Bone health and eating disorders

A recent study from the Journal of Bone and Mineral Research found that women with anorexia had much higher levels of fat in their bone marrow than women without AN (Ecklund et al, 2010). The study was generally publicized as "OMG! Anorexics have FAT on their bony bodies!" Which, as an interesting irony and news hook, I'll give you. But the story goes much deeper than that, which some of the news coverage touched on but really didn't delve into (they appeared to get stuck on the "WTF- could anorexics be fat?!?" part).

Eating disorders are associated with an increased risk for osteoporosis--and it ain't no joke. I've learned that the hard way, with three broken bones and several stress fractures. There are many hypotheses for this increased risk, including deficits in estrogen, high levels of cortisol, and high levels of leptin. I'm guessing each of these plays a role in the decrease in bone mass and density through either the metabolism of bone cells and/or a dramatic decrease in the formation of new bone cells during malnutrition.

This study points to a new mechanism for the dramatic bone density decrease seen in eating disorders in general and anorexia in particular. At the center of larger bones is the bone marrow, one type of which is the red bone marrow and produces new blood cells. The other type is the yellow bone marrow and contains fat cells that can be used as an energy source in cases of extreme starvation. Furthermore, the two types of bone marrow can be interchangeable--in cases of extreme blood loss, the yellow marrow can be converted to red marrow. What Ecklund et al found in this most recent study is that red marrow can be converted to yellow marrow if the body is profoundly starved, which can result in premature osteoporosis.

The study subjects with anorexia had much higher levels of yellow marrow than red marrow, and the researchers hypothesized that the body had prioritized the formation of extra fat for future energy needs at the expense of red blood cell formation (I'm wondering whether this also helps to explain the high levels of anemia seen in people with eating disorders). The innate intelligence of the body never ceases to astound me. In a starving person, fat (which is essentially energy) is much more useful than red blood cells. Without energy, the body shuts off. With fewer red blood cells, you may be more easily fatigued, but mild levels of anemia are rarely out-and-out life threatening.

It will be interesting to see if there is follow-up research done to see how weight restoration and recovery change the ratio of red and yellow marrow, and whether these changes persist for a long period of time after recovery.

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16 comments:

Tiptoe said...

Although the headline is purely for enticement, I thought that study was really interesting. It's just another way the body adapts and tries to keep the starved person alive even if it is in a future sense.

I do wonder about the whole anemia bit. In the worst of my ED days, my serum and transferritin iron levels were incredibly low. Would it have been the fat in my marrow that kept me going?

I agree, further research in recovered individuals would be good to see whether this changes or stays stagnant.

Cathy (UK) said...

Interestingly, Kreipe et al. observed fatty infiltration of bone marrow in patients with low weight anorexia nervosa (AN) in 1993. (I carry this info around in my head; it was linked to my PhD research).

Although low levels of oestrogens (and especially the most biologically active forms) as well as high levels of cortisol and low (not high) levels of leptin - and also low IGF-1 contribute to disturbed bone metabolism in AN, a major problem is reduced numbers of osteoblasts (i.e. the bone cells that form new bone).

Blood cells and bone cells are produced from the same precursor cell line - and so starvation is accompanied not only by reduced bone formation (and bone loss), but also reduced numbers of red and white blood cells. A deficit of red blood cells reduces oxygen transport and contributes to anaemia, while a deficit of white blood cells leads to immunesuppression.

Thus, osteoporosis, anaemia and immunosuppression are interrelated in starvation/AN.

Fiona Place said...

There are probably a whole range of after-effects from having been through a period of starvation. Bone health is important and no doubt just like every other woman a woman who at one time had an eating disorder may well need to consider a calcium supplement. However while many of these medical results are intriguing what is more important is that every woman lives well. And not too preoccupied with such after-effects.

Katie said...

Oh, how interesting. When I was really ill my white cell count was through the floor (my doctor's phrase was 'like someone going through cancer treatment', ack), and I always wondered how eating disorders led to suppressed immune systems. I love the media's take on it, oh dear! I really hope someone does a similar study in recovered individuals as well. My neutrophil count is back in the normal range now, so I guess that bodes well :)

Cathy (UK) said...

To Fiona Place:

Hi Fiona, I agree with the gist of your post, but it is important that women who have osteoporosis as a consequence of having previously had anorexia nervosa (AN) are VERY aware of their bone health.

Bone is lost very rapidly in AN, and children who develop AN pre-puberty or during puberty may fail to ever build up an adequate bone mass (unless they are able to gain weight and keep it on) because they miss out on a crucial stage of physical development.

People with long histories of AN (like me), in whom the ED started pre-teens, cannot hope to ever have normal bone mass. For that reason they need to be vigilant and careful what activities they engage in. Even a minor bump or trip can result in devastating fractures.

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Cammy said...

I am continually amazed as more and more research comes out on how dynamic and "active" our bones are in relation to our overall health. I think often people think of skeletons as a barren, static framework for everything else, so it's fascinating to learn about how in-tune they are to various aspects of body condition.

kallista93 said...

This is a timely post for me, beccause my daughter & I have been reading about the skeletal system, because she checked out some library books about it (she's 7). It's also scary, because I am recovering from AN & haven't had a period in years (not since I stopped nursing above mentioned 7 year old) & am wondering just how irreperable the damage I have done is. So I want to find out what happens to the bones of the recovered for my own & for curiosities sake!
The body is so fascinating, & the things it does to survive while being starved is pretty amazing. I like to think, just as we've learned the brain is more plastic than we previously thought, that the bones may have an ability to re-build, too. I haven't taken a bone density test - too scared! - but I am being very careful, & trying to make sure I do all your supposed to do to protect/strengthen my bones. And also warn my own daughter against starting that first diet.
Sorry for the de-rail! Thanks for the info, & all the info on this site.

Sarah said...

I found this very interesting. I had hydrostatic weighing done in a Bod Pod late July 2008 (bad idea) and found that I had a fairly high body fat percentage (30%.) The technician actually re-did the test because he was shocked that my body fat was that high when my physical appearance did not reflect it at all. I was working with a trainer to prepare for my wedding and was pretty muscular, healthy BMI, on the pill, and abdominal fat or the pill were his best explanations because even he didn't believe the test. I sort of just brushed it off and agreed to keep working out the same amount, etc. because I was already healthy so what more could I really do? Screw the test. But I've always been curious what happened.

Since I have no background in this area I don't know how it all works, but does it seem remotely plausible that maybe the test was picking up some fat in my bones? What do you think, Carrie or Cathy?

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I'm a science writer, a jewelry design artist, a bookworm, a complete geek, and mom to a wonderful kitty. I am also recovering from a decade-plus battle with anorexia nervosa. I believe that complete recovery is possible, and that the first step along that path is full nutrition.

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