Biological Explanations for Anorexia Nervosa

Clinical characteristics of anorexia

- anxiety

- excessive fear of becoming fat

- persistent restriction of energy intake

- significantly low body weight (BMI)

- avoid food and meals

- weighing and portioning food

- body image distortion

- amenorrhoea

- pale, hair loss, and lanugo (hair growing all over body)

Genetic explanation

= our genes are inherited

... consist of DNA strands

- Our DNA gives us physical features and specific physiological features (neurotransmitter levels and size of brain structure)

- These may impact on psychological features such as intelligence and mental disorders

Genetic explanation - Scott-Van Zealand et al. (2014) (candidate genes)

... looked at 152 candidate genes

- Discovered 1 gene was significantly associated with AN

=> it's an enzyme involved in cholesterol and metabolism

·

-When people are in acute stage and the characteristics start to develop, AN individuals have an abnormally high level of cholesterol

Genetic explanation - genome wide association studies

Looking at the entire collection of human genes - polygenic

Genetic explanation - Borasks et al. (2014) (genome studies)

... 5,551 AN patients and 21,080 matched controls

- 72 separate genetic variations were identified but none were significantly related to AN

- Researchers argued their study was not sensitive enough to detect any genetic influence

Genetic explanation - Holland et al. (1988) (twin studies)

compared concordance rates in MZ and DZ twins to find support for genetic cause

MZ = monozygotic

DZ = dizygotic

Procedure:

- 25 MZ and 20 DZ female twins (45 pairs in total)

- Interviewed twins where at least one twin had anorexia

- Questions were asked about body mass, length of amenorrhea, drive to be thin, body dissatisfaction and incidence in relatives

Holland et al. (1988) Twin study FINDINGS

- 14 (56%) of MZ twins concordant for anorexia - both twins had anorexia

- 1 (5%) of DZ twins were concordant for anorexia

=> Greater similarity for MZ twins in body mass, amenorrhea, drive to be thin and body dissatisfaction

Holland et al. (1988) twin study CONCLUSIONS

this shows that anorexia has a large genetic component: heritability may be as large as 0.80

- Also, factors such as body mass and drive to be thin could be genetic because it is closer in MZ twins than DZ twins

- What is inherited is a genetic sensitivity to environmental factors (pre-disposition)

Heritability

Heritability is a measure of how well differences in people's genes account for differences in their traits

=> heritability estimates range from 0-1

Holland et al. (1988) twin study STUDY REPLICATION

the study was replicated several years later with less dramatic findings

- An MZ concordance rate of 65%

- A DZ concordance rate of 32%

... still strong evidence for the role of genes

Holland et al. (1988) twin study CRITICISMS OF STUDY

- Diagnosis of anorexia is not always correct so it may be a predisposition to development of mental disorder/eating disorder but not anorexia specifically

- MZ twins may be treated more similarly than DZ twins and therefore greater concordance due to the environment

Genetic explanation - Spring Babies Vulnerability

a season-of birth effect in anorexia nervosa

Disanto et al. 2011

Disanto et al. (2011) Spring Babies vulnerability

Disanto et al. (2011)

=> conducted a meta-analysis

- Pooled a total of 1,294 anorexia nervosa births which were compared with those of the general population

- Found an excess of anorexia births from March to June

- The excess of spring births could be the consequence of environmental factors acting at any time from conception to the first post-natal months

- Seasonal changes in temperature, sunlight exposure, and consequent vitamin D levels, maternal nutrition and infections are all strong candidate factors

...demonstrates a susceptibility to AN is significantly influenced by the season of birth, with higher rates in those individuals born in the spring and lower ones in those born in the autumn

Neural explanations

high serotonin level

low serotonin levels

dopamine

the brain

Neural explanations - high serotonin levels

... People with eating disorders often have high levels of anxiety too, which may be due to high levels of serotonin

- As serotonin is made from tryptophan (an amino acid which comes from food), reducing food intake reduces tryptophan, causing serotonin levels and anxiety to drop

=> this makes sense as many anorexics say they feel less anxious when they don't eat

- Insufficient dietary intake of tryptophan can lead to low serotonin levels (plentiful in oats, bananas, fish, poultry, sesame seeds and chickpeas)

... reduced eating to reduce anxiety from naturally high serotonin levels

Tryptophan

an amino acid that comes from food and forms serotonin

Neural explanations - low

... Research has shown that people who are currently suffering from anorexia have significantly lower levels of serotonin than individuals without an eating disorder

