While bulimics may have low levels of serotonin, other studies indicate that anorexics have high levels of neurotransmitters in some areas of the brain. For example, researchers in London found that anorexics have an overproduction of serotonin, which can cause a continual state of acute stress and anxiety. Reducing their intake of calories to starvation level, which in turn leads to decreased levels of serotonin in the brain, may result in a sense of calmness. The exact relationship between serotonin and anorexia has yet to be clarified, however. Researchers are still puzzled as to why, if anorexics already have high levels of serotonin, then SSRIs (medications like Prozac which raise serotonin levels) are successful treatments for some individuals. These scientists speculate that that there may be different subtypes of this disease, and that different groups of anorexics may have different neurochemical characteristics.
Researchers have also noted that abnormal eating behaviors and the resulting changes in the body can actually cause a disruption in serotonin levels, thus contributing to an already existing problem. Abnormalities in serotonin levels can lead to depression and anxiety, both for under-eaters and over-eaters, as well as other mental disorders such as Obsessive Compulsive Disorder, Bipolar Disorder, Borderline Personality Disorder, and Attention Deficit/Hyperactivity Disorder (ADHD). Studies also suggest that there are genetic predispositions to serotonin disruptions that appear to run in some families.
New research suggests that women who develop anorexia nervosa may have altered levels of dopamine in their brains. Dopamine disturbances can cause hyperactivity, repetition of behavior (such as food restriction), and anhedonia (a decreased sense of pleasure). This neurotransmitter also affects reward-motivated behavior. Improper levels of dopamine may explain why anorexics feel intensely driven to lose weight yet feel little pleasure in shedding pounds.
Numerous other hormones in the brain have also been linked to eating disorders. Stress triggers the production and release of a hormone called cortisol; chronically elevated cortisol levels have been observed in patients with both anorexia and bulimia. Cortisol is very important in preparing multiple body systems to deal with threat (including the heart, lungs, circulation, metabolism, immune systems, and skin). Cortisol also inhibits the release of a powerful appetite stimulant (in other words, increased cortisol results in decreased appetite). This process may serve as a link between stressful conditions and the later development of eating disorders, although some imaging studies indicate that stress-hormone related changes occur after the disorders have developed. It is currently unclear whether changes in stress hormones are a cause or a result of eating disorders.
Leptin is a protein hormone produced by the body's adipose (fat) tissue. This hormone travels to the brain, where it tells the body how much energy is available. This information plays a part in the regulation of reproduction, appetite, metabolism, and bone formation. If individuals with eating disorders lose extreme amounts of body fat, leptin levels drop (a condition called "hypoleptinaemia"). The side effects of hypoleptinaemia can include amenorrhea (when a female's period stops), impaired metabolism, and bone loss.
Interestingly, leptin levels do not immediately return to normal when someone receives treatment for an eating disorder. Initially during therapy, leptin levels often increase dramatically as people gain weight. Researchers think that during this period of increased leptin production, individuals with eating disorders are at great risk for relapsing into disordered eating behavior and failing to maintain weight gains. For most people, it takes approximately 6 months or more of sustained, effective treatment before leptin levels return to normal. It is crucial, then, that people who are receiving therapy for eating disorders stick with a treatment program for the long haul (at least six months) to ensure that their bodies are returning to normal hormone levels. As with stress hormones, it is not entirely clear whether changes in leptin levels are a cause or a result of eating disorders.