Bone Health and Anorexia Nervosa in Women, Men, and Adolescents
This month, the International Journal of Eating Disorders published a vital new study on the heightened risk of bone fractures in adolescent girls with anorexia nervosa. (See the Academy of Eating Disorder’s press release here: http://www.aedweb.org/web/index.php/2-uncategorised/141-press-release-increased-fracture-risk-for-girls-with-anorexia-nervosa) The authors identify for the first time that girls and young women with anorexia nervosa (AN) have a 60% increase in fractures compared with age-matched controls, even when bone scans did not necessarily show a reduced bone mineral density. The higher risk for fracture was observed as early as one year into the diagnosis of AN, and the results were independent of the amount of exercise being done. This is the first time a study has looked at fracture risk in girls and adolescents with anorexia nervosa, and it’s a big deal. In this post, I’m going to tell you why.
You may be someone with an eating disorder, a parent/partner/sibling/teacher/coach/grandparent of someone who has an eating disorder, or a clinician. You are all welcome to read on…everyone who has anything to do with eating disorders should understand why bone density loss and underweight are linked. I want you to understand the basic science behind the linkage, to grasp what’s at stake, and to use this scary example of objective body suffering to break through the syndrome of “I’m fine.”
So let’s start with some basics. During adolescence, 90% of your bone density is laid down…that’s the healthy, strong, resilient bone that has to carry you around the rest of your life, so it’s incredibly important. After age 20, the window to lay down this dense bone closes, and you will live in a balance of building up and breaking down bone until (if you’re a woman) menopause, at which point you’ll probably slowly start losing more bone density than you make because you no longer produce estrogen. There are a number of ways to measure bone density, but the most widely known and used one is called a DEXA (bone densitometry) scan, and young people’s scores are reported as a “Z-score.” Generally speaking, if your Z-score is higher than -1 (it’s an awkward scale system), you have pretty normal bone density. If it’s between -1 and -2.5 (or in some cases -2.0), you’re diagnosed with osteopenia, which means moderate bone density loss. If it’s lower than -2.5 (or -2.0), you’re diagnosed with osteoporosis, or severe bone density loss.
Why do we care about bone density at all, much less in the context of eating disorders? Well, when you have low bone density, you have a higher risk of fractures. That could mean a stress fracture that occurs during normal athletics which can sideline you, or it can mean a fracture when you should have just gotten a bruise, like in a fall during skiing, or it can mean the bones of your spine slowly squish down even without a fall, just from walking around, and you end up shorter in height than you should have, with a permanent hunchback, chronic pain, or even the need for surgery and internal metal bracing. Not good.
Here’s how anorexia nervosa (or other causes of underweight, like the Female Athlete Triad, which is: too little food for how much you’re exercising, menstrual irregularity, and bone density loss) ties in with bone density loss. When you’re underweight, your very clever “cave girl brain” (the one that stuck around below your level of consciousness and still rules a lot of what happens in your body) gets the message that you’re not in a safe nutritional space to get pregnant. As a result, your hypothalamus gets turned back in time to pre-adolescence, which means you stop producing estrogen and other hormones, and you stop ovulating and getting your period regularly. Low estrogen levels cause bone density to turn over faster…essentially to break down. At the same time, your body is being stressed by starvation and weight loss. That physiologic stress raises your stress hormone cortisol, which reduces bone formation. Other hormones like IGF-1 and testosterone drop, which also contributes to arrested bone formation.
The result? Bone density drops fast and early in AN. Many patients spend those critical adolescent bone formation years in various degrees of starvation, underweight, relapse, brief recovery, and more relapse. That means they never lay down that vital adolescent bone density at all. 50% of adolescents may have osteopenia, while a full 25% may have actual osteoporosis. 90% of adult women may have osteopenia, and 40% or more may have full osteoporosis. And osteoporosis is the one medical complication of AN which may never fully resolve, even when the person has been in full recovery (oh happy outcome) from AN for years.
What’s amazing to me is how many of my patients—and I see some of the most medically complicated adult patients in the country—have never had their bone density checked. Especially the men I care for…they’re an even more underserved population, maybe because they don’t have that trigger for further evaluation that women do, the loss of the menstrual period. Men with AN actually get osteoporosis faster and more severely than women, at higher BMI levels…and they may fracture at “better” bone density than women. If you’ve been underweight 6-12 months (and as a post-adolescent woman, have gone 6 months without your period), you should ask your doctor for a DEXA scan.
I find that an abnormal DEXA result can have a profound impact on my patients with AN, who fight on a minute-to-minute basis with the eating disorder voice telling them they aren’t sick enough for treatment, don’t deserve to get better, and feel ambivalent about recovery. When one of my patients learns she’s got osteopenia or osteoporosis, it’s an irrefutable sign of body suffering. She’s not “doing fine” with her starvation and insistence on underweight (even if she is making a 4.0 or is the star employee at work)…to the contrary, she learns her bone density may be irreversibly damaged by her AN. This can be a big motivator for recovery, or at least give the “healthy voice” something to say back to the eating disorder voice when it’s being loud and painful.
(Stay tuned for Part 2: Treatment of bone density loss in anorexia nervosa, and consideration of athletes and bone density…)
- Faje AT, Fazeli PK, Miller KK, Katzman DK, Ebrahimi S, Lee H, Mendes N, Snelgrove D, Meenaghan E, Misra M, Klibanski A. Fracture risk and areal bone mineral density in adolescent females with anorexia nervosa. Int J Eat Disord 2014;47(5): 458-66.
- Mehler, Philip S. and Andersen, Arnold E. Eating Disorders: A Guide to Medical Care and Complications. Baltimore: Johns Hopkins University Press, 2010. Print.
- Olmos JM et al. Time course of bone loss in patients with anorexia nervosa. Int J Eat Disord 2010;43(6):537-42
- Mehler PS, Sabel AL, Watson T, Andersen AE. High risk of osteoporosis in male patients with eating disorders. Int J Eat Disord 2008;41(7):666-72