=> this likely a sign of starvation, since the body synthesises serotonin from the food we eat

Low levels of serotonin - Attia et al. (2014)

... studied AN patients who had not returned to their pre-disorder weight

- These individuals responded less well to drugs that stimulate serotonin activity than AN patients who had restored a healthy weight

- The pattern of results clearly indicates underactivity of the serotonin system

homovanillic acid (HVA)

Major metabolite of dopamine

Neural explanations - dopamine

... new research suggests that women who develop anorexia nervosa may have altered levels of dopamine in their brains

- Findings have been inconsistent, but it has been suggested that there is a decreased level of dopamine in AN patients

- Dopamine disturbances can cause hyperactivity, repetition of behaviour (such as food restriction) and anhedonia (a decreased sense of pleasure)

- Research has focused on homovanillic acid (HVA) a metabolite of dopamine which is decreased in AN patients

Dopamine - Kaye et al. (1999)

...HVA levels are lower in recovered AN patients compared with control participants

Dopamine - Bailer et al. (2012)

... administered amphetamine to their participants to increase the release of dopamine. Healthy participants experienced euphoria but AN patients experiences anxiety

=> as eating increases dopamine release, it may be that AN patients restrict their food intake as a means of reducing their anxiety levels

Neural explanations - the brain (Lipsman et al. 2015)

... found that dysfunction in parts of the limbic system in the brain can lead to deficits in emotional processing, which may cause some of the pathological thoughts and behaviour shown by a person with AN

AO3 WEAKNESS - genetics + twin studies

P

A limitation of the biological explanation is the validity of twin studies.

EX

To compare concordance rates we have to assume that MZ and DZ twins are treated equally, and we cannot conclude that differences in AN concordance rate are due to genetic factors if they are not.

EV

Joseph (2002) argues that MZ twins are treated more similarly than DZs in many aspects by their parents, friends, teachers, and other acquaintances. This greater environmental similarity means that heritability estimates are artificially inflated.

EXT

In addition to this, much research with candidate genes has been inconclusive and the actual heritability of the disorder is still unknown. Pineiro et al (2010) suggested that no one gene can be responsible for the wide variety of physical and psychological symptoms that characterise AN, so the search for a single gene is "futile".

LB

This suggests that anorexia is polygenic, and many other factors such as the environment play a larger role than originally thought.

AO3 WEAKNESS - biologically reductionist

P

Furthermore, the biological explanation has been criticised for being biologically reductionist as it does not provide a full explanation of anorexia nervosa.

EX

The biological explanation for AN cannot account for why the disorder primarily affects females and why it is more prevalent nowadays. The inheritance of genes from generation to generation hasn't greatly changed, yet the number of sufferers has increased.

EV

Women have anorexia rates three times higher than males, with 0.9% of the population affected compared to 0.3% for men, and according to the Royal College of Psychiatrists, hospital admissions for eating disorders have increased by 84% in the last 5 years.

EXT

As well as this, the biological explanation does not acknowledge how psychological, social, or cultural factors may contribute to the development of AN. Strober et al. (2006) found high levels of perfectionism in 75% of girls receiving treatment for AN and 50% of boys. This demonstrates how personality traits affect AN and the complexity of eating disorders.

LB

Therefore, the biological approach can be criticised for reducing complex behaviours to simplistic ideas, such as genetics, reducing its validity.

AO3 STRENGTH - research support

P

There is supporting evidence for the link between dopamine and AN.

EV

Kaye et al. (1999) found that the levels of the dopamine metabolite homovanillic acid (HVA) were lower in recovered AN participants compared with control participants.

EX

This is significant as most studies look at HVA levels in people currently experiencing the symptoms of AN, therefore their malnutrition may account for the lower HVA levels. In Kaye's study, however, because these low HVA levels persist after recovery, it suggests that the disturbance of dopamine may be a causal factor for AN.

EXT

There is also research that proposes that serotonin and dopamine are secondary to the activity in noradrenaline in AN and that AN can be better explained by considering the interaction between serotonin and noradrenaline. Nunn et al. (2012) reported that abnormal noradrenaline functioning leads to high anxiety and insula dysfunction which results in negative body image distortion.

LB

This is a strength of neural explanation as provides evidence that supports the role of neurotransmitters in relation to Anorexia Nervosa.