Orthopedic Complications of Anorexia Nervosa

The Effects of Anorexia Nervosa on Bone Health

Anorexia nervosa (AN) can increase the risk for bone health issues, including osteopenia, osteoporosis, fractures and more. The longer an individual lives with AN, the more dramatically their bone health will be affected.

The age of onset of the eating disorder also plays a role. Those who develop AN at younger ages may experience more severe bone health issues than those who develop AN when they are older. This is because early adolescence is a key time for bone growth and development, with peak bone mass normally achieved during adolescence.

Since the peak age of onset of AN is during adolescence and since the bone loss associated with AN can be irreversible, many people who have suffered with AN — of all ages — are at risk for long-term bone health complications.

Anorexia Nervosa, Hormones and Bone Health

Food restriction, bingeing, and purging are all hallmarks of AN. Over time, these behaviors can impact bone health through various factors: BMI and lean muscle mass, hormonal changes, exercise and medications.

• BMI and lean muscle mass: Both BMI and lean (muscle) mass are important determinants of bone mineral density. A low BMI, as seen with malnutrition, and changes in body composition including a decreased lean mass that develop with restriction of Calories, both negatively impact bone density. Bone growth occurs when muscle exerts forces on bone, and with reduced muscle mass, or sarcopenia, this effect on bone is lost.

• Exercise: Exercise has a deleterious effect on bone density when malnourished or amenorrheic (not having periods), although it is beneficial to bone health when at a healthy weight (and when done in a healthy manner). 
• Hormonal changes: There are multiple hormonal changes that develop with malnutrition that also negatively impact bone health but we will focus on a few below:
  • Gonadal hormones, including estrogen and testosterone, are deficient in malnutrition, and both are critical for bone growth in adolescence and bone density maintenance in adults.
  • Growth hormone is one of our major anabolic, or growth, hormones produced by the pituitary gland within the brain. It has numerous functions including building up of bone but is unable to do its job appropriately when an individual is malnourished.
  • Cortisol, our major stress hormone, is up-regulated with malnutrition to help combat some of the physiologic and metabolic changes that accompany malnutrition. However, this hormone also acts to break down bone, thus impacting bone mineral density.
  • Adipokines and gut hormones: Adipokines, hormones secreted from our fat cells, and gut hormones, secreted from our gastrointestinal tract, have numerous metabolic effects in the body but also impact bone density. The changes to these hormone levels with malnutrition ultimately have a deleterious effect on bone density.
• Medications: Some medications used to treat the comorbid medical and psychiatric conditions seen with eating disorders can negatively impact bone disease and/or vitamin D metabolism, which is very important for bone density. (These medications are often necessary but it can still be worth having a conversation with your treatment team regarding the pros and cons of using certain medications.)

Anorexia Nervosa and “Brittle Bones”

It is very common for individuals with AN to have reduced bone mineral density. Bone density is a measurement of the strength of one’s bones. Reduced bone mineral density is more common in those who developed AN during their youth because bone accrual is an ongoing process that tends to peak during adolescence, with a gradual reduction in bone density occurring thereafter, even in those not suffering from malnutrition. However, this reduction in bone density is accelerated in those with malnutrition, due to the reasons stated above.   

Because patients who develop AN at younger ages may never reach peak bone mass, they are at risk for several concerning problems throughout their lifespan:

• Fractures (broken bones) — AN can triple an individual’s risk for bone fractures
• Chronic pain associated with bone fractures
• Reduced strength and mobility
• Emotional suffering associated with a chronic illness, such as osteoporosis, and/or associated with pain
• Shorter stature
• And more

In summary, the loss of bone mineral density is highly prevalent in individuals with AN and in many cases, this loss of bone mineral density is irreversible and associated with potential long-term complications.  

Frequency of Low Bone Mineral Density with Anorexia Nervosa

In a study of 281 adult patients with extreme AN with a mean body mass index (BMI) of 12.1 kg/m² (range = 7.5–15.7) at admission, low bone mineral density was diagnosed in almost 90% of the patients, with 45% of individuals presenting with osteopenia and 43% with osteoporosis. 

• Osteopenia: a mild loss of bone mineral density.
• Osteoporosis: severe loss of bone mineral density. Unfortunately, osteoporosis in patients with AN can persist despite weight gain and the return of regular menstrual cycles.

Treating Osteopenia & Osteoporosis & Treatment Outcomes

When patients are able to gain weight with AN, this has a strong impact on bone mineral density, particularly when hormonal health is also restored. Indeed, one study found an increase in bone mineral density of up to about 3% following weight gain and menstrual recovery. While this may not sound like much, this is similar to the benefits found with some pharmacologic therapies that could be recommended depending on the severity of loss of bone mineral density. Targeted medications coupled with vitamin supplementation and lifestyle interventions may decrease one’s bone fracture risk, enhance overall bone density and contribute to an improved quality of life. In certain cases, specialized medical stabilization may be necessary for severely compromised patients with AN who are at very low body weights (BMI<15).

If you are unsure about your own bone health, and you have a history of AN, consider asking your doctor about a DEXA (dual energy x-ray absorptiometry) scan, which is the most frequently used test to diagnose low bone mineral density. This painless test can evaluate the extent of bone loss, and findings from the scan may even motivate you to focus on a full and lasting eating disorder recovery.

Bone density loss is one of the more common complications associated with AN. While few medical providers are trained to identify and safely treat this issue and other medical concerns stemming from AN, providers need to be cognizant of this serious complication because bone density loss tends to become more pronounced as the severity of the eating disorder increases.

References

• Anand, P., & Mehler, P. S. (2019). Osteoporosis recovery in severe anorexia nervosa: a case report. Journal of Eating Disorders, 7(1). https://doi.org/10.1186/s40337-019-0269-8
• Gibson, D., Watters, A., Cost, J., Mascolo, M., & Mehler, P. S. (2020). Extreme anorexia nervosa: medical findings, outcomes, and inferences from a retrospective cohort. Journal of Eating Disorders, 8(1).
• Steinman, J., & Shibli-Rahhal, A. (2019). Anorexia Nervosa and Osteoporosis: Pathophysiology and Treatment. Journal of Bone Metabolism, 26(3), 133.
• Workman, C., Blalock, D. V., & Mehler, P. S. (2020). Bone density status in a large population of patients with anorexia nervosa. Bone, 131, 115161.

Last Reviewed: December 2023 by Dennis Gibson, MD, FACP, CEDS