(4) Biological Explanations for Anorexia Nervosa

Family Studies: Research shown that AN runs in families. 1st degree relatives have a x10 greater risk of it. Also an increased risk of developing other eating disorders in relatives of those diagnosed with AN. Suggests that people may inherit a general vunerability to eating disorders rather than just AN. 

Twin Studies: Generally sugges moderate/high inheritability of AN - between 28% to 74%. Also an interview of over 2,000 female MZ and DZ evaluating them using the DSM criteria for AN. Results: Heritability rate 58% - suggest some people are more genetically predisposed to develop AN.

Adoption Studies: Problem in twin studies = share genes and environment. Adoptions share genes but not environment. 123 adopted sibling pair studied and 56 biological sibling pairs. Low prevalence of AN so disordered eating symptoms tested instead - heritability rate 59% to 82% with non-shared environmental factors.

Serotonin: Disturbances in levels of serotonin seem to be a characteristic of people with eating disorders. Bailer et al measured serotonin activity in women recovering from restricting-type anorexia or binge-eating/purging and compared them to healthy eating controls. Results: Higher serotonin activity in the women recovering from binge-eating compared to the other 2 groups. Also found highest levels of serotonin = women with most anxiety suggesting persistent distruption of serotonin levels = increased anxiety = trigger AN.

Dopamine: PET scan to compare dopamine activity in 10 women recoving from AN and 12 healthy women. Results: Overactivity in dopamine recetors in the basal ganglia in the AN women. Increase dopamine in this area alters the way people interpret rewards. AN find it difficult to associate good feeling with things people find pleasurable.

Limbic System Dysfunction: Research suggests that the neural roots of AN seem to be related to a dysfuction in the limbic system. Claim that dysfunction in these areas can lead to deficits in emotional processing - may lead tp the thoughts/behaviours that are typical of AN

Problems with genetic explanations: Fairburn et al concluded that the actual heretability of AN is still unknown because studies have been inconsistent with their estimates - wide ranges. Also violate the 'equal environments assumption'. Twin researchers assume MZ/DZ raised in the same homes experience similar environments. But research suggests MZ twins tend to be treated more similary - suggests the claim that the greater concordance for AN in MZ compared to DZ twins must be due to greeater genetic similarity.

Genetic explanations ignore the role of the media in AN: Assumes environmental factors such as media aren't relavant. Media's idealisation of thin bodies has been viewed as important risk factor for ED's. Bulik suggests genetically vunerable individuals might seek out images of thin role models in the mdeia to reinforce their body image - supported by a longitudinal study - found that teen girls whos AN increased over 16mths also reported a significantly greater fashion magazine reading over the same period

Real-world application: Is AN really biological in nature: Some argue that AN isn't 'biologiallly based'. It is seen as a psychologial issue in places like the US so doesn't qualify for insurace treatment.

Problems with the serotonin explanation: SSRIs are ineffective when used with AN patients. Ferguson et al found no change in symptoms between AN patients taking SSRI and patients with similar characteristics who weren't taking them. However, Kaye et al found, when used with recovering AN patients the drugs were effective in preventing relapse. Suggests that malnutrition-related changes in serotonin function might negate the action of SSRIs - seem to only become effective when weight returns to a more normal level.

Research support for the dopamine: Research supports the role of dopamine in AN symptoms. Food aversion, weight loss etc. found to be related to increase activity in dopamine pathways. Other evidence = increased eye-blink in AN compared to controls - indicative of higher levels of dopamine activity in the brain. Barbato et al found a signifiant correlation between blink rate and duration of AN - suggests the relationship between dopamine activity and AN symptoms develop overtime.

Advantages of biological explanations of AN: Advantage of reducing the stigma that a patients challenging behaviour with AN is their fault. Also the possiblity of treating AN by regulating the brain areas involved in the behaviours that are characteristic of AN. Lipsman et al used deep brain stimulation to change activity in the subcallosal cingulate in patients with chronic AN - led to improvements in mood.