: Over 80% of individuals with weight concerns report parental/sibling negative comments about weight, shape, or eating, strongly associated with emotional abuse and lower self-esteem 6
• Early life trauma and ongoing life stresses: Interact with genetic vulnerabilities 1
• Lack of social support: Compounds other risk factors 1

Sociocultural Pressures

While sociocultural factors alone cannot fully explain AN 3, they act as triggers on vulnerable individuals:

• Societal emphasis on thinness: Particularly impacts adolescents during puberty 2
• Weight-related teasing and bullying: 52-60% of overweight youth report weight-based teasing, with 70% subsequently engaging in restrictive eating 6
• Dieting behaviors: Adolescents who diet are 18 times more likely to develop an eating disorder than non-dieters; even moderate dieting increases risk fivefold 7

Developmental Triggers

Puberty acts as a critical vulnerability period through multiple mechanisms:

• Hormonal changes: Female gonadal steroids exacerbate underlying serotonin dysregulation 2
• Age-related neurobiological changes: Amplify pre-existing vulnerabilities 2
• Peak onset timing: Early to mid-adolescence for AN, with notable increase in 15-19 year old girls 7

The Vicious Cycle Mechanism

Understanding causation requires recognizing the self-perpetuating nature:

1. Initial restriction: Individuals discover that reducing dietary intake temporarily reduces dysphoric mood by modulating brain serotonin activity through decreased tryptophan availability 2

2. Reinforcement: This brief respite from anxiety powerfully reinforces restrictive behaviors 2

3. Malnutrition effects: Weight loss and caloric restriction alter neuropeptides and monoamine function, paradoxically exaggerating the dysphoric mood they were meant to relieve 2

4. Chronicity: This creates a self-maintaining cycle explaining why AN becomes chronic despite devastating consequences 2

Common Clinical Pitfall

Do not attribute AN solely to "wanting to be thin" or cultural pressures. The 2012 research 3 explicitly states that sociocultural pressures alone cannot fully explain the wide range of AN features. The disorder requires pre-existing neurobiological vulnerability that interacts with environmental triggers. Recognizing this prevents oversimplified explanations that miss the underlying pathophysiology and may delay appropriate multidisciplinary treatment including psychiatric and medical management 1, 8.

Risk Factor Hierarchy

Based on the 1999 case-control study 5, the most distinguishing risk factors for AN specifically (versus bulimia nervosa or general psychiatric disorders) are:

1. Premorbid perfectionism (most characteristic)
2. Negative self-evaluation (most characteristic)
3. Anxiety and obsessional traits
4. Family psychiatric history

Notably, factors that increase likelihood of dieting have less influence on AN risk compared to bulimia nervosa 5, suggesting different etiological pathways despite superficial similarities.