COMMENTARY

Old Bones: Anorexia Nervosa Can Give a Teen the Skeleton of a 70-Year-Old

Madhusmita Misra, MD

Disclosures

August 05, 2022

Madhusmita Misra, MD

The 19-year-old 5 ft 5 in young woman who came to see me in my clinic was a long-distance runner who had sustained several stress fractures of her feet and legs over the past few years. She admitted to restricting her caloric intake because she "ran better at a lower weight" and because she "looked good when she weighed less than 105 pounds." She had not had her period for over a year (amenorrhea).

This young woman was eventually diagnosed with anorexia nervosa, a condition associated with impaired body image, restricted food intake leading to low body weight, and an intense fear of weight gain. A loss of periods is common but is not required for diagnosis.

A dual-energy x-ray absorptiometry (DEXA) scan revealed very low bone density at multiple sites. Like 22-year-old singer Jackie Evancho, my patient's bones resembled those of a much older woman; in fact, I would put her bone density in the same range as someone in their 70s.

My patient was also diagnosed with the female athlete triad — a condition of low energy availability, where energy intake is insufficient to meet the needs of energy expenditure from excessive exercise, associated with irregular or absent menses and low bone density.

Teens With Anorexia Nervosa Face Serious Loss of Bone Mass

Low bone density, which increases fracture risk, is a serious consequence of anorexia nervosa, seen in both women and men. Men account for 5%-15% of individuals with this eating disorder.

Low bone density has been reported as early as 6-12 months after a diagnosis of anorexia nervosa. A longer duration of illness and of loss of periods is associated with lower bone density.

Teens with anorexia nervosa present a particular concern because this is the age at which bone mass typically increases markedly. This increase in bone mass is essential for optimizing one's peak bone mass or one's "bone bank," achieved in the early to mid-20s.

Anorexia nervosa in teenagers results in very little or no increase in bone mass over time, with serious consequences for peak bone mass acquisition. The lower one's peak bone mass, the greater the risk for impaired bone health and fracture risk in later life. There is also an immediate increase in fracture risk from low bone density.

Factors that contribute to low bone density include body composition and hormonal changes. A decrease in muscle mass occurs with weight loss, which has a harmful effect on bone at almost every site.

Many hormonal changes occur due to the energy-deficit state, which in turn has negative effects on bone. These include low levels of estrogen (important for preventing bone loss and possibly increasing bone formation), insulin-like growth factor-1 (IGF-1) and leptin (the latter two are both important for bone formation), and relatively high levels of cortisol (which has multiple deleterious effects on bone) and peptide YY (which reduces bone formation).

Improve Bone Density by Reaching a Healthy Weight

The best strategy to improve bone density is to get to a healthy body weight. The goal is a body weight above that at which menses were lost. If periods never stopped, the person's doctor can provide guidelines regarding goal weight based on the patient's height and population norms. Calcium and vitamin D intake should be optimized.

A multidisciplinary treatment team is strongly recommended to assist with recovery, with the primary care provider or an eating disorder specialist coordinating care. A dietitian is necessary to provide directions regarding caloric intake; exercise activity should be curtailed until the individual reaches a healthy weight.

People with anorexia nervosa should be under the care of a psychologist or psychiatrist to assist with recovery and prevent relapses, which unfortunately are common. Anorexia nervosa is also associated with high rates of anxiety, depression, and suicide, and a psychiatrist or psychologist can work with the patient and help manage these concerns. For athletes, the coach or athletic trainer should be engaged in the treatment team whenever possible. For children and adolescents, parental involvement is essential.

Bone density assessment should be repeated every 1-2 years to determine trends over time. If a woman with anorexia nervosa does not regain her periods after 6-12 months of robust lifestyle intervention, estrogen replacement should be considered.

How Else Can Bone Density Be Improved?

Giving estrogen as an oral contraceptive pill is not effective in increasing bone density in anorexia nervosa because oral estrogen reduces levels of IGF-1 (necessary for bone formation) and also causes other biochemical changes that account for its lack of efficacy. Instead, the physiologic (natural) form of estrogen — delivered via a patch applied to one's skin — is effective because it does not suppress IGF-1 and has other beneficial effects on bone. If estrogen is administered continuously as the transdermal patch, a progesterone pill should be given cyclically for at least 12 days of every month to prevent a buildup of the uterine lining over time (from the use of estrogen only), as this increases the risk for uterine cancer.

Women who continue to fracture despite all of these measures may require additional interventions to improve their bone density. This requires the involvement of a bone health expert.

With the help of an eating disorder specialist, a dietitian, and a psychologist, my patient had an improvement over time in her weight, and her menses resumed with an improvement in bone density. However, she did lose her periods again after a year from relapse of her eating disorder when she stopped seeing her treatment team. Eventually, the treatment team was reinstated and I also started her on transdermal estrogen with cyclic progesterone. She has since had steady improvement in her eating behaviors and bone density.

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