Effects of exercise on bone mass in young women with anorexia nervosa


Journal Title (Medline/Pubmed accepted abbreviation): Med. Sci. Sports Exerc.
Year: 2011
Volume: 43
Number: 5
Page numbers:755-763
doi (if applicable): 10.1249/MSS.0b013e3181ff3961

Summary of background and research design

Background: Patients with anorexia generally have lower bone mineral densities BMD) than their healthy counterparts and some of the bone mass lost is never recovered. However, athletes that engage in high bone loading exercise (such as weight lifting), have a generally higher bone density than average. It is unknown how anorexia and exercise interact in regard to bone density in patients.

Hypothesis: The amount and type of exercise performed both while ill and while recovering will affect the bone mass and BMD of women who had anorexia.

Subjects: Female patients that were admitted to the Toronto General Hospital and/or the Homewood Health Centre for anorexia were eligible for the study; 141 total participated, 85 ill and 56 recovered.  The women were 26 ± 5.1 yrs old, BMI 19.4 ± 3.5.

Experimental design: Cross-sectional
 
Protocol: BMD was measured using dual-energy x-ray absorptiometry (DEXA) at the lumbar spine (LS), femoral neck (FN), and total body (TB).  An interview was conducted to determine the history of their anorexia [specifically type (restricting or binge-purging), length, and severity] as well as other practices and biological phenomena (ex. menstrual history, body weight by year, use of birth control, etc.)  The interview, in conjunction with a physical activity questionnaire, was used to determine frequency and intensity of physical activity from age 10 to present.  Activities were deemed low, medium, or high intensity and participants were divided into 4 exercise groups: 1) MOD-ONLY, 2) HI-ONLY, 3) BOTH, and 4) NEITHER.  The course of their illness was divided into “before ill”, “while ill”, and “while recovered”.  Patients were considered “recovered” if they had maintained a BMI of ≥ 18.5 kg/m2 and spontaneous menstruation for at least 1 yr.
 
Summary of research findings
  • Participants generally increased their exercise load and/or intensity during their ill phase.
  • About 60% of the participants were engaged in high intensity exercise before anorexia, and the most common type of exercise was competitive sports such as gymnastics, competitive dance, and figure skating.
  • Those engaged in moderate loading exercise showed a lower BMD at the TB, but there was no difference in the LS or FN.  There was a positive correlation between high loading exercise and BMD at the FN but not the LS or TB.
  • When controlling for the duration and severity of illness, those involved in moderate exercise during the illness had a lower BMD than those involved in high or low intensity exercise.
  • When participants engaged in high loading exercise while recovered, there was a positive association with BMD.

Interpretation of findings/Key practice applications

As in healthy women, those who have had anorexia display a positive correlation between high intensity exercise and BMD and the effect was greater in participants who had recovered from anorexia.  However, there was a negative association between moderate exercise while ill and BMD.  With that said, moderate intensity exercise during illness and BMD were not negatively correlated in those who had recovered from anorexia (these results came from a different cross-section of people).  It is possible that the bone loss observed from moderate exercise can be recovered when the patient recovers from anorexia.  The course of anorexia is different for every individual and there are many factors that contribute to BMD, rendering the analysis very complex; the type or exercise performed as well as the time in the course of the illness may have large effects on long-term BMD.


Limitations

One comparison the study makes is between patients with anorexia and patients that have recovered from anorexia. More conclusions could have been made if it were the same patients that were followed through the course of the disease and recovery periods.

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