The Bare Bones of Bone Health in Eating Disorders

Written by Annabella Hochschild and Haley Davis in consultation with Laurel Mayer, MD.

Though eating disorders are, by definition, disorders of the mind, they can be incredibly hard on the body. The physiological toll varies by individual and condition but in general includes heart health, reproductive functioning, and changes to hormones.

Bone health is another domain sometimes impacted by the presence of an eating disorder. To understand the potential effects of an eating disorder on bones, there are first some basics on bones to review:

What do our bones do?

Bones give our body structure. When attached to our muscles, they keep us standing and moving. Bones keep fit by constant remodeling: Osteoclasts chew up bone (a process called bone resorption), and osteoblasts build it back up (bone formation). Bones are also the storehouse of some key minerals (e.g. calcium and phosphorous).

When do our bones stop growing?

Many people believe that when their body is done growing so are their bones. Not true! While we all familiar with the growth spurts of puberty, bone mass continues to accrue until our late twenties.

How is bone health evaluated?

Bone health is measured by determining how many grams of minerals are contained within a particular bone region, also known as ‘bone density’. Fewer minerals per area result in lower bone density, which generally means bones are weaker and may be more prone to fracture. The most common way to evaluate bone density is with a dual-energy X-ray absorptiometry (DXA) scan. Results are often reported in T- or Z-scores, which allow providers to easily compare them to what would be expected for a healthy person of similar age and sex. MRI, quantitative CT (QCT), peripheral QCT (pQCT) and ultrasound scans can also be used to evaluate bone health.

Certain markers in blood and urine can also be measured to monitor bone health. Some markers are related to bone formation, while others are related to bone resorption. As previously mentioned, these processes should be in a state of equilibrium. However, if your bone resorption levels are much higher than your bone formation levels, this could indicate that your bones are at greater risk.

Bone Health in Anorexia Nervosa

Poor bone health is a well-known physical consequence of anorexia nervosa.

Why does bone health commonly suffer in people with anorexia nervosa?

People with anorexia nervosa severely restrict their food intake, which means the body is not getting enough of the nutrients it needs. If you aren’t getting enough calcium or phosphate (and to a lesser extent, potassium, iron, sodium, chlorine, sulfur, magnesium and fluoride) in your diet—your body makes up the difference by triggering a hormone called parathyroid hormone which when released prompts the osteoclasts (those pesky cells that break down bones) to go into your bones and get more calcium. This means that in the case of acute anorexia nervosa, the body continually “borrows” minerals from the bones but has trouble replenishing them.

What kinds of problems come along with having unhealthy bones?

Osteopenia and osteoporosis are common conditions in AN. Osteopenia, a condition of reduced bone mass, occurs when the body does not make bone as fast as it is resorbing bone. It is less severe than osteoporosis. Osteoporosis, which literally means “porous bone,” occurs when the body loses too much bone, makes too little bone, or both. It is a characterized by brittle bones that are prone to weakness and breakage. Sometimes these conditions are not diagnosed until fractures have already occurred; in fact, osteoporosis is so rare in pre-menopausal women that we don’t even know how rare it is.

How can bone health be improved in anorexia nervosa?

For bone health to improve, weight restoration is essential. Improved nutrition and weight gain helps the osteoblasts significantly increase bone mass even before the resumption of menses inhibits osteoclasts and bone resorption.

Oral hormone replacement has not been shown to improve bone density in women with AN. However, an intriguing treatment study to improve bone health in teens with AN looked at whether an estrogen patch which releases estradiol (a hormonal precursor) through the skin and into the body, thus bypassing the not-so-well-functioning gastrointestinal system, might be helpful. Estrogen decreases bone resorption and is a mainstay of treatment in post-menopausal osteoporosis. This study included 110 girls with AN and 40 healthy controls. The girls were randomly assigned to receive a transdermal patch with either the hormone or placebo. The changes in bone mass were significantly greater at all time points in girls who received the active intervention. More research is needed to validate this as a feasible treatment option.

Does poor bone health last forever?

Even though many medical complications of anorexia nervosa can be reversed (i.e., normalized) with the restoration of weight and normalization of eating and related behaviors, the same may not be true of bone health. As previously noted, bone mass accrues until your late twenties. So, if you recover from AN as a teen or young adult, your bones may fully recover as well. However, if you continue to struggle with AN into your late twenties, thirties, forties or beyond, while improving your eating and weight will have a positive effect on your bones, they may not return to their peak/max bone density.

What can be done if bone health remains poor after weight restoration?

Healthy eating, maintenance of normal weight and spontaneous resumption of menses (natural resumption as opposed to taking hormones orally) is the best initial treatment for osteopenia/osteoporosis. If significant bone density issues continue, it is important to be followed by a bone density expert, usually an endocrinologist. There are various medications options that might be recommended, although, for the most part, the goal may be holding steady and preventing further bone loss.

Bone Health in Bulimia Nervosa

In contrast to anorexia nervosa, less is published about bone health and bulimia nervosa. By definition, people with bulimia nervosa are not underweight. However, certain symptoms that often come along with bulimia nervosa (e.g., restrictive eating outside of binges, purging behaviors) can lead to nutrient deficiencies, hormonal disruptions, and dehydration which may ultimately put bones at risk.

What does the research say about bulimia nervosa and bone health?

There is still a lot to be learned about whether bulimia nervosa leads to poor bone health.  One study found that patients with bulimia nervosa have significant bone deficits, but only if they’ve had anorexia nervosa in the past. Others have reported that these deficits are present in patients with bulimia nervosa, regardless of whether there was a past episode of anorexia nervosa. And yet other scientists report  no differences in bone health between patients with bulimia nervosa and their healthy counterparts.

How do we explain these inconsistencies?

We’re still not sure. These mixed findings have led researchers to wonder what makes certain patients with bulimia nervosa more susceptible to bone loss than others. In fact, some members of our team recently joined in on this conversation. We wondered whether a history of significant weight loss (though not necessarily to the point of being underweight) might lead some patients with bulimia nervosa to have lower bone density than those with bulimia nervosa who had not lost a significant amount of weight. In our group of 73 female outpatients with bulimia nervosa, history of weight loss was not significantly associated with bone mineral density, although a past diagnosis of anorexia nervosa was related to poorer bone health [Farahmand P, Tabares P, Davis H, Lowe M, Cohen A, Mayer L. Impact of Weight Suppression on Bone Health in Bulimia Nervosa. (Poster presentation for Academy for Eating Disorders 2018 International Conference)].

What is the takeaway message?

While the link between bulimia nervosa and bone health is still unclear, this is a topic that should not be ignored. Poor bone health is one of the longest-lasting effects of eating disorders, commonly extending even after recovery. Research is ongoing to help us understand more about the effect of bulimia nervosa on bones. In the meantime, patients are encouraged to speak with their treatment providers about any concerns related to bone health to determine if further evaluation is warranted.

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