Serotonin, impulsivity, and eating disorders
Serotonin is the brain chemical we've all come to know and love. It's sometimes called the "happy chemical." Why? People with depression tend to have low levels of serotonin in the brain. So do people with anxiety disorders. And bulimia nervosa.
Anorexia appears to be a little different. While researchers know that people with anorexia have abnormal serotonin levels both during illness and after recovery, the levels in recovered anorexics tend to be higher than usual. A review article from 1997, followed by a study from 1998, says that
Certain traits, such as negative affect, behavioral inhibition, compliance, high harm avoidance, and an obsessive concern with symmetry, exactness, and perfectionism, persist after recovery from anorexia nervosa. These persistent symptoms raise the possibility that such traits exist premorbidly and contribute to the pathogenesis of this disorder. Such traits could be associated with increased brain serotonin activity.
But an interesting study came out recently that linked low serotonin levels to impulsivity and aggression.
A press release said that the study results
"highlight why some of us may become combative or aggressive when we haven't eaten. The essential amino acid necessary for the body to create serotonin can only be obtained through diet. Therefore, our serotonin levels naturally decline when we don't eat, an effect the researchers took advantage of in their experimental technique.
The research also provides insight into clinical disorders characterised by low serotonin levels, such as depression and obsessive compulsive disorder (OCD), and may help explain some of the social difficulties associated with these disorders."
Restrictive eating causes a drop in serotonin, temporarily normalizing mood. Then, of course, the not eating continues and serotonin continues to drop. This drop in serotonin also helps to (temporarily) decrease anxiety.
The chaotic eating surrounding bulimia may also help explain the dramatic rise in impulsivity seen in people with this illness. Besides possibly having a lower-than-average level of serotonin, the periods of food restriction that often accompany bingeing and purging could further lower serotonin levels, making the impulses to binge and purge even harder to resist. Purging also lowers serotonin, compounding the situation even further.
It also, I might add, explain why dieters are so darn cranky!
If anyone can help explain why people with anorexia have higher rates of pre-illness OCD and high serotonin levels (when OCD is associated with low serotonin), I would greatly appreciate it.
5 comments:
I think the answer to your last question is...nobody really knows how this stuff works. If they did, they'd stop freaking contradicting themselves and pretending they're not.
Such as: if anxiety & OCD are common precursors to anorexia, then why are the first two associated w/ low serotonin, and the latter with high? (Wait, that was your question!) It also doesn't quite make sense that "obsessive concern with symmetry, exactness, and perfectionism" is a high serotonin trait, while OCD is associated with low serotonin. Or that "negative affect" is a high serotonin trait...but depression comes from low serotonin?
And the impulsivity/aggression issue...that one doesn't make a whole lot of sense to me either. I wouldn't think of OCD as being associated w/ impulsive behavior--quite the opposite. And how many aggressive, impulsive depressives are out there? Are they internally aggressive and impulsive but just too depressed and exhausted to act on it? :-P I sure as hell wasn't either of those things when depressed--I was way more likely to sit inside terrified of the world ("high harm avoidance?")and belabor decisions to death b/c I was sure I'd screw something up ("perfectionism?"). Except...wait, those are high serotonin traits! And what about panic disorder (anxiety, ergo low serotonin) with agoraphobia (harm avoidance, ergo high serotonin)? I could go on and on...
I do think the why-dieters-are-cranky hypothesis makes a lot of sense though!
Sorry for the rant--I get pissy b/c research on EDs and depression tends to completely diverge from my own experience, leading far too many shrinks to put me in a box based on a DSM prototype and then refuse to believe me when I jumped up and down and hollered (okay, protested once or twice and then silently seethed, got frustrated as hell and cried in my car) that they were talking to me about a "me" I didn't recognize. Then they fed me Freudian bullshit about denial, told me I was engaging in "black & white thinking" and made me do worksheets. (Yeah, I'm bitter. Inexperienced IOP program shrinks suck hard core.)
Okay, now I'm reallly done ranting. Sorry!!! (An interesting post though...I think I'm off to do a little nerdy research on the topic...hehehe)
I think neurobiology will explain a lot as to why people behave that they do. Its definitely a burgeoning field that we should watch. But Im a biologist.
I think all the researchers are able to do is show that there's some link between serotonin levels (low, high, normal, whatever) and specific problems/behaviours. They just don't have enough information to say that one thing causes the other or if there's some common cause or if they're both related to something hitherto unthought of. All the researchers are able to say is, "We pretty certain that x is somehow related to y."
The problem is when journalists, politicians or people trying to sell diet aids look at the research as misquote the scientists: "x causes y."
Maybe disregulation of the system (either on the high or low side) looks similar, although the levels of very different, while well-regulated average levels look/feel healthy?
Yeah, I'm kind of wondering if some people have a sort of paradoxical response to serotonin, and that's why you see things like OCD and such and low serotonin levels. Or that it's something to do with an ability to process these neurochemicals.
Or maybe, like you said Anon, it's the dysregulation that causes symptoms rather than the specific levels.
This is why, if I had to go to med school, I would likely do neuropsych. Or infectious disease, but that's another story.
Thanks for your thoughtful input.
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