What You Should Know About Anorexia Nervosa and Bone Health

Recovery from an eating disorder is really hard. Unfortunately, the negative effects of that occur as a result of the eating disorder often persist long after recovery. It is hard to undo the mental and psychological aspects of anorexia or bulimia nervosa, but it may be just as hard, if not impossible, to undo the damage done to body.

What are some of the long-term health effects of eating disorders? What do patients with eating disorders – recovered or not – have to live with, for years, often decades, after recovery?

A really common consequence of anorexia nervosa is osteoporosis: thinning of bone tissue and loss of bone density. Unlike delayed gastric emptying – another consequence of EDs – which can make every meal a nightmare (particularly for someone recovering from an eating disorder): acid reflux, stomach pain and abdominal bloating are just some of the symptoms, bone density loss is easy to overlook. You don’t feel its effects (not initially, anyway), you probably wouldn’t even know it is happening. Many are unaware of just how quickly bone health can deteriorate and how difficult it may be to repair the damage. 

Probably more than half of young women  with anorexia nervosa develop osteoporosis,  and relatively quickly. Baker et al obtained bone scans in a series of 56 young women, mean age 27 years, who had had an eating disorder for  a mean of about 10 years, and found that the bone mineral density in the femur was below the critical fracture threshold in 42 (75%).

A review paper by Dr. Kathryn Teng, published last year in the Cleveland Clinic Journal of Medicine, provides a concise overview of the prevalence, risk factors and treatment of osteoporosis in patients with anorexia nervosa.

The mean age of onset for anorexia nervosa is in the early to mid teens, a time which coincides with puberty, rapid growth and bone development. Although bone density continues to increase into the 20’s, the majority occurs during adolescence. According to Teng, 40-60% of bone mass in women, is gained between the ages of 11 and 14.

This overlap is important because it can have huge implications later in life:

 …small differences in bone density can have significant clinical implications later in life: a 5% increase in bone density significantly decreases fracture risk, whereas a 10% decrease in adult  bone mineral density is associated with a two to three times higher risk of fracture…

What causes bone density loss in anorexia nervosa? The main factors are low body weight (a risk factor that is independent of anorexia nervosa – that is, naturally thin people are also at a higher risk of osteoporosis) and amenorrhea (the absence of menses). In anorexia, the absence of menses results from hypothalamic dysfunction. The hypothalamus regulates appetite, thirst, mood, libido and body temperature, among other things. In AN, chronic restriction suppresses the release of a hormone called the gonadotropin-release hormone, which leads to a decrease in FSH (follice-stimulating hormone) and LH (luteinizing hormone), leading to a “prepubertal low-estrogen state.” This results in hypothalamic (also known as secondary) amonrrhea. Moreover, the duration of amenorrhea appears to be correlated with the extent of bone density loss.

The list below is modified from Table 1 in the Teng (2011) paper.

POTENTIAL FACTORS INFLUENCING BONE DENSITY IN ANOREXIA NERVOSA

Undernutrition

• low body weight appears to contribute to bone density loss independently of menses (that is, undernutrition in the presence of menses is still detrimental to bone health and conversely, weight restoration even without return of menses is beneficial)

Deficiency in insulin-like growth factor 1 (IGF-1)

• IGF-1 regulates proteins involved in bone formation and AN is associated with low levels of IGF-1, resulting in reduction of bone-forming proteins
• (click here for a short, point-form summary of endocrine effects on bone)

Low androgen levels

• androgen appears to play a role in maintaining bone health in males, however the role in female is less clear, moreover, oral contraceptives reduce androgen levels but whether this is harmful, according to Teng, is not yet known.
• (click here for a nice detailed summary of androgens & bone health)

Hypercortisolemia

• elevated levels of the stress hormone cortisol have been noted in patients with AN
• levels of cortisol are inversely correlated with levels of a bone-forming protein and this may lead to loss of bone density

Increased osteoprotegerin

• helps preserve bone density
• appears to be higher in females with AN than controls, may be released in an attempt to preserve bone density

There may be potential roles for leptin (leptin role in bone health), ghrelin and obestatin in regulating bone density, but further studies are necessary. 

Teng also summarizes common treatments for bone density loss and the evidence supporting each treatment in anorexia nervosa patients.

