I was excited to see that my recent survey about sleep/wake habits here on the blog supported my hypothesis: that those with restrictive patterns tend to rise earlier, and those with more binge/purge patterns rise later. Of course, in order to really look at the data, I'd need to compare the early bird and night owl percentages of each category with those of a non-ED sample.
Although many things affect circadian rhythm--most of which are under genetic control--one of the key hormones is cortisol. Released from the adrenal cortex, cortisol levels generally peak upon waking and reach a low point shortly after you go to sleep. What's more, cortisol is released during times of stress or anxiety, increasing both blood pressure and blood sugar.
A PubMed search of eating disorders and circadian rhythm produced mainly results on night eating syndrome. However, one study found a negative correlation between awakening cortisol response and "high anxiety, disinhibition and hunger scores, as well as poor body esteem and a high weight preoccupation" in women, but not men. That means that women with a low awakening cortisol response have high levels of anxiety, poor body esteem, etc. Of course, we don't know if this is cause or effect- just that it exists.
A study in men found a significant relationship between cortisol and perfectionism, which makes sense. Perfectionism is stressful (and don't I know that!), and higher stress means higher cortisol. As well, abnormalities in cortisol have been found in other psychiatric disorders, such as depression.
And indeed, women with anorexia were found not only to have higher cortisol levels but a significant proportion lacked a circadian cortisol rhythm. These abnormal cortisol levels are directly related to the starvation state- after weight restoration, cortisol levels return to normal. I'm not sure how the lack of cortisol rhythm is important. In general, starvation disturbs the sleep cycle, and refeeding is typically associated with improvements in sleep. The general school of thought is that the body is urging the starving person to go get food, and this may be true. But the high levels of cortisol brought out by the stress of malnutrition and starvation may also play a role.
High cortisol levels in people with AN have been positively associated with both osteoporosis and
Although one study found that overall daily cortisol rhythms in normal weight bulimic women were pretty much the same as in healthy women, another found evidence of greatly increased cortisol levels. It appears that, in bulimia, cortisol levels might be much higher than usual, although they still have a daily rhythm, unlike in anorexia. Even recovered bulimic patients continued to show a hyperreactivity to corticotropin-releasing hormone, which stimulates the release of cortisol, indicating an underlying neuroendocrine dysfunction.
Yet when cortisol levels were examined in relation to impulsivity, researchers found an inverse relationship between cortisol levels and impulsivity:
Patients with bulimic symptoms had significantly higher rates of cortisol suppression than controls and than restrictive anorectic patients. Percent cortisol suppression showed a strong and significant correlation with the patient's score on the Barratt Impulsiveness Scale. A hypersensitive cortisol response to dexamethasone, which might reflect hypothalamic-pituitary-adrenal axis dysfunctions might be specifically associated with impulsive subtypes of eating disorders.
Clearly, cortisol is just one player on a much larger field. Nor is it clear whether abnormalities in cortisol levels are cause or effect, and perhaps it's a little bit of either. Certainly the eating disorder exaggerates any underlying abnormalities. Whether the ED behaviors themselves cause the specific differences observed in cortisol levels in anorexia and bulimia, or whether these differences are part of the underlying risk factors for these illnesses also remains unclear.