PREVENTION & TREATMENT OPTIONS FOR OSTEOPOROSIS IN ANOREXIA NERVOSA

When it comes to prevention and treatment of low bone density, weight restoration is by far the most effective and evidence-based approach. Weight gain normalizes hormone levels which play important roles in regulating bone health.

Although vitamin D supplements haven’t been shown (consistently) to improve or prevent bone density loss in AN patients, given that most individuals do not get enough vitamin D, supplementation, as Teng writes, “is almost universally recommended.” (Vitamin D and bone health)

What about hormone (estrogen) therapy?

This is where premenopausal and postmenopausal women differ. In postmenopausal women, hormone replacement therapy is effective in improving bone density (here is a nice summary of the benefits and risks of HRT in preventing osteoporosis in postmenopausal women). The reason that HRT does not seem to be of much benefit to premenopausal women is likely due to the fact that the mechanisms underlying bone loss are different – the physiology is just not the same.

Despite the documented association between anorexia nervosa and estrogen deficiency and the strong correlation between osteoporosis and the duration of amenorrhea, most studies have found no improvement in bone mass with hormonal therapy. In particular, three randomized, placebo-controlled trials have been published to date, and not one showed a significant improvement in bone mineral density with estrogen therapy compared with placebo in patients with anorexia nervosa… [Moreover] restoring regular menstrual cycles with oral contraceptive pills will not normalize the metabolic factors that impair bone formation, health, and performance and is not likely to fully reverse low bone mineral density…

Weight-bearing exercise is often suggested to postmenopausal women to prevent bone density loss. However, the effects weight-bearing exercise appears to benefit only the weight-bearing sites, and its effect in patients with AN is not fully determined. Moreover, due to the high prevalence of compulsive exercise in AN, caution should be exercised (hehe).

More studies are needed to identify the role of IGF-1, leptin and ghrelin as potential stimulators of bone growth and bone density.

Although bisphosphonates have been shown to significantly increase bone mineral density in young women with AN, there are significant side-effects that must be considered: bisphosphonates are tetragenic (that is, they can cause birth defects) and have a long half-life, meaning that they may be present even 2 years post discontinuation.

Hilariously (in my opinion), the idea of using cannabinoids to promote weight gain (munchies!) and thus improving bone health, was once a promising area of research. But alas, this didn’t pan out: one trails suggested that patients who ingested THC (the psychoactive ingredient in cannabis) had an increase in sleep disturbances (what??) and interpersonal sensitivity, but no effect weight gain. Similarly, another study showed no changes in weight but an improvement in depression and perfectionism scores.

So for now weight restoration and nutritional stabilization remain the key treatments in preventing bone density loss and reducing the risk of osteoporosis.

SOME IMPORTANT THINGS TO KEEP IN MIND

This review paper has some interesting points that I wasn’t completely aware of until now. Particularly that the standard dual-energy x-ray absorptiometry (DEXA) test “may not be able to distinguish bone that is small but o fnormal density from bone that is of low density.” This may potentially be a significant problem, particularly for short females such as myself. Moreover, as Teng points out, another pitfall of testing for bone density in premenopausal women is that it is possible they have not yet reached their peak bone mass.

Furthermore, Teng writes:

… density by itself is not a perfect tool for predicting who will or will not experience a fracture, particularly in premenopausal women. Most premenopausal women with low bone mineral density but no other risk factors for fracture such as previous fractures or glucocorticoid therapy are at very low short-term risk of fracture.

Regardless, or rather, despite these limitations, DEXA tests are still important tools to identify osteoporosis. More importantly, though, is tracking the changes in bone density over time – as these changes might provide a better understanding of the initial peak bone mass, the rate of increase or decrease in bone density and so on.

Despite its limitations, until newer risk assessment tools are available for this patient population, measuring bone mineral density is still recommended in addition to assessing clinical risk factors to diagnose osteoporosis. Also, changes in bone mineral density over time can help to assess risk and guide treatment.

References

Teng, K. (2011). Premenopausal osteoporosis, an overlooked consequence of anorexia nervosa. Cleveland Clinic Journal of Medicine, 78 (1), 50-8 PMID: 21199907